Biology, care, identification, nomenclature, breeding, and genetics


Ron Banks, USAMRIID Seminar Series 1989





     A.   History and Origin


          1.   Origin of the guinea pig is


           a.   Wild guinea pig is Cavia aperea

           b.   Widely distributed in Argentina,

                 Uraguay, and Brazil

          c.   Cavia cutleri is still wild in Peru


          2.   Spanish found Andean Indians had domesticated Cavia cutleri

               a.   Used as food and for religious sacrifices

               b.   Used for food around Spanish Colonial Empire.


          3.   Paintings such as the last supper have included the guinea pig as

                main course meal.

          4.   Guinea pigs are often apartment reared in Peru today.

          5.   1500's:  Dutch sailors introduced the guinea pig into Europe. 

          6.   1770's:  Probably reached the United States as pets and fancy


          7.   Origin of "guinea pig" name is vague.  Common name used by

               fanciers is "cavy".


               a.   Does resemble a suckling pig

               b.   Is prepared for eating by scalding/scraping

               c.   Some suggest "guinea" was derived from the fact that trading

                     ships may have travelled via Guinea in West Africa,or via Guiana

               d.   Adult females called sows, and adult males called boars. 

                     Parturition referred to as farrowing.

     B.   Taxonomy


     Kingdom - Animal

       Phylum - Chordata (with notochord and gills)

       Subphylum - Craniata (Vertebrata): Chordates with organized head region

               Class - Mammalia (Warm-blooded craniates with hair coat. 

                                               Young nourished from mammary glands)

               Subclass - Theira (Viviparous Mammals = Live Young)

               Infraclass - Eutheria (Placental mammals, versus  Metatherial

                                                  marsupials, and protherial egg layers)

                    Order - Rodentia (single row of upper and lower paired incisors

                                                 which grow continuously; no canine teeth)

                    Suborder - Hystricomorpha ("porcupine like")

                             All except Coypu have (1) a vaginal closure membrane and

                                   (2) a masseter muscle insertion that passes through the

                                   large infraorbital foramen.  Other suborders include

                                   Sciuromorpha:  "squirrel-like" ... such as quirrels,

                                   marmots, gophers, beavers, and Kangaroo rats and the

                                   suborder  Myomorpha: "rat-like"... house mouse,

                                   norway rat, hamsters, voles, gerbils, etc.)

                         Family -  Caviidae (tailless South American rodents with 

                                   (1) one pair of mammae and (2) four digits on front feet

                                        and three digits on hindfeet.

                              Genus - Cavia species - porcellus


     C.   Varieties ("types" or "breeds")

            - Characterized by length, texture, and direction of growth of    hair)


          1.   ENGLISH:

               a.   Short, smooth, straight hair (3.8 cm)

               b.   Solid colors: albino, white, black, agouti, sandy, red,chocolate etc

               c.   Bicolored and tricolored animals also.

               d.   Most inbred and outbred laboratory guinea pigs are the English


          2.   ABYSSINIAN:

               a.   Short, course hair that radiates from multiple  centers on the body

                     to form rosettes.

               b.   Variety of colors.


           3.   PERUVIAN:

               a.   Has long silky hair up to 15 cm (6 in) long.

               b.   Absence of two hip rosettes are referred to by fanciers as

                     "angora" or "shelties".


      D.   Laboratory Stocks and Strains

           1.   Listings of available stocks and strains are provided in the ninth

                edition of the ILAR publication "Animals for Research", and the

                "NIH Rodents 1980 Catalogue"

           2.   Outbred English stocks listed in above sources:

               a.   Dunkin-Hartley--("albino")

               b.   Hartley--("albino")

               c.   Pirbright-Hartley

               d.   Shorthair   

           3.   Inbred Strains: 

               a.   Strain 2 and 13 are the only two inbred

                    guinea pig strains used to any extent.

               b.   Only remaining strains developed by Wright at

                    the U.S. Bureau of Animal Industry in 1915.

           4.   Mutant Stocks/Strains:

               a.   Complement 4 Deficient (C4D/N):

                    (1)  Developed from spontaneous mutation in NIH multipurpose

                          guinea pig stock in 1970.

                    (2)  Partially dominant mode of inheritance; i.e., heterozygotes

                           have intermediate levels of C4 activity.

                    (3)  Most immunologic reactions are normal.

                b.   Waltzer (Wz)

                    (1)  Wz mutation occurred spontaneously in NIH guinea pig stock 

                    (2)  "Waltzing" or circling and deafness develop due to atrophy of

                           organ of Corti cells.

                    (3) Inherited as an autosomal dominant gene with full penetrance.

                    (4)  Homozygous condition results in high perinatal mortality.

                 c.   Hairless and Immunodeficient Mutan:

                    (1)  Spontaneous mutant strain from Hartley stock at Eastman

                           Kodak Company in 1979.

                    (2)  At birth, are smaller, have tannish skin with numerous

                           wrinkles, and have stunted  vibrissae. 

                    (3)  Shortened lifespan; many die during first week, one lived for

                           9 months. Body hairs rare, short, and poorly retained; a few

                           have temporary fuzzy hairs.

                    (4)  No grossly visible thymic tissue, cystic spaces found where

                           thymus should have been. Germinal follicles reduced or

                           absent in lymph nodes and intestinal lymphoid tissues.

                    (5)  Hypogammaglobulinemic.

                    (6)  Deaths due to systemic cytomegalovirus (intranuclear

                           inclusion bodies in cardiac fibers), systemic balantidiasis, and

                           Pneumocystis carinii.

                 d.   Hairless Euthymic Guinea Pigs: 

                    (1)  Now available from Charles River Laboratories.

                    (2)  Hair bulb, erector pili, and sebaceous glands do exist.

                    (3)  Produces defective hair shaft

                    (4)  Reduced number of shafts

                    (5)  Normal functional thymus




     A.   Anatomy

           1.   Skin and external features

                a.   Hair and skin:

                     (1)  Consist of coarse large guard hairs surrounded by undercoat

                            of fine hair.

                     (2)  Each hair follicle has associated sebaceous gland

                     (3)  Sudoriferous glands absent

                     (4)  5-6 rows of tactile hair (vibrissae) on lateral nose

                     (5)  Prominent hairless area (1-1.5 cm diam) just caudal to pinna

                            of each ear.

                     (6)  Perineal Sac:  Bilateral diverticula in circumanal region

                            containing large accumulation of sebaceous glands.  White

                            waxy accumulations termed "scrotal plugs" in males.


               b.   Mammary Glands:

                     (1)  Both males and females have a single pair of inguinal teats

                            surrounded by a hairless area.

                     (2)  A single large papillary duct opens to exterior.

           2.   Dental Formula:

                         1 01 3               

                      2(I-C-PM-M-) = 20 teeth.

