|THE GUINEA PIG:
BIOLOGY, CARE, IDENTIFICATION,
NOMENCLATURE, BREEDING, AND
USAMRIID Seminar Series
17 February 1989
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A. History and Origin
1. Origin of the guinea pig is unclear.
a. Wild guinea pig is Cavia aperea
b. Widely distributed in Argentina, Uraguay, and
c. Cavia cutleri is still wild in Peru
2. Spanish found Andean Indians had domesticated
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
5. 1500's: Dutch sailors introduced the guinea pig
6. 1770's: Probably reached the United States as
pets and fancy animals.
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
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
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
"squirrel-like" ... such as
squirrels, marmots, gophers,
beavers, and Kangaroo rats and
the suborder Myomorpha: "rat-
like" ... house mouse, norway
rat, hamsters, voles, gerbils,
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)
a. Short, smooth, straight hair (3.8 cm)
b. Solid colors: albino, white, black, agouti,
sandy, red, chocolate, cream, etc.
c. Bicolored and tricolored animals also.
d. Most inbred and outbred laboratory guinea
pigs are the English variety.
a. Short, course hair that radiates from
multiple centers on the body to form
b. Variety of colors.
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:
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
(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 in 1953.
(2) "Waltzing" or circling and deafness
develop due to atrophy of organ of Corti
(3) Inherited as an autosomal dominant gene
with full penetrance.
(4) Homozygous condition results in high
c. Hairless and Immunodeficient Mutant (LAS
29(6): 744-748, 1979):
(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
(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
(4) No grossly visible thymic tissue, cystic
spaces found where thymus should have
been. Germinal follicles reduced or
absent in lymph nodes and intestinal
(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
(2) Hair bulb, erector pili, and sebaceous
glands do exist.
(3) Produces defective hair shaft
(4) Reduced number of shafts
(5) Normal functional thymus
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
(3) Sudoriferous glands absent
(4) 5-6 rows of tactile hair (vibrissae) on
(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
(2) A single large papillary duct opens to
2. Dental Formula:
1 01 3
2(I-C-PM-M-) = 20 teeth.
1 01 3
a. Diastemal space between incisors and
b. A11 teeth continue to grow for lifetime of
c. The molars are hypsodontic = prism shaped
teeth with high crowns
d. With medial inclinement of the teeth and
continuous growth, encasement of the tongue
e. Only one set of teeth (monophydont)
a. Vertebral formula:C7,T13-14,L6,S2-3,Co4-6
6 sternebrae. 13 or 14 pairs of ribs:
7th-9th contribute to costal arch
10th-14th are floating
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
(3) The pubic symphysis degenerates 2 weeks
prior to parturition resulting in
complete destruction by parturition
(4) Palpation of separation can be used to
4. Muscular System
a. Well developed masticatory muscles (Masseter
b. Reflects the gnawing behavior and
corresponding mastication by grinding (versus
5. Cardiovascular/Respiratory System
(1) Soft palate is continuous with base of
the tongue and lateral walls of the oral
(2) Opening into larynx is a small
intrapharyngeal ostium (AALAS Abstract
(1) 3 left lobes (cranial, middle, caudal)
and 4 right lobes (cranial, middle,
(2) Pleural cavities are continuous (LAS
16(5): 411, 1966)
c. Arteries: 3 deviations from normal mammalian
vascular pattern (Amer. J. Anat. 139, 269-
(1) There may be 2 or 3 pairs of renal
arteries (versus normal 1 pair in most
(2) The abdominal aorta gives rise to a
celiomesenteric trunk instead of
separate celiac and cranial mesenteric
(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
(2) In adults may be completely gone or
persist in caudal cervical or cranial
(3) Thymic tissue is replaced primarily with
fat as age progresses.
(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 or fused to it (Cooper
and Schiller, 1975).
(7) Guinea Pig used extensively for
immunologic studies because the cervical
thymus is easily removed (LAS 25, 82-84,
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
(1) Rostral one-third is free.
(2) Remainder attached to floor of oral
(3) Small filiform papillae anteriorly,
large fungiform papillae posteriorly.
