n-6 Fatty Acids

Reid et al. (1964) conducted several studies to assess the requirement for n-6 fatty acids. In one experiment, they measured the appearance of dermatitis (a sign of EFA deficiency) in young male guinea pigs. These animals were fed diets containing 0, 0.17, 0.33, 0.67, 1.33, or 4.0 g methyl linoleate and 10 g corn oil/kg. The diets were found to actually contain 0.15, 0.20, 0.24, 0.34, 0.54, 1.31, and 1.89 percent, respectively, of the calories as linoleic acid after accounting for the linoleic acid supplied by the cornstarch. Dermatitis occurred until the concentration of linoleic acid in the dietary treatment reached 1.31 percent of calories; thus, the amount of linoleic acid needed to prevent dermatitis falls between 0.54 and 1.31 percent of total calories. Guinea pigs grew normally when the concentration was only 0.24 percent. Thus, a higher concentration of linoleic acid is required to prevent dermatitis than is needed for normal growth.

Reid et al. (1964) also measured the requirement for linoleic acid by measuring the triene:tetraene ratio [20:3(n-9) to 20:4(n-6)] in erythrocytes in response to increasing concentrations of dietary linoleic acid, a method developed previously by Holman (1960) for rats. The requirement for linoleic acid was estimated as the percentage of the total calories of linoleic acid at the breakpoint of this dose-response curve. The actual dietary treatments provided 0.15, 0.46, 0.88, 1.04, 1.25, and 1.42 percent linoleic acid (supplied by safflower oil). Based on this method, the linoleic acid requirement for guinea pigs was determined to be between 0.88 and 1.04 percent of total calories.

n-3 Fatty Acids

As in other mammals, in the guinea pig n-3 fatty acids concentrate in certain tissues, including brain and testes (Tinoco, 1982), but the precise function of these fatty acids is unknown. Unlike most other mammals, however, the guinea pig has been found to have relatively lower concentrations of 22:6(n-3) and higher concentrations of 22:5(n-6) in their photoreceptor outer segment membranes. This may, in part, explain the absence of changes in the electroretinogram (a measure of retina function) of offspring of guinea pigs fed sunflower oil [high linoleic acid 18:2(n-6), very low α-linolenic acid 18:3(n-3)] treatments for several generations (Leat et al., 1986). Neuringer et al. (1988) speculated that the shift in fatty acid composition of the retina as a result of n-3 fatty acid-deficient diets may affect retinyl function less than in other species that maintain higher concentrations of retinal 22:6(n-3). Essentiality of n-3 fatty acids in the diet of the guinea pig has not been studied.

Signs of EFA Deficiency Classic signs of EFA deficiency (lack of n-6 fatty acids) were reported by Reid (1954b) and Reid and Martin (1959) and include ulcers about the neck and ears, loss of hair on the ventral surface, retarded growth, dermatitis, and mortality. They described additional signs of priapism; underdevelopment of the spleen, testes, and gallbladder; and enlargement of the kidneys, liver, adrenals, and heart. Specific skin changes were found to be confined to the surface layers and, therefore, less extensive than those of the EFA-deficient rat. Fat deprivation was not found to increase water consumption, which also is in contrast to signs described in the EFA-deficient rat.

Reproduction

Although amino acid requirements for the pregnant/lactating and nonpregnant/nonlactating adult guinea pig have not been specifically determined, natural-ingredient diets that provide 18 to 20 percent protein result in satisfactory reproduction (Lister and McCance, 1965; Shelton, 1971) and maintenance of adults (Shelton, 1971). Apgar and Everett (1991b) obtained adequate and similar weight gains and reproductive performance in pregnant guinea pigs fed either a casein-agar diet containing 300 g casein/kg without added arginine or a commercial plant protein diet containing 185 g protein/kg diet, but fewer neonates from dams fed the casein-agar diet survived. These investigators suggested that the cecal flora as a possible source of essential or unrecognized nutrients may be more critical during pregnancy than during growth. In addition, it has been suggested that the elimination of waste products by the pregnant guinea pig is less difficult when an adequate but not excessive amount of protein is provided. Pregnant guinea pigs often have a fetal mass approaching the nonpregnant weight of the female, possibly making elimination of waste products difficult.

Maintenance

The adult nonpregnant, nonlactating guinea pig's requirement for protein and amino acids may be lower than the amount required for growth. The requirement may be similar to that reported for 770 g males (Schiller, 1977). Nitrogen balance and body weight were maintained when a crystalline amino acid diet containing 11 g indispensable amino acid nitrogen/kg and 25.6 or 18.2 g total nitrogen/kg diet (equivalent to 160 or 114 g crude protein/kg diet) was fed but not when the diet contained 11 g total nitrogen/kg (equivalent to 69 g crude protein/kg).

Signs of Protein and Amino Acid Deficiency Protein deficiency produced in growing guinea pigs fed a diet containing 30 g casein/kg diet for 3 to 4 weeks causes growth retardation, marked reduction in plasma total protein and albumin, profound alterations in the plasma amino acid profile, and mild fatty liver. These animals develop clinical symptoms similar to the Kwashiorkor syndrome, including reduced activity, mild hair loss, and extensive edema of the face and forelimbs (Enwonwu, 1973). A protein deficiency produced in growing guinea pigs consuming 20 g casein/kg diet was accompanied by marked inhibition of local and systemic immune responses to vaccination with bacillus Calmette-Guerin (Bhuyan and Ramalingaswami, 1973). Enwonwu (1973) suggests that guinea pigs are suitable models for the study of human protein-calorie malnutrition.