                        1 01 3                 


               a.   Diastemal space between incisors and premolars.

               b.   A11 teeth continue to grow for lifetime of the animal.
               c.   The molars are hypsodontic = prism shaped teeth with high


               d.   With medial inclinement of the teeth and continuous growth,

                     encasement of the tongue may occur 

               e.   Only one set of teeth (monophydont)


           3.   Bones


               a.   Vertebral formula:C7,T13-14,L6,S2-3,Co4-6

                          6 sternebrae. 13 or 14 pairs of ribs: 

            1st-6th sternal, 7th-9th contribute to costal arch, 10th-14th are floating

                b.   Feet: 

                         Forefeet have 4 digits each:

                              (3 phalanges in each digit except 4th which has 2)

                         Rear feet have 3 digits each.

                c.   Vestigial clavicles present.

                d.   Pelvic Girdle:

                     (1)  Consist of ilium, ischium, acetabulum, and pelvis bones.

                     (2)  Pubic symphysis generally remains fibrocartilage throughout

                            life of animal.

                     (3)  The pubic symphysis degenerates 2 weeks prior to parturition

                             resulting in complete destruction by parturition

                     (4)  Palpation of separation can be used to estimate parturition.

          4.   Muscular System

                a.   Well developed masticatory muscles (Masseter and digastricus)

                b.   Reflects the gnawing behavior and corresponding mastication by

                      grinding (versus chewing).


          5.   Cardiovascular/Respiratory System

                a.   Pharynx:

                     (1)  Soft palate is continuous with base of the tongue and lateral

                            walls of the oral cavity

                     (2)  Opening into larynx is a small intrapharyngeal ostium

                b.   Lungs: 

                     (1)  3 left lobes (cranial, middle, caudal) and 4 right lobes

                           (cranial, middle,  caudal, accessory)

                     (2)  Pleural cavities are continuous (LAS 16(5): 411, 1966)

                c.   Arteries:  3 deviations from normal mammalian vascular pattern

                      (Amer. J. Anat. 139, 269- 284. 1974):

                     (1)  There may be 2 or 3 pairs of renal arteries (versus normal 1

                            pair in most mammals).

                     (2)  The abdominal aorta gives rise to a celiomesenteric trunk

                            instead of separate celiac  and cranial mesenteric arteries.

                     (3)  A bronchoesophageal artery passes from the right subclavian,

                            the right internal thoracic, or the brachiocephalic trunk

                            instead of from the aorta.


          6.   Hemolymphatic System


                a.   Thymus:  Present in immature animal

                     (1)  Gradually involutes as the animal matures.

                     (2)  In adults may be completely gone or persist in caudal

                            cervical or cranial  mediastinum. 

                     (3)  Thymic tissue is replaced primarily with fat as age


                     (4)  In immature animals it is composed of 2 compressed

                            lobulated glands on each side  of the ventral cervical midline.

                     (5)  Extends from the angle of the mandible approximately

                            halfway to the thoracic inlet (Cooper and Schiller, 1975).

                     (6)  Accessory thymic lobes in most guinea pigs; usually paired

                            and adjacent to the  parathyroid gland

                     (7)  Guinea Pig used extensively for immunologic studies because

                            the cervical  thymus is easily removed


               b.   Parathymic Lymph Nodes: 

                     (1)  Located in cervical region.

                     (2)  Receive lymph from the thymus. 

                     (3)  Studied to determine the immunologic inter-relationship

                            between the thymus and lymph nodes.


          7.   Gastrointestinal System

                a.   Tongue: 

                     (1)  Rostral one-third is free.

                     (2)  Remainder attached to floor of oral cavity. 

                     (3)  Small filiform papillae 

                b.   Stomach: 

                     (1)  No keratinized non-glandular portion present

                c.   Small Intestine:  

                     (1)  About 125 cm (50 in) in length

                     (2)  Common bile duct enters duodenum 1 cm caudal to pylorus.

                d.   Cecum:

                     (1)  Occupies left side of abdominal cavity

                     (2)  Large thin-walled sac 15-20 cm long.

                     (3)  Accounts for about 15% of body weight.

                     (4)  Has 3 taenia coli (dorsal, ventral and medial) 

                     (5)  Produces out-pouchings called haustra.

                e.   Peyers patches: 

                     (1)  About nine flat white 1 mm diameter area of lymphocyte

                            aggregates on mucosal surface.

                f.   Colon: 

                     (1)  Ascending, spiral ascending, transverse, and descending


                g.   Liver:

                     (1)  6 lobes:  right and left lateral, right and left medial, caudate

                            and quadrate.

                     (2)  Cystic duct from gallbladder joins common hepatic duct to

                            form common bile duct.

                h.   Pancreas: 

                     (1)  Divided into cranial and caudal lobes.

                     (2)  Pancreatic duct enters duodenum 7 cm distal to common bile


                i.   Salivary Glands:  4 pairs present




                         Molar (Zygomatic).

                j.   Microscopic Features of GI tract:

                     (1)  Pseudohemosiderosis:  normal accumulation of hemosiderin

                            in the lamina propria of  the villa of small and large intestines.


          8.   Reproductive System

                a.   Male:

                     (1)  Os penis present

                     (2)  Inguinal canal remains open throughout lifetime

                     (3)  Vesicular glands (seminal vesicles):  large, coiled. tubular,

                            long (10 cm)

                         (a)  Intra-abdominal glands

                         (b)  Contain a creamy thick white fluid that forms concretion

                            (vaginal plug) when mixed with coagulating gland secretions.
                    (4)  Other accessory sex glands include:

                          (a)  Coagulating gland: 

                              i)   Duct opens into the calyculus seminalis of the urethra

                              ii)  A small white median papilla which protrudes into the

                                   urethral lumen.

                         (b)  Bulbourethral glands

                         (c)  Prostate


               b.   Female:

                     (1)  Ovaries:

                         (a)  Corpora lutea produced each 16-17 day cycle

                         (b)  Grossly visible as small pink structures.

                     (2)  Vaginal closure membrane:

                         (a)  Usually perforate only at estrus  mid-gestation, and


                     (3)  Cervix:

                         (a)  Each horn of the uterus opens into the cervix

                         (b)  A single os cervix opens to the vagina.

           9.   Urinary System:

                a.   Kidney:  Has a single longitudinal renal papilla with lateral


                b.   External urethral orifice in female opens independently from the

                      vagina onto the  perineum.

           10.  Adrenal Glands:

                a.   Triangular in shape; bilobed; with lateral lobe larger than medial.

                b.   Larger in males than females

                c.   Strain 2's have significantly larger adrenals than outbred stocks

                      (Am.J. Anatomy 63(2):273-295, 1938)
               d.   Are the largest adrenals relative to body weight among animal

                      species; the larger size is due to a thicker cortex  

               e.   Guinea pig and human secrete cortisol as their main

                    glucocorticoid hormone (vs.corticosterone in most rodent species)


      B.   Physiology  (Reference BGP 63-98)

           1.   Hemo-Lymphatic System

                a.   White Blood Cells

                     (1)  Neutrophils    38%

                    (2)  Lymphocytes    55%

                    (3)  Monocytes       3%

                    (4)  Others          4%

                b.   Chemistries

                     (1)  Glucose        60 - 100 mg%

                    (2)  BUN             8 - 20  mg%

                    (3)  Plasma Protein  5.2 - 6.0

                    (4)  Serum Calcium   4.5 - 6.0

                c.   Erythrocytes:

                     (1)  RBC Numbers:  4.5-7.0 x 106/mm3.

