There is still a lack of experimental information on the level of vitamins
required in well-balanced horse diets, as well as on which vitamins need to be
added (Cunha, 1991). The vitamins most likely deficient for all classes of
horses are vitamins A and E, with vitamin D also deficient for horses in
confinement. Vitamin D may need to be received by race horses that are
exercised only briefly in the early morning, when sunlight provides little
antirachitic protection. Requirements for vitamins A, D and E can be met with
a high quality (e.g., green color) sun-cured hay. Deficiencies of vitamin K
and the B vitamins appear to be less likely in the mature horse than in other
monogastric species because many vitamins are synthesized in the cecum of the
horse. It is not known, however, to what extent the vitamins synthesized in
the cecum are absorbed. Since it is difficult to assess the intestinal
synthesis, many horse owners use B vitamin supplementation in diets for the
young horse and those being developed for racing or performance purposes
(Cunha, 1991).
In recent years, vitamin supplementation has become more critical to the horse
as the trend toward total confinement has increased. Presently, fewer horses
receive a high level of vitamin intake from a lush, green pasture or from a
high quality, leafy green hay. Cunha (1991) suggested that a vitamin premix
for horses contain vitamins A, D, E, K, thiamin, riboflavin, niacin, B6,
pantothenic acid, biotin, folic acid, B12 and choline. Biotin supplementation
is recommended, as Comben et al. (1984) showed a benefit of the vitamin for
hoof integrity. Recently there is a suggestion that carnitine supplementation
is beneficial for horses. Vitamin E may have an effect on the susceptibility
of horses to exercise-induced muscle damage (Bequin and Genetzky, 1985).
Dietary levels of vitamin E greater than 80 IU per kg and potentially 300 IU
per kg are required to maintain the blood and muscle vitamin E concentrations
in horses undergoing exercise conditioning.
The need for vitamins by horses, as well as other companion animals, would be
different than for food producing animals. For companion animals soundness and
longevity are important considerations. Food producing animals are slaughtered
at a younger age and generally would not be affected by cancer, kidney failure
and heart disease as would older animals. For older animals, particularly
those experiencing stress (e.g., confinement), more concern is needed for
supplying the antioxidant vitamins (e.g., vitamin E, vitamin C and
beta-carotene).