Reports of protein deficiency produced by lowering the protein content of diets fed to adult guinea pigs during reproduction or maintenance were not found. Reducing the intakes of both protein and energy by restricting the intake of adequate protein diets (300 g casein or 185 g plant protein/kg) to 20 to 50 percent during the last half of gestation resulted in premature delivery, reduced weight for pups, and death of most pups within the immediate postnatal period (Apgar and Everett, 1991b). Reduced litter size was reported when feed was restricted to 40 percent of normal ad libitum intake beginning at day 30 of gestation (Young and Widdowson, 1975).

Calcium and Phosphorous

The calcium, phosphorus, potassium, and magnesium requirements of the guinea pig, like those of the rat, appear to reflect interactions among these elements. Morris and O'Dell (1961, 1963) and O'Dell et al. (1956, 1960) found that adequate dietary concentrations of calcium (8 to 10 g Ca/kg), phosphorus (4 to 7 g P/kg), magnesium (1 to 3 g Mg/kg), and potassium (5 to 14g K/kg) varied as the concentrations of the other three elements varied. Van Hellemond et al. (1988) observed that guinea pigs fed purified diets containing 8.4 g Ca/kg with 7.7 g P/kg and 1.0 g Mg/kg retained more calcium than those fed the same concentrations of calcium but with less phosphorus (4.4 g P/kg) and more magnesium (1.9 g Mg/kg). Thus 8 g Ca/kg and 4 g P/kg diet will meet requirements for these minerals.

There is no obvious physiological explanation for the higher apparent requirement of guinea pigs than rats for calcium and phosphorus. Further work is needed to assess growth and bone and kidney accumulation of calcium when guinea pigs are fed concentrations of calcium and phosphorus more consistent with those recommended for rats.

Signs of Calcium and Phosphorus Deficiency Signs of calcium deficiency have been produced in young guinea pigs fed a purified diet containing 0.28 g Ca/kg, 0.20 g P/kg, and a low concentration of vitamin D (Howe et al., 1940). Nine of 21 animals fed this diet survived for 60 days. These guinea pigs lost weight and developed rachitic lesions in ribs and long bones. Generally the younger animals devel oped more bone abnormalities than the older animals. The teeth of all animals developed extreme enamel hypoplasia. As there were no control animals in this study, interpretation of these data is difficult.

Prevention of soft tissue calcification caused by imbalances among dietary calcium, phosphorus, potassium, and magnesium is of more concern in the formulation of practical diets for guinea pigs than the prevention of overt deficiencies. Hogan and Regan (1946) implicated excess phosphorus as a cause of soft tissue calcification in guinea pigs. These findings were confirmed when 90 percent of the guinea pigs fed a diet containing 8 g Ca/kg and 9 g P/kg developed soft tissue mineral deposits, whereas the incidence was less than 10 percent when the diet contained only 5 g P/kg (Hogan et al., 1950). In subsequent experiments, supplemental magnesium and potassium prevented the effects of excess dietary phosphorus, including soft tissue calcification, in guinea pigs (House and Hogan, 1955). These observations seem to be consistent with those for rats (see Chapter 2, Nephrocalcinosis in Rats Fed Purified Diets.)

Chloride, Sodium, and Sulfur

No published data could be found on the requirements of chloride, sodium, or sulfur for the guinea pig. The concentrations of chloride and sodium in purified diets used for rats should be used as a first approximation of the dietary concentrations of these nutrients.

Magnesium

The magnesium requirement of guinea pigs depends on the dietary concentrations of calcium, phosphorus, and potassium. Morris and O'Dell (1963) concluded that an excess of calcium or phosphorus independently increased the minimum magnesium requirement and that the effects were additive. As dietary phosphorus increased from 8 g to 17 g/kg diet, the minimum requirement for magnesium increased from 1 g to 4 g/kg diet. Similarly, as dietary calcium increased from 9 g to 25 g/kg diet, the requirement for magnesium increased.

Interactions of magnesium with potassium and fluoride are also important. Magnesium-deficient guinea pigs not only have reduced muscle extracellular and intracellular magnesium concentration (20 percent and 80 percent of control values, respectively) but also have reduced muscle potassium and increased intracellular sodium and water concentrations (Grace and O'Dell, 1970a). Supplementing the diets of magnesium-deficient guinea pigs with potassium stimulated growth, lowered blood phosphorus concentrations, decreased calcium concentrations in muscle, extended survival times, and decreased mortality. Guinea pigs appeared to use cations rather than ammonia to neutralize and excrete acid in the urine (O'Dell et al., 1956).

Adding 0.1 to 0.4 g fluorine/kg diet to a magnesium-deficient diet (0.4 g/kg diet) significantly improved growth, increased serum magnesium concentrations, reduced incidence of soft tissue calcification, and reduced calcium concentrations in kidney, heart, and liver (Pyke et al., 1967). When magnesium was severely limiting (0.1 g/kg diet), 0.2 g fluorine/kg diet was toxic and caused lameness and swollen feet; but adequate magnesium largely overcame the deleterious effects of excess fluorine in weanling guinea pigs (O'Dell et al., 1973).