                    (2)  PCV:  37-48%.

                    (3)  Mean Corpuscular Vol. (MCV):70.3-85.0

                    (4)  RBC Life Span:  60-80 days

                    (5)  RBC's are fairly fragile.
                    (6)  Hemoglobin:  11.0-15.2 gm/100 ml blood.

                         (a)  Resistant to oxidation by nitrites to methemoglobin (also

                                rat, mouse, hamster, and gerbil) versus species very

                                susceptible to nitrite oxidation (man, monkey, dog, and


                         (b)  Has high oxygen affinity because of high levels of

                                2,3-DPG (as do rat, rabbit, dog, horse, man, and guinea

                                pig) versus those species with low oxygen affinity (cat and


                     (7)  MCHC = 30.5%

                     (8)  Acute hemolytic anemia in response to excess dietary

                          cholesterol (versus cardiovascular lesions in most animals).

                d.   Kurloff Cells:

                     (1)  Unique mononuclear leukocytes containing round or ovoid

                            cytoplasmic inclusions  called Kurloff bodies: from 1-8

                             microns in diameter.

                     (2)  Inclusion is prob. a mucopolysaccharide substance secreted

                            by the cell itself.

                     (3)  Numbers increase markedly during:

                         (a)  Pregnancy

                         (b)  Exogenous estrogen treatment

                         (c)  Increases are rare in fetus and neonates.

                     (4)  0.24% of WBC's in males

                     (5)  Number in females varies with estrous cycle.   

                     (6)  High numbers found in placenta.  They may constitute a

                            physiologic barrier separating fetal antigens from

                            immunologically competent maternal cells

                     (7)  Originate from spleen and thymus

              e.  Lymphocytes:  Lymphomyeloid complex studied because:

                     (1)  The neonatal guinea pig possesses a very mature lymphocyte,

                            similar to human infants

                     (2)  The guinea pig more nearly resembles man imunologically

                            and hormonally than rats and mice  

                     (3)  Cervical thymus is readily accessible for thymectomy /



               f.   Thymus:

                     (1)  At one year, most thymic tissue is involuted with fat deposits.

                     (2)  Thymectomy reduces lymphoid organ weights and produces


                     (3)  Guinea pig (also ferret, monkey and man) is considered a

                            corticosteroid-resistant species because steroid treatment

                            does not readily affect lymphocyte count or thymus.  (Other

                            species respond with decreased thymus weights and

                            lymphocyte counts).


                g.   Bone Marrow:  Guinea pig marrow similar to that of man:

                     (1)  Easily dispensed

                    (2)  Stains well

                    (3)  Actively erythropoietic at birth (unlike rat). 


          2.   Cardiovascular System

                a.   Blood Distribution:

                     (1)  Plasma volume:  3.88% of body weight

                    (2)  Blood volume:  6.96% of body weight

                b.   Heart Rate:  resting (by telemetry) was 275 (229-319) per min

                c.   Blood Pressure:  systolic rarely greater than 100 mm Hg.

                d.   ECG:  similar to human.


          3.   Reproductive Physiology 

                a.   General:

                     (1)  Guinea pig a good animal model because:

                          (a)  It is easy to handle

                         (b)  Has distinct signs of estrus (vaginal membrane opening)

                         (c)  Predictable reproductive behavior.

                     (2)  Most closely resembles woman of all small laboratory

                          animals because:

                         (a)  Has a long cycle (15-17 days)

                         (b)  Ovulates spontaneously

                         (c)  Has an actively secreting corpus luteum.

                     (3)  In the laboratory, guinea pigs are polyestrous, nonseasonal


                b.   Puberty:

                    (1)  Female:  First estrus at 30-134 days (mean 67.8+21.5 SD)

                    (2)  Male:  56-70 days

                c.   Estrous Cycle:

                     (1)  Length:  13-20 days average is 16 days.

                     (2)  Proestrus:  (lasts 1-1.5 days)

                         (a)  Signs include increased activity and vigorous pursuit of


                         (b)  Vigorous mounting in the ten hours prior to estrus.

                    (3)  Vaginal membrane:

                         (a)  Opening precedes estrus

                         (b)  Open for about 2 days during cycle.

                         (c)  Open for average 11 days during 1st cycle; 5 days on

                                future cycles

                         (d)  Closure occurs after ovulation.

                    (4)  Estrus:  (lasts 9-11 hours):

                         (a)  Exhibit copulatory reflex (lordosis or opisthotonos)

                         (b)  Receptivity occurs during darkness. 5 p.m. to 5 a.m.

                    (5)  Ovulation:  Occurs 10 hours after onset of estrus and is


                    (6)  Postpartum estrus: 

                         (a)  Occurs with a 12-15 hours postpartum

                         (b)  Lasts approx. 3.5 hours.

                    (7)  Vaginal Smears:

                         (a)  A better indicator of estrus than vaginal opening. 

                         (b)  Onset of estrus indicated by rounded cornified cells. 

                         (c)  Influx of leukocytes indicates ovulation.

                d.   Hormonal Control of Ovarian Activity:

                    (1)  Corpus luteum (CL):

                         (a)  Secretes progesterone, which increases rapidly after


                         (b)  Luteal cells hypertrophy between days 3 and 9

                     (2)  FSH (follicle-stimulating hormone):

                         (a)  Increases about day 13

                         (b)  This promotes estrogen synthesis by the developing

                    (3)  An LH (luteinizing hormone) surge effects ovulation. 


               e.   Fertilization and Implantation:

                     (1)  Fertilization occurs in fallopian tubes:

                         (a)  Must occur within 20 hours of ovulation.

                         (b)  Usually only 3.4 ova (range 1-5) ovulated.

                     (2)  Implantation: 

                         (a)  8-12 cell stage enters uterus on day 3

                         (b)  Implants on day 6-7.

                     (3)  Postestrus insemination

                         (a)  Within 0-16 hours

                         (b)  Intraperitoneal AI of semen reported to be as successful as

                                natural mating during  estrus.

                f.   Gestation:  (59-72 days; mean = 63 days)

                     (1)  Length is inversely related to number of fetuses carried.

                     (2)  Females may double weight due to fetal mass

                     (3)  Hormonal Control of Pregnancy Involves:

                         (a)  CL of pregnancy continues to grow until day 18-20

                         (b)  CL remains functional throughout the pregnancy. 

                         (c)  Placenta begins endocrine activity after day 15

                         (d)  Pregnancy can be completed subsequent to bilateral

                                ovariectomy after day 21.