(1) No keratinized non-glandular portion
present i.e., all glandular.
c. Small Intestine:
(1) About 125 cm (50 in) in length
(2) Common bile duct enters duodenum 1 cm
caudal to pylorus.
(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
(5) Produces out-pouchings called haustra.
e. Peyers patches:
(1) About nine flat white 1 mm diameter area
of lymphocyte aggregates on mucosal
(1) Ascending, spiral ascending, transverse,
and descending portions.
(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
(1) Divided into cranial and caudal lobes.
(2) Pancreatic duct enters duodenum 7 cm
distal to common bile duct.
i. Salivary Glands: 4 pairs present
j. Microscopic Features of GI tract:
(1) Pseudohemosiderosis: normal
accumulation of hemosiderin in the
lamina propria of the villa of small and
8. Reproductive System
(1) Os penis present
(2) Inguinal canal remains open throughout
(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
(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
(b) Bulbourethral glands
(a) Corpora lutea produced each 16-17
(b) Grossly visible as small pink
(2) Vaginal closure membrane:
(a) Usually perforate only at estrus
mid-gestation, and parturition.
(a) Each horn of the uterus opens into
(b) A single os cervix opens to the
9. Urinary System:
a. Kidney: Has a single longitudinal renal
papilla with lateral calyces.
b. External urethral orifice in female opens
independently from the vagina onto the
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-
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%
(1) Glucose 60 - 100 mg%
(2) BUN 8 - 20 mg%
(3) Plasma Protein 5.2 - 6.0
(4) Serum Calcium 4.5 - 6.0
(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 ruminants)
(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
(2) Inclusion is prob. a mucopolysaccharide
substance secreted by the cell itself.
(3) Numbers increase markedly during:
(b) Exogenous estrogen treatment
(c) Increases are rare in fetus and
(4) 0.24% of WBC's in males
(5) Number in females varies with estrous
(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 (LMC)
(1) The neonatal guinea pig possesses a very
mature lymphocyte, similar to human
(2) The guinea pig more nearly resembles man
immunologically and hormonally than rats
(3) Cervical thymus is readily accessible
for thymectomy / modification.
(1) At one year, most thymic tissue is
involuted with fat deposits.
(2) Thymectomy reduces lymphoid organ
weights and produces lymphopenia.
(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
g. Bone Marrow: Guinea pig marrow similar to
that of man:
(1) Easily dispensed
(2) Stains well
(3) Actively erythropoietic at birth (unlike
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 minute.
c. Blood Pressure: systolic rarely greater than
100 mm Hg.
d. ECG: similar to human.
3. Reproductive Physiology
(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
(3) In the laboratory, guinea pigs are
polyestrous, nonseasonal breeders.
(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 cagemates
(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
(b) Receptivity occurs during darkness.
5 p.m. to 5 a.m.
(5) Ovulation: Occurs 10 hours after onset
of estrus and is spontaneous.
(6) Postpartum estrus:
(a) Occurs with a 12-15 hours
(b) Lasts approx. 3.5 hours.
(7) Vaginal Smears:
(a) A better indicator of estrus than
(b) Onset of estrus indicated by
rounded cornified cells.
(c) Influx of leukocytes indicates
d. Hormonal Control of Ovarian Activity:
(1) Corpus luteum (CL):
(a) Secretes progesterone, which
increases rapidly after ovulation.
(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 follicle.
(3) An LH (luteinizing hormone) surge
e. Fertilization and Implantation:
(1) Fertilization occurs in fallopian tubes:
(a) Must occur within 20 hours of
(b) Usually only 3.4 ova (range 1-5)
(a) 8-12 cell stage enters uterus on
(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
(2) Females may double weight due to fetal
(3) Hormonal Control of Pregnancy Involves:
(a) CL of pregnancy continues to grow
until day 18-20
(b) CL remains functional throughout
(c) Placenta begins endocrine
(Progesterone) activity after day
(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
(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, &
(1) Symphysis pubis begins to relax in
response to relaxin
(2) Returns to normal within 24 hours
(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
(b) Stillbirth incidence increases with
size of litter.
(c) Lowest mortality with 69 day
(d) Asphyxia from fetal membranes a
frequent cause of death.
(e) Fetalphagia not observed in the
(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.
(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
(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