On the basis of no new research, the magnesium requirement is 1 to 3 g/kg diet, 1 g/kg diet being the minimum requirement. However, if additional work were to demonstrate that current estimates of the requirements for calcium and phosphorus are high, the magnesium requirements would also need to be reevaluated.

Signs of Magnesium Deficiency Clinical signs of magnesium deficiency in young guinea pigs include poor growth, hair loss, decreased activity, poor muscular coordination and stiffness of hind limbs, elevated serum phosphorus, and anemia (Maynard et al., 1958; O'Dell et al., 1960; Morris and O'Dell, 1963). Convulsions, which characterize magnesium deficiency in some species, are uncommon in guinea pigs (O'Dell et al., 1960; Grace and O'Dell, 1970a), but one study reported tetany (Thompson et al., 1964). Gross tissue changes at necropsy were enlarged pale kidneys, white foci and streaks in liver, soft tissue calcification, and incisors that were darkened, eroded, and soft (Maynard et al., 1958; O'Dell et al., 1960; Morris and O'Dell, 1961). In addition, Grace and O'Dell (1970b) concluded that magnesium deficiency probably affected appetite and/or membrane transport of nutrients.

Potassium

The potassium requirements of guinea pigs depend on the dietary concentrations of calcium and phosphorus. Mortality was 100 percent within 4 weeks when young guinea pigs were fed a purified diet (30 percent casein) that supplied excess cations but only 1 g K/kg diet. The requirement for maximal growth under these circumstances was 4 to 5 g K/kg diet supplied as potassium acetate (Grace and O'Dell, 1968). Additional dietary potassium, up to 14 g K/kg diet, has been found to be required when diets combined very high concentrations of calcium, phosphorus, and magnesium (O'Dell et al., 1956; Morris and O'Dell, 1963). With moderate dietary concentrations of calcium, phosphorus, and magnesium, the requirement for potassium is 5 g/kg diet and should be considered generous.

Signs of Potassium Deficiency Luderitz et al. (1971) found that membrane potentials in striated muscle cells from young guinea pigs fed a potassium-deficient diet were higher than in control animals. These effects were accompanied by a significant, and apparently quantitative, increase in Na⁺, K⁺-ATPase activity in heart muscle cells (Erdmann et al., 1971).

Copper and Iron

Diets containing 6 mg Cu/kg diet have been reported to be adequate for normal growth and development of the guinea pig (Everson et al., 1967, 1968). If guinea pigs are fed diets containing less than 1 mg Cu/kg during pregnancy and early postnatal development, the offspring are characterized by growth retardation, cardiovascular defects, and severe abnormalities of the central nervous system including agenesis of cerebellar folia, cerebral edema, and delayed myelination (Everson et al., 1968). The dietary requirement for copper is increased if there are high concentrations of molybdenum (Suttle, 1974). Offspring of dams given 0.18 percent CuSO4 in their drinking water from day 21 of gestation on were characterized by high liver copper concentrations and subtle evidence of liver pathology (Chesta et al., 1989).

Dietary iron requirements of the guinea pig have not been directly addressed. Based on an evaluation of previous and current diets used for guinea pigs, it is estimated that a diet containing 50 mg Fe/kg will satisfy the iron requirements for reproduction, growth, and development. Dietary iron at high concentrations (200 to 300 mg/kg) can result in significant tissue iron concentration, although overt tissue pathology has not been reported (Smith and Bidlack, 1980; Caulfield and Rivers, 1990).

Manganese

A dietary concentration of 40 mg Mn/kg diet has been shown to be adequate for normal growth and development of the guinea pig (Everson et al., 1959). Similar to the mouse and rat (Hurley and Keen, 1987), diets containing 3 mg Mn/kg or less are inadequate for the guinea pig during growth and development. Although the manganese dietary requirement for the guinea pig is probably less than 40 mg/kg, in the absence of studies evaluating dietary manganese concentrations between 3 and 40 mg/kg diet, the recommended concentration is 40 mg/kg diet for all stages of life.

Signs of Manganese Deficiency In a series of studies by Everson (Tsai and Everson, 1967; Everson, 1968; Everson and Shrader, 1968; Everson et al., 1968; Shrader and Everson, 1968) it was established that signs of prenatal and early postnatal manganese deficiency include reduced litter size, abortions or stillbirths, congenital ataxia, skeletal abnormalities, and pancreatic pathology that resulted in a diabetes-like syndrome. The pancreatic pathology and diabetic syndrome can be reversed with manganese supplementation; the ataxia, however, is irreversible (Everson and Shrader, 1968; Shrader and Everson, 1968).

Zinc

Alberts et al. (1977) reported that casein-based diets containing 12 mg Zn/kg and soybean protein-based diets containing 20 mg Zn/kg were adequate to support optimal growth rate without evidence of deficiency signs in the young guinea pig. These values are consistent with the report by Navia and Lopez (1973) that purified gel diets containing 19 mg Zn/kg diet support normal growth and development. The requirement for zinc is 20 mg/kg diet for all stages of life.