                         (e)  Progesterone:  plasma levels increase rapidly after 15 day

                                post-coitus; peak between days 30-45.

                         (f)  Estrogens: Appear at day 20; peak at day 56-60;

                               undetectable following parturition.
               g.   Placentation: 


                    (1)  Discoidal, Labyrinthine Hemomonochorial

                         (a)  Has a single layer fetal capillary membranes that are in

                               direct contact with maternal bloodstream

                         (b)  Very similar to humans. ARM  Hemochorial: also found in

                                rat, mouse, hamster,  rabbit, & armadillo).

                h.   Parturition:

                     (1)  Symphysis pubis begins to relax in response to relaxin

                     (2)  Returns to normal within 24 hours postpartum.

                     (3)  Parturition lasts 10-30 minutes with an average interval

                            between deliveries of 7.4 min (range = 1-16 minutes).

                     (4)  Average age of sow at first litter is 175 days (range 93-420).

                     (5)  Litter Size: Ranges from 1-8; Ave. is 3.

                     (6)  Neonate Viability, Size Growth:

                          (a)  Optimal survival if litter size is 2-4.

                         (b)  Stillbirth incidence increases with size of litter.

                         (c)  Lowest mortality with 69 day gestation.

                         (d)  Asphyxia from fetal membranes a frequent cause of death.

                         (e)  Fetalphagia not observed in the guinea pig.

                         (f)  Stillbirth incidence reported as high as 45% in some

                               colonies;  especially Strain 13's.

                         (g)  Weight at birth inversely related to litter size; average is 80

                                g, 60-130 g range.


               i.   Lactation:

                     (1)  Estrous cycle continues normally after parturition regardless

                           of whether sow is or is not lactating.

                     (2)  Most offspring will survive if no nursing, but weak, runty

                            pigs may result.

                    (3)  Peak lactation period is during days 5-8; agalactia by day

                           18-23, or 24 hours after pups removed.  (Weaning usually at

                           14 - 21 days).

                     (4)  Rate of pup growth directly related to milk yield of sow. 


               j.   Male Reproduction:

                     (1)  Puberty (presence of sperm in semen) at around 10 weeks:

                            sexual maturity (adult  concentrations of sperm) usually not

                             until 14-19 weeks.

                     (2)  Ejaculation occurs in the first or second intromission;

                            followed by a refractory period of one hour before

                            copulation can reoccur.

                     (3)  Electroejaculation has been performed with lumbar and

                            rectal electrodes.

                     (4)  Liquification of coagulated semen can be done with 0.1%

                            chymotrypsin phosphate.

                     (5)  Vaginal plug is the portion of ejaculate secreted by seminal

                            vesicles which coagulates instantaneously on emission

                            (characteristic of ORDER Rodentia).

                            Plug falls out of the vagina a few hours after its formation.

                     (6)  Cobayin is a toxin found in the seminal fluid of guinea pigs. 

                             Produces death in 0.5-2.0 hours when given IP to rabbits.


     C.   Behavior (Ref. BGP pp. 31-52)

          1.   Behavior in the Wild

                a.   C. porcellus, C. aperea, C. cutleri:

                     (1)  Do not dig burrows, but use burrows excavated by other

                            animals, crevices in rocks, or shrubbery.

                     (2)  The alpha male is intolerant of sexual activity by lower

                            ranking males.

                     (3)  Mutual grooming not excessive.


               b.   Diet: 

                     (1)  Green grass and vegetables

                     (2)  Are especially fond of alfalfa

                     (3)  Do not store food


               c.   Activity:

                     (1)  Most active in morning and evening

                     (2)  Little evidence of parental defense of  young

                     (3)  Response to danger is either immobility, or sudden explosive

                           scattering of animals.


          2.   Perception and Individual Behavior Patterns

                a.   Perception

                     (1)  Vision:  Eyes open at birth, but poorly developed depth of

                            vision and object discrimination

                     (2)  Audition:  Maximum sensitivity between 500 and 8000 Hz. 

                            Range:  125-40 or  50,000.

                     (3)  Gustation:

                          (a)  Avoid sweet foods, especially if  more than 0.5M glucose

                          (b)  Reject overly bitter, salty, or chemically pure diets

                     (4)  Other:  Olfaction (pheromones esp.) probably important in



               b.   Activity Patterns:

                     (1)  Under constant illumination, almost continual activity mostly

                            feeding and self-grooming.

                     (2)  Less activity with excessive heat (75-85oF). 


               c.   Responses to Dangers:

                     (1)  "Immobility response":

                          (a)  Tend to freeze in response to un-familiar sudden sounds

                          (b)  A self-protection response; last a few seconds, or up to 20


                          (c)  Electrical shock may also evoke this immobility response;

                                thus not good subjects for pain or shock avoidance studies.

                     (2)  "Scatter Response":

                         (a)  Usually elicited by sudden movements

                         (b)  Involves stampeding in all directions, jumping from a cage,

                              trampling young, or rapid circling.

                     (3)  Preyer reflex: Cocking of the pinna of the ears in response to

                           a short signal from a Galton whistle(clapped hands will work)

               d.   Feeding and Elimination Behavior:

                     (1)  Feeding:

                          (a)  Generally occurs during daylight hours especially at dawn

                                and dusk

                         (b)  Laboratory-reared animals feed both at night and during

                                the day.

                         (c)  Newborn animals can eat solid food within the first day

                                after birth.

                      (2)  Drinking:

                        (a)  With sipper tubes guinea pigs don't lick, draw out water

                                by grasping tube and pulling head back. 

                        (b)  With ball bearing antidrip devices in tubes, gnawing occurs.

                        (c)  With a water dish the head is tilted back after each sip.

                        (d)  Newborns can learn to drink from sipper tube within 48

                               hours of birth.


                    (3)  Elimination:

                          (a)  Newborn guinea pigs usually incapable of voluntary

                                micturition for several days postpartum (up to 1 week)

                         (b)  Maternal licking stimulates both defecation and urination.

                         (c)  Coprophagy  is commonly observed in adults and weanling

                                age young. Usually eat fecal pellets directly from the anus.


               e.   Social Behavior:

                     (1)  Tolerate close physical contact with  each other at rest

                     (2)  Seem to seek contact when moving about

                     (3)  Lactation:  mothers assume a sitting position to allow young

                            to crowd under the mother.
               f.   Grooming:

                 (1)  Little mutual grooming

                 (2)  Self-grooming observed as early as birth; usually after feeding.

                 (3)  Hairpulling is common in pups pulling hair from mother during

                        or shortly after end of lactation.

                 (4)  Hair pulling and ear-chewing can be exaggerated under

                       crowding and stress.


               g.   Communication

                     (1)  Olfactory:

                         (a)  Scent marking with anal glands is common

                         (b)  Males mark with supracaudal gland by rubbing rump.

