Guinea Pig

GUINEA PIG (more correctly overseas pig), Cavia, Cobaya Marcgr., s. Porcellus L., a rodent from the family Caviidae, resp. Subungulata; the guinea pig is one of the most commonly used laboratory animals (see). In English works it is called guinea-pig or cavy, in French—cochon d'Inde or cobaye, in German—Meerschweinchen, in Italian—porcella d'India. The homeland of the guinea pig is Peru. Its wild ancestor is Cavia Cutleri. Zoological relatives: paca, agouti, capybara, mara. Introduced to Europe from America in the 16th century. Body length of an adult guinea pig is 250–300 mm, weight 500–900 g. It is impossible to determine the exact age of a guinea pig by weight, as birth weight varies among different individuals (in the Moscow Zoo—from 32 to 130 g). The approximate ratios of age, weight, and length under ordinary conditions of housing and feeding are as follows (from Livon): Age | Weight (in g) | Weight (in g) | Length (in mm) At birth | 60–80 (avg. 74 g) | 50–100 15 days | 170–200 | 150–200 1 mo. | 240–250 | 250–300 2 mos. | 350–400 | 350–400 3 mos. | 450–500 | 400–500 4 mos. | 550–600 | 500–600 6 mos. | 650–700 | 600–700 | 700–800 | 800–900.

Anatomy. On the forelimbs there are 4 toes, on the hindlimbs 3 toes, armed with broad, short claws ribbed in front, resembling tubular hooflets; the sole is bare with strongly keratinized skin. There is no tail.

Dental formula: 1/1, 0/0, 1/1, 3/3.