Signs of Zinc Deficiency Guinea pigs fed diets containing less than 1.25 mg Zn/kg are characterized by low plasma zinc concentration, depressed ability to elicit a delayed-type hypersensitivity, low gamma-globulin concentrations, altered glycosaminoglycan metabolism, abnormal posture, skin lesions, anorexia, and excessive vocalization (McBean et al., 1972; Hsieh and Navia, 1980; Quarterman and Humphries, 1983; Gupta et al., 1988; Verma et al., 1988; O'Dell et al., 1989). If a zinc-deficient diet (≤2 mg Zn/kg) is given during pregnancy, it can result in premature delivery or abortion (Apgar and Everett, 1991b).

Iodine, Molybdenum, and Selenium

Diets unsupplemented with iodine, selenium, or molybdenum have been shown conclusively to have negative effects on the physiological or biochemical status of mammals. No systematic effort has been made to establish the requirements of iodine, molybdenum, and selenium for the guinea pig. Most of the research to establish requirements has been done with the laboratory rat. (For an indepth discussion, see Chapter 2.)

The dietary requirement for selenium of the rat and mouse has been determined by using the maximization of liver glutathione peroxidase activity (GSH-Px). This procedure may prove difficult in the guinea pig because the activity of this enzyme in the liver of the guinea pig is less than 10 percent of that in other species such as hamsters, rats, and mice. Apparently this phenomenon is not related to the amount of dietary selenium. Even if guinea pigs are fed commercial natural-ingredient diets containing more selenium (140 to 200 µg/kg) than the amount required by rats, GSH-Px activities in various tissues are very low.

Lawrence and Burk (1978) found no GSH-Px activity in livers of guinea pigs fed natural-ingredient diets, while Toyoda et al. (1989) found that liver, kidney, and heart had only 4 to 6 percent of the activity normally observed in similar tissues of mice or rats. In spite of low liver GSH-Px activity, excellent reproductive performance has been observed for many years in experimental and commercial guinea pig colonies fed commercially available natural-ingredient diets containing 140 to 330 µg Se/kg (Boyd O'Dell, University of Missouri, Columbia, MO, and Dennis Renner, Sasco Inc., Lincoln, NE, 1993, personal communications). These diets are reported to contain 400 to 1,000 µg I/kg but no added molybdenum. Although liver GSH-Px activity is lower in tissues of guinea pigs than in those of other species, liver selenium concentrations are comparable (Toyoda et al., 1989).

Although no work has been done to directly establish the iodine, molybdenum, or selenium requirements for the guinea pig, some evidence indicates that these requirements might be similar to those of rats and mice. Therefore, until more research is conducted, concentrations established for the rat can be used as a first estimate for requirement in the guinea pig. By no means, however, should this be construed to indicate that guinea pigs metabolize these elements exactly as do rats. The requirement for iodine at all stages of life is 150 µg/kg diet and that for molybdenum is 150 µg/kg diet. The requirement for selenium, as selenite, for all stages of life is 150 µg/kg diet with the exception of pregnancy and lactation, for which a dietary concentration of 400 µg Se/kg diet is suggested.

Vitamin A

Guinea pigs apparently have a high vitamin A requirement. Bentley and Morgan (1945) reported that 21 µmol vitamin A/kg diet maintained growth and a very modest store of vitamin A in the liver. Gil et al. (1968) found that 11.5 µmol/kg diet would maintain growth, but that normal tissue histology, and storage of vitamin A in the liver were only found with diets containing 23 µmol/kg diet or more. Intermediate concentrations were not tested. Although they did not measure liver vitamin A reserves, Howell et al. (1967) found that a dose of vitamin A equivalent to 18 µmol/kg diet was adequate to maintain vision, reproduction, and growth for 460 days. Reid and Briggs (1953) found that 18 µmol/kg diet was satisfactory for optimal growth in guinea pigs fed a purified diet.

β-Carotene is used by the guinea pig as a source of vitamin A (Chevallier and Choron, 1935, 1936; Woytkiw and Esselbaugh, 1951); however, the molar efficiency of utilization may be only 40 percent that of preformed vitamin A (Bentley and Morgan, 1945) when consumed at amounts near the requirement. The reason for this low efficiency of utilization has not been identified. In rats, an intake at this concentration would have a similar efficiency. The lower efficiency of β-carotene utilization at higher intakes is mainly caused by poor absorption from the intestine. β-Carotene is a pure hydrocarbon that is very difficult to solubilize at the higher concentrations.

Diets that contain 21,960 IU retinol/kg diet (23 µmol or 6.6 mg/kg diet) appear to maintain optimal health and a slightly positive vitamin A balance in guinea pigs. If β-carotene is used as the source of vitamin A activity, then 47,425 IU β-carotene/kg diet (53 µmol or 28 mg/kg) would be needed to maintain a slightly positive vitamin A balance.