                     (2)  Auditory:

                          (a)  "chutts" - brief vocalizations (.05sec.); single or paired

                         (b)  "chutter" - 2 to 4 components

                         (c)  "whine" - during flight, discomfort or evasion

                         (d)  Also have whistle, tweet, purr, drr, scream, squeal.


               h.   Dominance Relations:

                     (1)  Conflict arises over space, access to food, drink, objects to

                           gnaw on.

                     (2)  Offensive responses:

                         (a)  Range from vocal response to chasing to deep bite wounds

                         (b)  Male adults:  when caged with females may result in death

                                of the less dominant males


          3.   Reproductive Behavior:

                a.   Mating Behavior:

                     (1)  Male Behavior:  Anogenital investigation by sniffing or

                            licking, mounting with a forepaw clasp, pelvic thrust,

                            intro-mission and ejaculation.

                     (2)  Female Behavior:

                         (a)  Female displays lordosis, wide stance of hind feet, and

                                perineal dilation (opening of vaginal closure membrane).

                         (b)  Estrous cycle:

                            i)   Behavioral estrus is 8 hours

                            ii)  Best indicator of receptivity is lordosis posture in respons

                                to a male or gentle stroking  toward head over rump

                             iii) Occurs nocturnally

                b.   Female Parental Behavior:

                     (1)  Parturition

                         (a)  First pup born after 5 minutes of labor

                         (b) Born head first; the mother then licks and nibbles until fetal

                               membranes are consumed and pup is cleaned. 

                         (c)  Interval between pups usually less than 3-4 minutes

                         (d)  Placenta usually expelled after pups are born; most are

                                eaten by mother or others in pen.

                     (2)  Maternal Solicitude:

                         (a)  Once the dam enters postpartum estrus, shows little

                                interest in  offspring till mating is completed.

                         (b)  Maternal care is limited

                              i)   Passively allows nursing

                              ii)  Neonatal grooming limited to anogenital stimulation.



     A.   Environment

           1.   Temperature

                a.   Optimal temperature range is 65-75oF (17-24oC). Slightly higher

                      for the hairless GP (75 - 79oF)

                b.   Above 90oF may see:

                    (1)  Heat prostration and deaths especially in advanced pregnancy

                    (2)  Abortions

                    (3)  Sterile matings from males

               c.   Poor growth in young if below 55oF (13oC)

               d.   Guinea pigs tolerate cold better than hot temperatures

                e.   Type of caging affects optimal room temperature; i.e., higher

                      temperature needed for wire-bottom cages.

                f.   Control of temperature fluctuations more important that actual

                      temperature as guinea pigs are more sensitive to variations than

                      other laboratory species.

           2.   Relative Humidity:

                a.   40-60% (50% optimal)

                b.   Survival of airborne organisms is lowest at this level. 

           3.   Ventilation

                a.   10-15 air changes per hour.

                b.   Air velocity and direction of flow should be designed to produce

                      a draftless and even distribution of air.

                c.   Auxiliary power should be available for the environmental

                      control system.
          4.   Space requirements for guinea pigs

               a.   Animal Welfare Act

                    (1)  Minimum height:  6.5 inches

                    (2)  Minimum floor space:

                           size         space (square inches)

                          under 350 gm       60

                          over 350 gm        90

                          breeders           180


               b.   NIH ("Guide for the Care and Use of

                    Laboratory Animals, 1985)


                    (1)  Minimum height : 7 in (17.8cm)

                    (2)  Minimum floor space:

                          size          space (square inches)

                         under 350 gm        60

                         over 350 gm         101


          5.   Caging

               a.   Usually constructed of stainless steel,polycarbonate, or plastic.

               b.   Usually in batteries on portable racks (some breeders us fixed

                     tiered compartments, but regular disinfection difficult)

                c.  Solid bottom, bin type cages are most common;especially for

                     breeding animals.

                d.  Wire floors should be welded, rather than interwoven mesh;

                     recommended sizes vary from 1/2" to 1 1/2" square; (smaller size

                     should be avoided to preclude broken legs).

                e.  Tumblebrook cage is commonly used for breeding.  It is a

                    portable 5 cage rack: each solid bottom cage is 30 x 30 x 10 inch
          6.   Bedding

               a.   Peat moss, dried corn cobs, cedar shavings,pine shavings, straw,

                     hardwood chips

               b.   Pine shavings are popular

               c.   Any bedding should be free of dust

               d.   Sawdust has been reported to cause infertility in guinea pigs due

                     to adherence to genital mucosa (vulva or prepuce) and

                     interference with copulation.

                e.   Cereal straw and wood chips may produce upper G.I. (mouth,

                      esophagus) injuries with resultant infection and mortality.


          7.   Cage Sanitation

                a.   High concentrations of mineral salts in guinea pig urine result in

                      accumulation of mineral scale 

               b.   Weekly rotation of acid and alkaline detergents has been

                     effective in removing this scale 

               c.   Should be sanitized, i.e., water heated to 180oF, live steam, or

                    effective chemical disinfectant


     B.   Feeding

           1.   Vitamin C

                a.   Guinea pigs and primates are the only commonly used laboratory

                      animals which require an exogenous dietary source of Vitamin C

                     (ascorbic acid).  Vitamin C is also required by fruit-eating bats

                     and some birds.

                b.   Are unable to convert glucose to ascorbic acid because they lack

                      the microsomal  enzyme L-gulonolactone oxidase.

                c.   Ascorbic acid required to:

                    (1)  Prevent scurvy

                    (2)  Maintain natural disease resistance

                    (3)  To maintain blood complement

                    (4)  Essential coenzyme in the hydroxylase reactions forming

                           hydroxyproline and hydroxylysine, which are components of


                d.   Deficiency results in:

                     (1)  Formation of defective collagen

                    (2)  Enlarged costochondral junctions

                    (3)  Disturbed epiphyseal growth centers

                    (4)  Hemorrhages in various tissues

                    (5)  Delayed wound healing

                    (6)  Impaired bone and tooth formation.


               e.   Daily Ascorbic Acid requirements:

                    (1)  Immature guinea pigs:  0.5 mg/100 g body weight

                    (2)  Maintenance (over 300 g BW):  6 mg

                    (3)  Breeding females:  20 mg


               f.   Sources of Vitamin C:

                    (1)  Commercial Guinea Pig feed:

                         (a)  Feed within 4-6 weeks of manufacture (although under

                               "proper" storage conditions, adequate ascorbic acid levels

                                should be present for 90 days).Commercial feeds usually

                                contain 1000 mg/kg.
                         (b)  Should store at 50oF or less for best preservation of

                               ascorbic acid.

                         (c)  Ascorbic acid deteriorates rapidly; accentuated by heat.

                     (2)  Supplementation with ascorbic acid in drinking water:

                          (a)  Should be added only to distilledor deionized water since

                              chlorinated tap water will inactivate ascorbic acid.

                         (b)  Add at the rate of 200-400 mg/L

                         (c)  Undergoes rapid oxidation and requires frequent

                                preparation (or use of automatic dispenser)

                         (d)  Copper and other metals should not be used in the

                               watering system as they catalyze ascorbic acid. Stainless

                               steel is satisfactory.