The articular fossa on the skull for the lower jaw has the form of a longitudinal groove. The articular head of the mandible resembles a semi-cylinder with an axis running from back to front; this causes considerable mobility of the lower jaw forward and backward. The chin symphysis remains open for a long time, becoming immobile only in old individuals. There are 36–37 vertebrae (7 cervical, 13 thoracic, 6 lumbar, 4 sacral, 6–7 caudal). There are 13 ribs (6 true + 7 false). The sternum consists of 5 parts that fuse late. Large salivary glands (especially gl. submaxillaris), a bulky liver, a large cecum, small thyroid glands without an isthmus, and very bulky adrenal glands. There are horny denticles on the mucous membrane of the penis pocket. At the end of the glans penis are 2 styloid horny formations (epidermal horns, cornes epidermiques of Lipschütz, 1924), about 0.5 mm long up to the age of 1 month and 3.0–5.5 mm at over 6 months of age; after castration, the horns become thinner and shorter, lose elasticity, and together with the penis become covered with a cheesy secretion (Lipschütz, 1924; Vorontsova, 1926). Physiology. Erythrocytes about 5,900,000, leukocytes about 15,000, platelets about 100,000. Leukocyte formula: 46.5% lymphocytes (13.5% large, 33% small), 38.5% neutrophil type, 13% eosinophils, 0.85% basophils, 0.5% mononuclears, 0.65% transitionals. Hemoglobin 96% (according to Sahli). Heart rate 150–160 beats per minute, cardiac impulse weak, diffuse. Respiration rate 80–85. There are no respiratory changes in heart rhythm; each heartbeat is synchronous with 2 respiratory movements. Temperature 39.0–39.7°. The amount of urine from a guinea pig weighing 600 g = 52 cm³, from a guinea pig weighing 100 g = 8–16 cm³ per 24 hours. Specific gravity of urine 1.033–1.036. Per 100 g of body weight, 0.45–0.52 g of dry urine residue is produced, with a high mineral content in the solid residue = 58.44 (in humans, 30–35). Excrement per 100 g of body weight per 5.9 g of food consumed accounts for 0.857 g of dry matter. The guinea pig is strongly predisposed to epileptoid convulsions. The guinea pig responds extremely easily to the most insignificant external stimuli with disturbances of respiration, blood circulation, digestion, body temperature, and a decrease in appetite. Breeding. Gestation is 65–67 days. In a litter, there are 1–3 pups, less often 4–6. Pups are born fully furred and begin eating adult food 3–4 days after birth. Sexual maturity occurs before the end of growth: in males at 2½–3 months, in females at 1–2 months. Breeders usually do not use them for breeding before 5–6 months. Guinea pigs begin to reach full size by 6–8 months and often finish growing by 1–1¼ years. It is better to separate pregnant females at mid-gestation. Growth continues uninterruptedly during subsequent pregnancies. The guinea pig lives up to 4–5 years, in exceptional cases up to 6–8 years. Males are polygamous and aggressive toward each other; if kept together from an early age they are calmer; castration often does not eliminate the sexual instinct and aggressiveness. Feeds—see Laboratory Animals. Breeds in the true sense of the word are absent in guinea pigs. Three groups of guinea pigs are distinguished: smooth-haired, long-haired (Angora or Peruvian), and rosetted (abyssinian, rough-haired, or crest-coated); the latter are usually considered poorly suited for medical purposes. Within the three groups, varieties of all colors are observed (see below). Genetically, along with the rabbit and the mouse, the guinea pig is among the best-studied laboratory animals. The genetics of the guinea pig has much in common with the genetics of the rabbit. Knowledge of guinea pig genetics is necessary for physicians: 1) due to the presence in guinea pigs of hereditarily conditioned resistance to tuberculosis and certain biochemical properties of the blood that are important for immunological work; 2) for a genetically conscious attitude toward experimental animals in connection with widespread opinions regarding the varying lability of guinea pigs of different coat colors. 1. Genetics of coat color and pattern. The following allelomorphs (see) are well established in the guinea pig: I. C > c^k > c^d > c^r > c^h. Albino series: C—full, intense coloration; c^k—slight weakening of black and significant weakening of red pigment; c^d—significant weakening of black and red; c^r—“non-yellow”: yellow and red areas of the skin are replaced by white, black is slightly weakened, eyes reflect a red, ruby glow; c^h—ermine coloring, acromelanism (Wright, 1925; Ilyin, 1926). II. A > a^r > a. A—zonal, so-called “agouti” hair coloration, yellow belly; a^r—zonal hair coloration, gray, zonal belly; a—non-zonal hair coloration. III. B > b. B—black pigment, b—brown pigment. IV. F > f. f—yellow attenuator and red intensifier; its action increases with age. F—its normal allelomorph. V. E > e^p > e. E—full distribution of black and brown pigment over the pigmented skin; e^p—partial distribution of black or brown pigment: “tortoiseshell”, black-and-yellow guinea pigs; e—complete non-distribution of black or brown pigment: solid red or yellow guinea pigs. VI. S > s. S—solid-colored, without white spots; s—white-spotted. Aside from these well-established allelomorphs, there are as yet not fully proven indications of the existence of the following additional factors (Ibsen, 1925): 1) a yellow intensifier increasing in action with age: guinea pigs born cream-colored become dark yellow with age; apparently epistatic over the IV gene; 2) gene for white tips of hairs—affects only brown hairs; dominant, heterozygotes are intermediate; 3) gene for black tips of hairs—acts only 6–8 months after birth, discovered in red and yellow guinea pigs. 2. Genetics of eye color. VII. P > p^r > p. P—black eyes; p^r—ruby eyes, which does not prevent the manifestation of yellow spots, intensity of coat color is unchanged (cf. ruby eyes during color weakening under the action of the “non-yellow” gene); p—pink eyes, black coat color is weakened to coffee-gray (chocolate). VIII. Sm > sm. sm—“salmon” eyes: outwardly pink, but having a small amount of dark pigment surrounding the pupil; the sm gene manifests its action only in the presence of the p gene, over which it is epistatic. Sm—normal allelomorph that does not prevent the action of the P and p genes. 3. Genetics of coat structure. IX. L > l. L—short-hairedness, l—long-hairedness (Angora hair). X. R > r. R—rosetted or rough-hairedness, r—smooth-hairedness. XI. M > m. M—modifier of rough-hairedness, inhibiting its full expression; m—full development and spread of rough-hairedness on the back and head. 4. Genetics of structural and morphological traits in guinea pigs have been studied relatively little; hereditary traits of this kind include dwarfism, polydactyly (4 digits on the hind legs instead of the normal 3), cyclopia, and hypermastia (normal is 2 mammae); manifestation of otocephaly in connection with hereditary traits was also pointed out, but its genetics is poorly studied. 5. Genetics of physiological and pathological properties. 1) Absence of complement in blood serum (Hyde, 1923), as a result of which guinea pig serum is unable to hemolyze horse, sheep, or human blood cells; a simple recessive trait not sex-linked (Mendelizes well). 2) Altered catalase content in the blood (Koltzoff, Elizarova). Four types have been established: a) almost complete absence of catalase; b) Bach catalase indices 2–6; c) catalase index 8–13; d) catalase index 12–20. The first two types are easily fixed through inbreeding; probable genetic formulas: type I—aabb; type II—aaBB; type III—AaBB; type IV—AABB. 3) Paralysis agitans, not identical to the human disease of the same name and showing a number of features of similarity to paralysis agitans, chorea festinans, aplasia axialis extracorticalis congenita, paramyotonia congenita, degeneratio progressiva lenticularis, etc. Average birth weight is the same as in normal guinea pigs. Intensity of symptom expression varies; the disease ends fatally, usually at about 2 weeks of age. A simple recessive trait not sex-linked (excellent Mendelian ratios). Dominance of the normal state is complete, heterozygotes are completely healthy (Cole, Ibsen, 1920). 4) High resistance to tuberculosis was discovered in certain lines of guinea pigs (Wright, Lewis, 1921). The gene determining resistance to tuberculosis is dominant over the gene for easy susceptibility; the presence of additional factors in individual lines is possible; these genes are independent of other factors that determine the viability of guinea pigs. 5) A number of traits of viability and development of guinea pigs are hereditary, such as litter size, number of litters per year, number of pups per year, percentage of stillbirths, birth weight, growth rate, etc.