Signs of Vitamin A Deficiency Time before onset of deficiency signs varies widely with age, liver vitamin A concentrations, and stress conditions. Young guinea pigs may develop deficiency signs in 2 weeks, whereas older pigs may require nearly 10 weeks when fed a diet devoid of vitamin A or provitamin A. The first evidence of vitamin A deficiency is poor growth, then weight loss, followed by incrustations of eyelids and severe dermatitis resulting from bacterial infection (Bentley and Morgan, 1945). Gross pathology studies often reveal accumulation of organic debris in the bile ducts and gallbladder, clouding of the cornea, and xerophthalmia. Often animals develop pneumonia prior to death. Histologically, epithelia of various organs showed squamous metaplasia and some keratinization (Howell et al., 1967).

The primary effect of a vitamin A deficiency on the incisors of guinea pigs is mainly on odontogenic epithelium with incomplete differentiation of cells, loss of organization, and formation of defective dentin by atrophic odontoblast (Wolbach, 1954). The incisors had a distinctive appearance characterized by thickened dentin on the labial side and thin dentin on the lingual and lateral sides.

Signs of Vitamin A Toxicity Excessive amounts of vitamin A given to guinea pigs caused degenerative changes in the cartilaginous epiphyseal plates of long bones (Wolbach, 1947), and there was increased bone resorption interfering with normal remodeling. Gil et al. (1968) reported "loss of weight" in guinea pigs fed diets containing 121 mg/kg diet (230 µmol/kg) or more of retinyl palmitate. Teratogenic effects were noted by Robens (1970) when a single oral dose (210 µmol/kg BW) given to pregnant guinea pigs during fetal organogenesis (days 14 to 20) caused soft tissue and skeletal anomalies in the offspring. The most frequent defects recorded were agnathia, synotia, malpositioning of teeth, and microstomia. Administration of the same dose between days 17 and 20 frequently produced changes in the tibias and fibulas, but fetal growth was not affected.

Vitamin D

A quantitative requirement for vitamin D has not been established for guinea pigs, but currently used natural-ingredient and purified diets contain between 20 and 180 nmol/kg diet (Reid and Briggs, 1953; Navia and Lopez, 1973; O'Dell et al., 1989). These amounts seem to promote growth at rates that were average for the colony. The requirement for growth is set at 1,000 IU vitamin D/kg diet (65 nmol/kg diet; 0.025 mg/kg diet).

Signs of Vitamin D Deficiency Guinea pigs fed diets with a normal calcium-to-phosphorus ratio do not develop gross signs of vitamin D deficiency (Kodicek and Murray, 1943). However, Sergeev et al. (1990) observed many changes in vitamin D status of guinea pigs fed a vitamin D-deficient diet containing 6 g calcium/kg diet and 6 g phosphorus/kg diet. Serum calcium and phosphorus concentrations were reduced, serum alkaline phosphatase was increased, serum 25-hydroxycholecalciferol concentrations were extremely low, kidney 1-α-hydroxylase activity was more than twice the normal concentrations, active transport of calcium in the duodenum was decreased, and bone calcium content was about four-fifths the control concentrations. Administering 5.2 nmol (15 IU) of cholecalciferol per animal every other day prevented the development of these signs. This is about twice the amount available from typical diets. Lower amounts were not used. A deficiency of ascorbic acid also altered the animal's ability to metabolize vitamin D. Howe et al. (1940) housed guinea pigs in a darkened room and fed them a low-vitamin D purified diet with 0.28 g Ca/kg and 2 g P/kg. In addition to retarded growth, typical lesions occurred in the zone of cartilage proliferation at the epiphyseal plate of long bones and ribs. Also, incisors exhibited a high degree of enamel hypoplasia, and enamel and dentin were disorganized and irregular with poor calcification.

Signs of Vitamin D Toxicity Guinea pigs show a response to excessive vitamin D intake. An extract of the poisonous plant Solanum malacoxylon caused hypercalcemia and calcification of kidney, aorta, muscles, spleen, heart, and liver (Camberos et al., 1970). This plant has been shown to contain derivatives of the active metabolites of vitamin D, which are responsible for the toxicity (Boland et al., 1987).

Vitamin E

No precise quantitative requirement for vitamin E can be given, in spite of studies with guinea pigs involving vitamin E and related nutrients. The earliest estimate of a minimum requirement for the growing guinea pig, eating a vitamin E-deficient diet containing 20 g cod liver oil/kg, is equivalent to 2.6 µmol RRR-α-tocopherol/day (Shimotori et al., 1940). Assuming a feed intake of 20 g/day, this is equivalent to 128 µmol/kg diet (82 IU or 55 mg RRR-α-tocopherol/kg diet. (See Chapter 2 for a discussion of the forms and potency of vitamin E.) Farmer et al. (1950) reported that 5.1 µmol/day was required for normal reproduction in the female guinea pig receiving cod liver oil. Assuming a feed intake of 30 g/day, this is equivalent to 170 µmol/kg diet (74 mg/kg). Several popular diets have been developed for the guinea pig that do not contain cod liver oil. Reid and Briggs (1953) originally developed their diet to contain a vitamin E activity equivalent to 34 µmol RRR-α-tocopherol/kg diet, but later Reid (1963) modified the diet to contain 82 µmol/kg diet. The diet described by Hsieh and Navia (1980) contained a vitamin E activity equivalent to 62 µmol RRR-α-tocopherol per kg diet. Based on the above, a diet containing 40 IU/kg diet (62 µmol or 26.7 mg/kg diet) should meet the needs of growing guinea pigs. There have been no reports of vitamin E deficiency with these diets.