                     (3)  Green Vegetable Supplementation:

                          (a)  Kale:

                              i)   115 mg ascorbic acid per 100g

                              ii)  Should be washed in a hyperchlorinated solution to

                                    minimize bacterial contamination.

                         (b)  Carrots, cabbage, sprouted grains,chicory, marigolds have

                                also been used.

                         (c)  Lettuce is a poor source of Vit C.

                         (d)  10-44% average increase in weaned offspring with the use

                                of green vegetable supplements has been reported.


          2.   Feeders: 

               a.   Standard "J" type feeders or wall-mounted feeders with a baffle

                     work well in keeping guinea pigs from climbing into the feeders.

                b.   Bowls are not desirable because guinea pigs tend to sit, sleep and

                      defecate in the bowls.

           3.   Feed Consumption:

                a.   Growing guinea pigs eat about 8% of their body weight in feed

                      daily.  Adults eat about 6% body weight daily 

               b.   Pelleted diets preferred (label and date secondary feed containers

                     to avoid confusing with rabbit chow) 

               c.   Alteration in composition of a feed or introduction of a new feed

                     may result in a sharp decline in feed consumption to the point of

                     starvation or signs of vitamin deficiency occur.


          4.   Protein:

                a.   Have an usually high requirement for certain amino acids

                      (arginine, methionine, and tryptophan)

                b.   Requirements can be met by providing 18-20%protein diet

                      usually of plant origin.


          5.   Roughage:

                a.   Crude fiber should be 13.5% (ILAR, 1967)

                b.   Many breeders advocate feeding hay; may reduce boredom and

                      decrease "barbering"

                c.   Has been reported to decrease hair thinning often associated

                      with late pregnancy.


          6.   Experimental Diets:

                a.   Guinea pigs discriminate between feeds within a few days of

                      birth.  Dietary preparations for nutritional studies should

                      therefore be introduced within a few days of birth.

                b.   Acceptance can be enhanced by pelleting powdered diets in

                      gelatin, moistening feed, or transitory mixing.

      C.   Water


          1.   Requirements (Adults):

                a.   With "greens" supplement - 50-100 ml per day

                b.   Without "greens" supplement - 250-1000 ml per day (excess

                      amount required because of spillage).

           2.   Spillage:

                a.   Occurs because guinea pigs play with sipper tubes and rapidly

                      empty water bottles

                b.   Can be controlled by:

                    (1)  Fitting drinking bottles with ball-bearing equipped sipper


                    (2)  Mounting automatic watering systems slightly (3/4") outside

                          the cage (must adjust valve pressure to prevent water from

                          squirting into the cage).

           3.   Water bowls not recommended because guinea pigs rapidly foul the

                 water with excreta.

           4.   Guinea pigs will blow food and other materials from their mouth up

                 through the sipper  tubes.

           5.   Sipper tubes should be made from stainless steel or other hard

                 material since guinea pigs  chew rather than lick the end of the tube


     D.   Breeding

          1.   Males:

               a.   Fertile matings before 8-10 weeks of age

               b.   Usually mated at 3-5 months (450-600 gm)

               c.   Many breeders mate at weaning.  Efficient reproduction until

                     27-30 months of age.

           2.   Females: 

               a.   First estrus as early as 4-5 weeks of age

               b.   Usually mated between 2.5-3 months of age, or  when reach

                     450-600 gm.

               c.   Should be bred by 6 months of age to lessen likelihood of the


                    (1)  Becoming excessively fat

                    (2)  Having firm fusion of the symphysis pubis, both of which may

                          result in contributing to dystocias or pregnancy toxemia. 

               d.   Efficient reproduction until 27-30 months of age. 

               e.   Females should have produced five or more litters.


     E.   Breeding systems:

           1.   Monogamous pairs:

                a.   One male and one female are mated in a single cage.

                b.   Most commonly used to maintain pedigreed nucleus or

                      foundation colonies of inbred strains which require brother x

                      sister matings.

                \A   Intensive:

                     (1)  Male remains with female throughout parturition and breeds

                           during the postpartum estrus which occurs 3-4 hours after 


                     (2)  Results in an average of 5 litters per year per sow.

                d.   Non-intensive:

                     (1)  Female separated from the male just prior to parturition.

                     (2)  Female bred during the first regularestrus following

                            postpartum estrus.

                     (3)  Results in 3.5 litters per year per sow.


          2.   Polygamous Mating (Harem Breeding)

               a.   Used for outbred production

               b.   One boar mated with 4-6 sows.  Can be maintained as:

                     (1)  Intensive groups:

                          (a)  The group is maintained as a stable colony and held intact

                                throughout their useful breeding life

                          (b)  Maximizes advantage of postpartum breeding and

                                 communal rearing of young

                     (2)  Non-intensive groups:

                          (a)  Sows in advanced pregnancy are isolated either

                                 individually or in groups for farrowing 

                         (b)  After weaning the sows are returned to the mating pens.

          3.   Reproductive Index:  The number of weanlings per female per


                a.   Outbreds: 

                    (1)  Average litter size 3-4

                    (2)  Reproductive index is 1.0 for most commercial breeders

                b.   Inbreds: 

                    (1)  Average litter size 2-3

                    (2)  Reproductive index is 0.7 weanlings per month per female. 

                    (3)  Lower index is attributed to a decline in vigor and fertility

                    displayed by a reduced frequency of farrowing and smaller litters.

           4.   Breeding Colony Mortality:

               a.   Abortions in one report of 8.3%

               b.   Stillbirth incidence increases with larger litters.  Stillbirths are

                     frequent in primiparous animals.

               c.   Other causes include embryonic resorptions, uterine hemorrhage,

                     pregnancy toxemia, dystocias, and exhaustion from prolonged

                     labor are common causes of death in breeding colonies.

           5.   Birth Weights and Growth:

               a.   Depend on nutrition, genetics, a litter size, gestation length, and

                     litter interval.

               b.   Average weight in litter of 3-4 is 85-95 gm

               c.   Young weighing less than 50 g usually die
               d.   Should weigh 165-240 g at 21 days

               e.   Weaning usually between 15-21 days, or 180 g weight

               f.   Gain 2.5-3.5 g per day during first 2 months

               g.   Weight gains slow but continue to 12-15 months of age

                     (1)  Adult sows  700-850 gms

                     (2)  Adult boars 950-1200 gms


     F.   Handling

          1.   The guinea pig is easily excited

          2.   Vocalize frequently when excited

          3.   Should be approached and handled in a gentle quiet manner. 

          4.   Are docile, easily handled and seldom bite. 

          5.   Guinea pigs are very susceptible to stressful situations.

               a.   Transportation and handling may result in significant weight

                     losses (up to 50g) within 24-48 hours. 

               b.   This weight is regained rapidly if conditions are stabilized but

                      may alter experimental data.

          6.   Abortions are not uncommon in late pregnancy following movement

                or frightening events.

