Nomenclature, breeding, and



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THE GUINEA PIG:
BIOLOGY, CARE, IDENTIFICATION,

NOMENCLATURE, BREEDING, AND

GENETICS

Ron Banks

USAMRIID Seminar Series

17 February 1989


NOTE: A shaded statement indicates that an ACLAM boarded

indivigual has identified that material as having a high

probability of being on the boards, or having been on past

boards! Use this material as a starting point for study.


I. INTRODUCTION
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

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 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

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

squirrels, 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, cream, etc.

c. Bicolored and tricolored animals also.

d. Most inbred and outbred laboratory guinea

pigs are the English variety.

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 in 1953.

(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 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

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


II. BIOLOGY
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 crowns

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 (AALAS Abstract

#96, 1983)
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 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,

1975).

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 anteriorly,

large fungiform papillae posteriorly.
b. Stomach:
(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.


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 portions.


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 duct.


i. Salivary Glands: 4 pairs present

Parotid


Mandibular

Sublingual

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 parturition.
(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 calyces.


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

rabbit)


(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

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 (LMC)

studied because:


(1) The neonatal guinea pig possesses a very

mature lymphocyte, similar to human

infants
(2) The guinea pig more nearly resembles man

immunologically and hormonally than rats

and mice
(3) Cervical thymus is readily accessible

for thymectomy / modification.


f. Thymus:


(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

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 minute.


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 breeders.
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 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

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 spontaneous.


(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 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

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

(Progesterone) 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

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