Signs of Vitamin E Deficiency Diet-induced muscular dystrophy was produced in the guinea pig when 5 to 20 g cod-liver oil/kg was included in the diet. The research of Shimotori et al. (1940) related vitamin E deficiency to muscular dystrophy. An average oral dose of 1.5 mg of synthetic α-tocopherol per day provided protection against sign of muscular dystrophy during a 200-day period. Pappenheimer and Goettsch (1941) confirmed the role of vitamin E for maintenance of normal muscle and extended the observations to show the need for vitamin E during pregnancy. Schottelius et al. (1959) reported that vitamin E deficiency in guinea pigs precipitated a decrease in muscle myoglobin concentration. Reduced myoglobin concentration was observed before the appearance of severe tissue lesions or increased creatine excretion. Supplementation with vitamin E reduced the magnitude of the myoglobin change. Elmadfa and Feldheim (1971) have shown that creatine phosphokinase activity in skeletal muscle of young male guinea pigs was reduced significantly by feeding them a vitamin E-deficient diet for 2 weeks. The serum creatine phosphokinase activity increased during the same period. At about 4 weeks, creatine excretion in the urine increased, and by 6 weeks erythrocyte hemolysis increased, reaching a maximum at 8 weeks. Soon thereafter, the guinea pigs became prostrate with severe body weight loss and degeneration of skeletal muscle. In males, testes atrophied and developed degenerative changes in the seminiferous tubules, with clumping or complete disappearance of spermatozoa and spermatids. Fetal malformations, resorption, and death occurred in pregnant females.

Vitamin K

The information to develop a specific recommendation for the vitamin K requirement of guinea pigs does not exist. The menadione content of some of the more frequently used diets ranges from 12 to 58 µmol/kg diet (Reid and Briggs, 1953; Navia and Lopez, 1973; O'Dell et al., 1989). These diets appear to be adequate to prevent hemorrhages, but no information is available about more sensitive indicators of vitamin K status. Based on limited information, a concentration of 5 mg phylloquinone/kg diet (11 µmol phylloquinone/kg diet) is suggested.

Signs of Vitamin K Deficiency The drug Warfarin prevents the normal recycling of vitamin K and thereby rapidly causes a nonfunctional form of vitamin K to accumulate in the tissues. In guinea pigs treated with Warfarin, prothrombin concentrations dropped to 14 percent of control concentrations within 24 hours (Carlisle et al., 1975); and a greatly reduced amount of γ-carboxyglutamic acid in plasma proteins was noted (Stenflo and Fernlund, 1984). Thus, Warfarin and vitamin K appear to interact in guinea pigs much the same as they do in rats.

Ascorbic Acid

The ascorbic acid requirement of the guinea pig has been reviewed by Mannering (1949). Navia and Hunt (1976) summarized the major metabolic roles for ascorbic acid in this animal. The daily requirement of ascorbic acid varied from 0.4 to 25 mg/day according to the criterion used to evaluate adequacy. Values reported to support growth were 0.4 to 2 mg/day in 250 to 350 g guinea pigs; reproduction was supported by 2 to 5 mg/day (Mannering, 1949). Scurvy was prevented by 1.3 to 2.5 mg/day; odontoblast growth, wound healing, and bone regeneration were supported by 2 mg/day; and tissue saturation occurred at 25 to 30 mg/day. Approximately 7 mg of ascorbic acid/kg BW was adequate to maintain adrenal size and odontoblast height in male guinea pigs ranging from 110 to 840 g BW (Pfander and Mitchell, 1952). Collins and Elvehjem (1958) found 5 mg/kg BW sufficient for growth of immature guinea pigs.

The liver, kidney, plasma, lens, and aqueous humor concentration of ascorbic acid reflected the amount of ascorbic acid fed (0.8 to 60 mg/animal/day) to both young and old guinea pigs. The half-life of tissue ascorbate was reported to be the same in guinea pigs provided a maintenance dose (0.5 mg/day) or a higher dose (30 mg/100 g BW/day) (Ginter et al., 1982). A concentration of 50 mg/kg diet was marginal for survival. At 200 mg/kg diet, hepatic ascorbic acid accumulated in the liver. Adrenal and splenic concentrations increased with concentrations of 900 mg/kg diet (Degkwitz and Boedeker, 1989). Higher tissue concentrations were achieved by mixing the vitamin in the diet (500 mg/kg) than by daily oral administration (Ginter et al., 1979). An intake of 5 mg/day provides adequate amounts of ascorbic acid for growth and reproduction; normal intake of 200 mg/kg diet (1,135 µmol/kg diet) will fulfill this need.

Ascorbic acid absorption was reported to be sodium dependent and involve a transporter molecule (Siliparandi et al., 1979). Dehydroascorbic acid was readily absorbed and reduced by dehydroascorbic acid reductase to ascorbic acid in the intestinal mucosa. Transport of endogenous ascorbate across the basolateral membrane assures the mucosal cell access to the vitamin in the absence of a dietary supply (Rose et al., 1988).