          7.   Restraint:

                a.   Should be grasped firmly and quickly around the thorax from

                      above with one hand.

               b.   The thumb should be behind a front leg and fingers forward of

                      the opposite limb.

               c.   As the animal is lifted, the free hand should be placed under the

                     hindquarters to support and control the caudal portion of the

                     body; especially late pregnancy females.

      G.   Sexing

           1.   In young guinea pigs, females exhibit a "Y"-shapedfold in the

                 genital area. The female also has an external urethral orifice

                 separate from and ventral to the vagina.

           2.   Young males have a slit in the anogenital area. The penis is easily

                 extruded from the prepuce with  gently pressure and is located just

                 anterior to  the "slit".


          EM   Note:  the anogenital distance is the same for females and males.


      H.   Identification:

           1.   Multicolored animals may be identified by their natural markings.

           2.   Ear tags:  Not too satisfactory because they are easily torn from the

                 ear or fall out due to ear-chewing by cagemates.  Used successfully

                 by some breeders.

           3.   Ear notching:  Notches may heal closed or the ears become

                 shredded from fighting,  obliterating the notches.

           4.   Ear tatoos:  Use a cutting edge suture needle or special pliers.  Use

                 black ink on white and  green ink on pigmented ears.

           5.   Fur Dyes:

                a.   Used temporarily for up to 6 weeks

                b.   Clean fur with 70% alc to remove fur grease and allow to dry

                c.   Use any of the following solutions, made up in 70%  alcohol:

                     (1)  Saturated picric acid (yellow)

                     (2)  3-5% acidic, basic, or carbol-fuchsin (red)

                     (3)  3-5% methyl or gentian violet (purple)

                     (4)  3-5% brilliant, ethyl, or malachite green

                     (5)  3-5% trypan blue


     I.   Drug Administration

           1.   Intramuscular injections: 

                a.   Give in the posterior lateral thigh 0.5 to 1 cm above the stifle.

                b.   In large guinea pigs, the lumbar musculature, although caution

                      should be exercised.

           2.   Intraperitoneal injections:

                a.   Inject slightly to the right of the midlineabout one inch anterior

                      to the pubis at a low(30o) angle. 

               b.   Elevate rear of animal to shift viscera anteriorly.

           3.   Subcutaneous injections: 

                a.   Easily made in dorsal location (nape of neck).

                b.   The flank mat also be used, but caution should be exercised.
          4.   Intravenous injections:

               a.   Use 23-27 gauge needle. 

               b.   Facilitated by sedation various routes used, including:

                     (1)  Caudal auricular vein (LAS, Feb 1981, pp 85-86)

                     (2)  Cephalic vein

                     (3)  Femoral vein

                     (4)  Lateral metatarsal vein - largest superficial vein

                     (5)  Dorsolateral penile veins

                     (6)  Lingual vein


          5.   Chronically implanted catheters:

                a.   carotid artery

                b.   jugular vein


          6.   Oral Route:

                a.   One report suggest this is easily accomplished by using:

                     (1)  Bulbed needles

                     (2)  5 french infant feeding tubes

                 b.   This may damage the mouth (due to small intrapharyngeal

                       ostium), so use a small syringe and feed the medication per os
     J.   Blood Sampling

           1.   Anterior vena cava (Lab Animal, 11(6): 66-68, 1982)

                a.   Lightly anesthetize guinea pig

                b.   Use 23 gauge, 1 inch needle inserted at notch between

                      manubrium and first left rib

                c.   Yields several cc's blood rapidly

           2.   Femoral Triangle (artery and vein) (LAS, 25(2),1975, pp 216-217)

                a.   Use 23 ga, 3/4 inch needle

                b.   Yield 3 cc or more blood

           3.   Cardiac Puncture:

                a.   Requires light anesthesia

                b.   Insert needle at the intercostal space and apical beat, or lay

                      animal on back and insert at 30o angle in the xiphoid area.

                c.   Should be used as a terminal procedure only.

           4.   Vacuum assisted bleeding (LAS, 25(1), 1975, pp 106-107)

                a.   Nick the superficial surface of the lateral metatarsal vein distal

                      to malleolus.  Coat the leg with silicone grease petroleum jelly.

                b.   Use - 0.5mm Hg vacuum over leg.

                c.   Yields 3 cc blood per minute.


          5.   Orbital Sinus puncture

                a.   Microhematocrit capillary tubes introduced into medical canthus

                      of the eye.

                b.   Should be lightly anesthetized.
          6.   Toenail clipping - small volumes

          7.   Ear Veins:  (LAS, 33(1), 1983, pp. 70-71)

               a.   Punctured with a mechanically-activated lancet: blood collected

                     in capillary tubes

               b.   Allows frequent, multiple small volume samples to be collected


     K.   Anesthesia of Guinea Pigs

           1.   General considerations

                a.   Fasting for 12 hours prior to anesthesia recommended to:

                     (1)  Prevent regurgitation of stomach contents

                     (2)  So that the weight measured just prior to anesthesia is more

                            apt to represent a true value.

                b.   Stage 3 surgical anesthesia plane characterized by:

                     (1)  Flaccid skeletal muscles

                     (2)  Disappearance of reflex responses

                     (3)  Shallow, regular respiration.

                 c.   During stage 3, may exhibit peculiar squirming movements in

                       one leg or entire body which cease spontaneously (additional

                       anesthetic at this point may be fatal).

                d.   Atropine sulfate may be used as a preanesthetic to decrease

          2.   Inhalation Anesthetics:

               a.   Methoxyflurane (Metofane)

                    (1)  Excellent anesthetic for guinea pigs

                    (2)  1% for induction, 0.3% for maintenance

                    (3)  Induction takes 15-18 minutes; recovery10 or more minutes. 

                b.   Halothane, Isoflurane

                     (1)  Considered "high risk" because guinea pigs first hold their

                            breath and then breathe deeply

                     (2)  Halothane:  reported to be hepatotoxic in guinea pigs

                           following repeated dosages.  Causes a 35-40% decrease in

                           blood pressure.

                c.   Administration of Inhalation Agents:

                     (1)  Anesthesia chamber

                     (2)  Nose cone

                     (3)  Bell jar

                     (4)  Endotracheal intubation:

                          EMA  Use a canine otoscope to visualize larynx

                          (b)  A 5 french urinary catheter can be used as a tracheal tube 

                     (5)  Tidal volume of 3.8 ml/kg body weight.


          3.   Injectable Anesthetics:

                a.   Sodium Pentobarbital:

                  (1)  Dose:  28-35 mg/kg I.P. gives 30-100 min of surgical anesthesia.

                  (2)  Should be diluted 50% in normal saline.
               b.   Thiopental (Pentothal):

                    (1)  Dose:  20-55 mg/kg IP; 20 mg/kg IV

                    (2)  Dilute to 1% concentration

               c.   Thiamylal Sodium (Surital):  20 mg/kg IP

               d.   Ketamine Hydrochloride:

                    (1)  Dose:  22-44 mg/kg IM gives excellent sedation for

                          venipuncture, tattooing,etc.

