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Companion Animals: Vitamin A
Requirements

Practical factors influencing vitamin A requirements for various species are listed in Table 1. Minimum requirements, determined by various methods, include amounts required to prevent night blindness, amounts required for storage and reproduction, and amounts required for maintenance of normal pressure in the cerebrospinal fluid (CSF). The minimum vitamin A requirement for normal growth may be lower than that required for higher rates of gain, resistance to various diseases and normal bone development.
Table 1

Different species of animals convert beta-carotene to vitamin A with varying degrees of efficiency (Table 2 ). Some factors that influence the rate at which carotenoids are converted to vitamin A are type of carotenoid, class and production level of animal, individual genetic differences in animals and level of carotene intake. Efficiency of vitamin A conversion from beta-carotene is decreased with higher levels of intake (Van Vliet et al., 1996). The conversion rate of the rat has been used as the standard value, with 1 mg of beta-carotene equal to 1,667 IU of vitamin A. Dogs are only 50% as efficient, while the cat cannot utilize vitamin A precursors.
Table 2
A. Requirements for Dogs

Frohring (1935; 1937) fed vitamin A-deficient diets to puppies and determined that for growth 100 IU vitamin A per kg (45.5 IU per lb) body weight was lost from the liver daily. Crimm and Short (1937), using a similar vitamin A depletion technique, estimated that the minimal daily vitamin A requirement of adult dogs was 22 to 47 IU per kg (10 to 21.4 IU per lb) of body weight.

The NRC (1985) suggests that the daily vitamin A requirement would be met by 75 IU per kg (34.1 IU per lb) of body weight for adult maintenance and 202 IU per kg (91.8 IU per lb) of body weight for growing puppies. These amounts will be more than provided by a dietary concentration (dry basis) of 3,336 IU per kg (1,516.4 IU per lb). These estimated requirements are considerably lower than the NRC (1974) and the Association of American Feed Control Officials (AAFCO, 1992) recommendations, which suggest 5,000 IU of vitamin A per kg (2,272.7 IU per lb) of diet.
B. Requirements for Cats

The cat, compared to other species, has a high vitamin A requirement relative to its body size. Controlled studies designed to define the vitamin A requirements have not been published. However, the requirement has been estimated to range from 1,600 to 2,000 IU of preformed vitamin A per head per day (Scott, 1965; Gershoff et al., 1957a).

In long-term studies, 4,000 IU retinol per kg (1,818.2 IU per lb) of diet was not adequate for pregnancy, but 6,000 IU per kg (2,727 IU per lb) prevented deformities and provided for normal kitten development during lactation (NRC, 1985). AAFCO (1992) suggests a minimum of 7,500 IU per kg (3,409 IU per lb) of diet for all classes of cats.

 
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