The stability of ascorbic acid in diets varies with the composition of the diet, storage temperature, and humidity. Approximately one-half of the initial ascorbic acid may be oxidized and lost 90 days after the diet has been mixed. Aqueous solutions may lose vitamin C potency rapidly.

Ascorbic acid at 0.5 mg/kg BW prevented rapid fatal scurvy and 55 percent of guinea pigs survived, but after 16 weeks these animals exhibited a marked increase in serum cholesterol, LDL-cholesterol, VLDL-cholesterol, triglycerides, and total lipids. The LDL:HDL ratio rose from 1.13 to 19.02 with cholesterol added at 3 g/kg diet (Kothari and Sharma, 1988) and stimulated the oxidation of ascorbic acid to carbon dioxide (Ginter and Zloch, 1972). Magnesium L-ascorbic acid phosphate has been shown to cure scurvy in the guinea pig (Machlin et al., 1979), but L-ascorbic acid 2-sulfate did not have antiscorbutic activity (Tsujimura, 1978).

Signs of Ascorbic Acid Deficiency Early signs of vitamin C deficiency in guinea pigs were reduced diet intake and weight loss, followed by anemia and widespread hemorrhages. An impaired clotting mechanism, as indicated by increased prothrombin time, also contributes to hemorrhaging with vitamin C deficiency. Resting body temperatures were higher in scorbutic guinea pigs than normal animals (Green et al., 1980). Deficiency resulted in muscle damage but not neuropathy (Sillevis Smitt et al., 1991). Ascorbic acid-deficient animals were dead within 3 to 4 weeks from the causes noted above or from secondary bacterial infections, to which guinea pigs are susceptible. Ascorbate deficiency has been linked to an impairment in carnitine synthesis, increased urinary carnitine excretion, and prolonged survival time with carnitine supplementation (Jones and Hughes, 1982; Alkonyi et al., 1990).

Vitamin C deficiency resulted in decreased vitamin B₁₂ absorption; increased absorption of alanine and leucine; enhanced activity of brush border sucrase, alkaline phosphatase, and leucine aminopeptidase; and higher concentrations of intestinal membrane sialic acid and total lipids (Dulloo et al., 1982). Deficiency also reduced oxalate absorption (Farooqui et al., 1983). Growth and maintenance of connective tissue in skin, fetal tissues, and repairing wounds required a supply of dietary ascorbic acid (Barnes et al., 1969a,b, 1970; Rivers et al., 1970). The characteristic hemorrhages in subcutaneous tissues, joints, skeletal muscle, and intestine of scorbutic guinea pigs result in defects in connective tissue. Ascorbic acid is essential in hydroxylase reactions for the formation of hydroxyproline and hydroxylysine in the collagen molecule (Stone and Meister, 1962; Udenfriend, 1966). General weight loss in scorbutic guinea pigs resulted in decreased proteoglycan and collagen synthesis (Chojkier et al., 1983; Spanheimer and Peterkofsky, 1985; Bird et al., 1986a,b). Impaired synthesis of collagen had many effects on the guinea pig, including enlarged costochondral junctions, disturbed epiphyseal growth centers of long bones, bone loss, altered dentin, and gingivitis. Deficiency in ascorbic acid reduced cytochrome P-450 more than 50 percent (Rikans et al., 1977). Urinary excretion of fluoride was greater in guinea pigs on low ascorbic acid and protein diets (Parker et al., 1979).

Vitamin C deficiency has been reported to result in elevated serum copper and ceruloplasmin and liver copper concentrations (Milne and Omaye, 1980). Ascorbate deficiency has been reported to reduce thymus size, lower the delayed type hypersensitivity response, and active and total rosette-forming cells against sheep red blood cells (Majumder and Rahim, 1987). During the progression of a deficiency, the percentage of B lymphocytes increased and T lymphocytes decreased (Fraser et al., 1980). Leukocyte chemotaxis was impaired in guinea pigs fed 0.5 mg/kg BW compared to 20 mg/kg BW (Johnston and Huang, 1991). Antibody response to an injected antigen occurred more rapidly and was more pronounced in deficiency (Prinz et al., 1980). Splenic cell cyclic GMP and erythrocyte ATPase were depressed by a deficiency of vitamin C (Barkagan and Gelashvili, 1970; Haddox et al., 1979).

Biotin

No quantitative requirement for biotin has been demonstrated for normal healthy guinea pigs. Reid (1954b) observed no significant change in growth of young guinea pigs fed a purified diet with biotin omitted. Feeding guinea pigs a biotin-deficient diet containing raw egg white produced weight loss, alopecia, and depigmentation of the hair (Coots et al., 1959). Based on limited information a concentration of 0.2 mg biotin/kg diet (0.82 µmol/kg diet) is suggested as the requirement for all stages of the life cycle.

Choline

The inclusion of 7.2 mmol choline as 1.8 g choline bitartrate/kg diet supported acceptable growth of young guinea pigs fed a diet containing 30 percent casein (Reid, 1955). Although methionine does seem to have some sparing effect on the choline requirement, methionine could not be used to replace choline.