                     (2)  Combine with 5-10 mg/kg xylazine IM to produce light


                     (3)  Surgical anesthesia with 44 mg/kgKetamine plus 5 mg/kg

                           xylazine IM

                     (4)  Self-mutilation has been associated with IM Ketamine in

                            guinea pigs,(IP injection should be considered)

                e.   Fentanyl-Droperidol (Innovar-Vet):

                     (1)  Dose:  0.22 ml to 0.88 ml/kg IM

                     (2)  High dose may produce nerve, vessel, and muscle necrosis

                            and self-mutilation of digits at 7-10 days post-injection.

                     (3)  Causes vasodilation which may aid in venipuncture at

                            peripheral vessels.

                f.   Telazol:

                    (1)  Dose: 10 - 140 mg/lb plus 8 mg\kg IM mixed

                     (2)  Provides good anesthesia for mostprocedures

                     (3)  Gives about an hour of working time
     L.   Antibiotic Therapy

          1.   Many antibiotics apparently cause an alteration in the intestinal flora

                which leads to diarrhea or death within 3-5 days.  Clostridium

                difficile toxin has been suggested as the cause (LAS

                 31(2):156-160, 1981)(Med Micro & Imm 169:187-196, 1981)

           P5   "Toxic" antibiotics include:

             Penicillin,  Bacitracin, Erythromycin, Clindamycin, Lincomycin,

              Chlortetracycline.oxytetracycline, Streptomycin

           3.   "Safe" antibiotics include: (from Williams, C.S.F., 1976): 

               a.   Chloramphenicol palmitate:  60 mg orally daily for 5-7 days

               b.   Chloramphenicol succinate:  10-30 mg/kg BID IM

               c.   Sulfamethazine:  4 ml of 12.5% solution/500 ml of drinking

               d.   Cephaloridine: 10 mg/animal/day

      M.   Euthanasia

           1.   Carbon dioxide in a closed container

           2.   Barbiturate overdose IP

           3.   T-61 Euthanasia Solution


      A.   Background:

           1.   1900-1960's genetic research was concerned with:

                a.   The genetic analysis of coat colors

                b.   The texture

                c.   Studies on the effects of inbreeding.

           2.   Genetic research today is directed at the analysis  of biochemical,

                 physiological and  immunologic characteristics.

           3.   Many mutants that have been described are no longer obtainable.

           4.   Diploid chromosome number is 2N=64, with one pair  sex

                 chromosomes and 31 pairs of  autosomes. 

           5.   Sex determination is xx (female) and xy (male).


     B.   Pigmentation:

           1.   15 loci are known to influence coat color in guinea pigs.  Most are

                 known to have a single  gene mode of inheritance.

           2.   Individual loci:

                a.   Agouti locus (A):

                    (1)  This locus controls amount and distribution of:

                         a     Eumelanin (black or brown pigment)

                         (b)  Phaeomelanin (yellow and reddish pigment) both in

                                individual hairs and in the coat.  Two alleles recognized.

                     (2)  Light-bellied agouti allele (A):  Agouti with light belly.  This

                            is the wild type for Cavia porcellus with terminal or 

                             subterminal yellow band (phaeomelanin) and rest of the hair

                             black or brown (eumelanin).
                    (3)  Non-agouti allele (a):  Eliminates the phaeomelanin band

                           from individual hairs and animals are therefore black (or

                           brown, or variation).

                b.   Brown locus (B):

                     (1)  Wild type allele (B):  Black color (eumelanin)

                     (2)  Brown allele (b):  changes eumelanin in hair, skin, and eyes

                            brown black to brown.  When combined with agouti wild

                            type, a cinnamon-agouti color results.

                c.   Color, or albino locus (C): 

                     (1)  A series of  mutants at this locus  reduces the amount of

                            pigment.  There is no true albino allele homologous to that in


                     (2)  Wild type allele (C):  full pigmentation.  F.e. blacks,

                         reds, golden agoutis.  All of these have black eyes.

                     (3)  Acromelanic albino (ca):  Black(eumelanin reduced to

                           patches on extremities (nose, feet, ears).  Yellow

                          (Phaeomelanin) eliminated completely. Eyes are pink due to

                           lack of pigment in the iris and retina.

                     (4)  The ca allele interacts with the extension allele (e) at the E

                            locus to give a synthetic albino (ca/ca e/e) color in the

                            common laboratory Dunkin-Hartley"albino" guinea pig.


     C.   Pelage Variations:

           1.   Rough (R) locus:  the dominant gene R is necessary for any

                  "roughness" rosette patterns. 

                a.   "Roughness" or rosettes:  this hair pattern is characteristic of the

                      Abyssinian breed and is regulated by four loci.

               b.   The action of this gene is modified by the incompletely dominant

                     genes M and Re.

           2.   Long Hair (l):

                a.   Autosomal recessive character

                b.   Hair length up to 8, 12. or 16 cm at 3, 5, and 7 months

                c.   Peruvian breed:  has long hair (1/1) and rough (R) alleles,

                      resulting in 2 hip rosettes which throw hair forward over head.

                d.   Smooth coated long haired type referred to as "angoras" or





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          Strains of Laboratory Animals, Part 2: Hamster, Guinea Pig, Rabbit,

          and Chicken", Federation of American Societies for Experimental

          Biology, Bethesda, MD, 1979.

     2.  Clark, J.D. and Baker, H.J., The Guinea Pig:  I. Introduction and

          Husbandry (V-6085); II.Biology (V-6086), and III. Diseases (V-6087) 

     3.  Cooper, G. and Schiller, A.L., "Anatomy of the Guinea Pig", Harvard

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     4.  Festing, M.F.W., The Guinea Pig In "The UFAW Handbook on the Care

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          University Press, Ames, IA,1984.

     6.  Manning, P.J., Wagner, J.E., and Harkness, J.E., Biology and Diseases

          of Guinea Pigs, In "Laboratory Animal Medicine", Fox, J.G., Cohen,

          B.J., and Loew, F.M., eds, pp. 149-181 Academic Press, 1984.

     7.  National Academy of Sciences, National Research Council, Institute of

          Laboratory Animal Resources, "Guide for the Care and Use of

          Laboratory Animals", Nat Academy of Sciences, Washington,1985.

     8.  Obeck, D.K., The Guinea Pig, In:  Aeromedical Review 4-74, Selected

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          Aerospace Medicine, Brooks Air Force Base, TX, 1974.

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          and Rodents", 2nd ed. Lea and Febiger, Philadelphia, 1983.

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           Pig", Academic Press, NY (1976).

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            Mosby Co., Saint Louis, MO, 1976.

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     14.  Charles Rivers Update, "Euthymic Hairless Guinea Pigs for

            Dermatological Studies". Vol 1,Number 2, Spring 1986

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            International, Waverly, Pa. July 1987

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