N. Ilyin. The importance of the guinea pig is varied. In their homeland, they are used for food; their pelts are used for various crafts (fur, bookbindings, leather, etc.); in live form, guinea pigs serve genetic purposes and as widely and variously used laboratory animals. They are used in physiology, pharmacology, experimental pathology, pathological anatomy, bacteriology, parasitology, in infectious and therapeutic clinics, and diagnostic laboratories. It is easily infected with tuberculosis, diphtheria, typhoid, paratyphoid, typhus and relapsing fever, tick-borne typhus, syphilis, rabies, sodoku, infectious jaundice; reacts to infection with scarlet fever. In addition, it becomes infected with anthrax, glanders, foot-and-mouth disease, dysentery of calves, Bacillus abortus of Bang, trypanosomes, etc. In experimental helminthology, it serves to study the migration of larvae of roundworms and trichinae. It can serve, although with difficulty, to feed lice (Pediculus). It is convenient for feeding bedbugs, fleas, certain ticks (e.g., Ornithodorus papillipes), and other ectoparasites. Diseases of the guinea pig: described by various authors, pneumonia infectiosa caviarum with Bact. pneumoniae caviarum, Bacillus pulmonum caviarum glutinosus, and diplococcus isolated during it; epizootic disease (with severe nasal discharge and heavy coughing); colibacillosis caviarum with Bacillus caseolyticus; paratyphoid B; fibrinous inflammation of serous membranes; pyaemia caviarum with Diplococcus lanceolatus; hemorrhagic septicemia; paralysis meningo-myeloencephalitis infiltrativa with tonic-clonic convulsions, caused by a filterable virus; plague; tuberculosis; pseudotuberculosis (pseudotuberculosis caviarum) with Bacillus pseudotuberculosis rodentium, etc. Avitaminosis: in the absence of vitamin C in food (green fodder, vegetables), a scurvy-like disease with ulcerations of the jaws and paralysis of the hind limbs occurs. Parasites of the guinea pig. Among ectoparasites there are: biting lice Gyropus ovalis, Gyropus porcelli; Menopon extraneum; larvae of parasitic flies; among mites: Sarcoptes scabiei var. cuniculi. Endoparasites: Protozoa—Flagellata: Oikomonas termo from guinea pig feces; Sphaeromonas communis, Selenomonas palpitans (=S. ruminantium) in the cecum; Enteromonas fonsecai; Chilomitus caviae in the cecum; trypanosomes morphologically similar to Trypanosoma lewisi (e.g., Tr. bandicotti, causing fatal infection); Trichomonas caviae in the cecum and colon (causes epizootic disease); Eutrichomastix caviae in the cecum; Embadomonas intestinalis in the same place; Chilomastix intestinalis.—Sarcodina: Entamoeba cobayae and E. caviae, both of the E. coli type; Endolimax caviae.—Sporozoa: coccidia—a variety of Eimeria perforans (liver and intestines), causing coccidiosis, which sometimes results in significant mortality; E. caviae—in the large intestine; blood sporozoans—Toxoplasma caviae; the coccidian Klossiella cobayae in the renal tubules and in the endothelium of blood vessels; Pneumocystis carinii from the lungs of the guinea pig may also belong to this same species.—Infusoria: Cyathodinium conicum, C. vesiculosum, C. piriforme, and Cunhaia curvata in the cecum of wild guinea pigs; Balantidium caviae.—Spirochetes: Cristispirella caviae from the small intestine; a form similar to Spirochaeta raillieti (the causative agent of relapsing-like fever of rabbits in Tonkin) was found in the blood of guinea pigs.—Worms: Trematoda—Fasciola hepatica; Cestoda—Hymenolepis fraterna and Taenia pisiformis (Cysticercus pisiformis in the mesentery); Nematoda: Syphacia obvelata and Trichocephalus muris (=nodosus) in the cecum; Physaloptera muris brasiliensis in the stomach. Arthropods: Linguatula serrata—larvae of the "tongue worm" in the mesenteric lymph nodes. Tumors of the guinea pig: sarcoma (large-cell, spindle-cell)—transplants well; adenoma-like formation in the lungs.—Operations on the guinea pig: blood collection from the vessels of the auricle, jugular veins, femoral artery, or by heart puncture; liver puncture near the spine in the third (counting from behind) intercostal space; bone marrow is obtained by puncture of tubular bones (in large guinea pigs) or (better) trepanation of the tibia; infection with infectious and invasive agents is performed: a) by injections under the skin, into the abdominal cavity, into the thoracic cavity (through the right fourth intercostal space), into the heart cavity, into the veins (v. jugularis, veins of the lower leg), into the cranial cavity (along the line connecting the posterior angles of the eyes), into the trachea, into the gallbladder, into intestinal loops, into the testicle, into the mammary gland, into the spinal canal, into nerve trunks, into the knee joint, into the anterior chamber of the eye; b) through a thin catheter—into the rectum, stomach, urinary tract; c) by inhalation; d) with food and drink; e) by applying the virus to scarified skin or cornea, to intact skin or conjunctiva of the eye, mucous membrane of the oral cavity and nasal cavity. A guinea pig can bite a human; in the case of a bite by an infected guinea pig, immediate intervention of an antiseptic or special therapeutic nature is necessary, depending on the property of the virus (rabies, tuberculosis, syphilis, etc.).

E. Pavlovsky