Signs of Choline Deficiency Choline deficiency has been characterized in young guinea pigs (Reid, 1954b, 1955). When 2- to 4-week-old guinea pigs were fed a 30 percent casein diet lacking added choline, but adequate in folic acid and vitamin B₁₂ (23 and 0.03 µmol/kg diet, respectively), poor growth, anemia, and muscle weakness were observed. Some adrenal and subcutaneous hemorrhages occurred, but no renal hemorrhage or marked fatty infiltration of liver were reported.

Folates

The young guinea pig appears to have a high requirement for folic acid, on the order of 3 to 6 mg/kg diet (6.8 to 13.6 µmol/kg diet) (Mannering, 1949; Woodruff et al., 1953; Reid 1954a; Reid et al., 1956). Guinea pigs practice coprophagy and may obtain folic acid from bacterial synthesis in the gastrointestinal tract. As the animal matures, less folic acid is required.

Signs of Folate Deficiency Young guinea pigs fed a folic acid-deficient diet grew slowly initially and became weaker as diet intake declined. Anemia and leukopenia developed. Hemoglobin and hematocrit values decreased, and the bone marrow became aplastic. Fatty livers and adrenal hemorrhages were prominent at necropsy (Woodruff et al., 1953; Reid, 1954a; Reid et al., 1956).

Niacin

Guinea pigs require a dietary intake of niacin (Reid, 1954b). However, because they can produce niacin from tryptophan, the niacin requirement is influenced by quantity and quality of dietary protein, especially tryptophan content and availability. According to Reid (1961), 10 mg niacin/kg diet (81 µmol/kg diet) was adequate in a purified diet containing 30 percent casein or 20 percent casein supplemented with 1 percent L-arginine and 0.25 percent DL-methionine.

Signs of Niacin Deficiency The most definitive reports on niacin deficiency in the guinea pig are those of Reid (1954b, 1961). When niacin was omitted from a purified diet containing 30 percent casein, deficiency signs were observed in 3 to 4 weeks. All niacin-deficient animals exhib ited poor growth; small appetite; pale feet, nose, and ears; drooling; anemia; and a tendency to diarrhea. The animals also had lowered hemoglobin and hematocrit. No oral or ocular lesions and no dermatitis were observed.

Pantothenic Acid

Reid and Briggs (1954) reported that 20 mg or 42 µmol calcium pantothenate/kg diet was adequate for optimal growth. They did not indicate whether calcium d-pantothenate or calcium dl-pantothenate was used. The adult requirement has not been established. It is projected to be similar to that of young animals, as nonpregnant or pregnant adults can be depleted rather rapidly (Hurley et al., 1965).

Signs of Panthothenic Acid Deficiency Young guinea pigs fed a purified, pantothenic acid-deficient diet developed signs of deficiency such as decreased growth rate, anorexia, weight loss, rough coat, diarrhea, weakness, and death (Reid and Briggs, 1954). Hair pigmentation was unaffected, and the adrenals were enlarged and sometimes hyperemic or hemorrhagic. Adult animals fed a pantothenic acid-deficient diet died within 10 to 41 days (Hurley et al., 1965). Many of them had adrenal and gastrointestinal hemorrhages.

Pyridoxine

Based on weight gain and general appearance of the growing guinea pig, the quantitative requirement of pyridoxine is 2 to 3 mg/kg diet (9.7 to 14.6 µmol/kg diet) (Reid, 1964).

Signs of Pyridoxine Deficiency When fed a purified diet containing 30 percent casein with no pyridoxine added, 15 of 27 animals lived for 8 weeks (Reid, 1964). These animals grew slowly, but showed no specific signs of deficiency. Some pyridoxine may have been present in the casein used in the diet.

Riboflavin

The limited research by Slanetz (1943), Reid (1954b), and Hara (1960) is inadequate to establish a riboflavin requirement for the guinea pig. The best estimate is 3 mg riboflavin/kg diet (8 µmol riboflavin/kg diet) (Slanetz, 1943).

Signs of Riboflavin Deficiency By feeding young guinea pigs a purified diet deficient in riboflavin, Reid (1954b) found that they exhibited poor growth; rough hair; pale feet, nose and ears; and early death (2 weeks). Later, Hara (1960) described microscopic lesions, such as corneal vascularization, skin atrophy and chromatolysis, and myelin degeneration in the pons and spinal cord. Myocardial alterations included hemorrhage and edema accompanied by vacuolar degeneration and atrophy.

Thiamin

The thiamin requirement of the young guinea pig is 2 mg thiamin-HCl/kg diet (5.9 µmol/kg diet) (Liu et al., 1967; Reid and Bieri, 1967). No reports are available to support a definite quantitative requirement for gestation and lactation.

Signs of Thiamin Deficiency Young growing guinea pigs fed a thiamin-deficient diet exhibited reduced food intake and weight loss, followed by the development of central nervous system disorders. An unsteady gait and some retraction of the head also occurred as the condition progressed. Death occurred within 4 weeks (Liu et al., 1967; Reid, 1954b; Reid and Bieri, 1967).

Myo-Inositol

There is no evidence that the guinea pig requires a dietary source of inositol. Reid (1954b) did not observe significant growth retardation when inositol was omitted from a purified diet.

Vitamin B12

There is no evidence that the growing guinea pig requires a dietary source of vitamin B₁₂ (Reid, 1954b). Guinea pigs may ingest a significant amount of this vitamin during coprophagy.