Vitamins:
Fat-soluble vitamins:
Forage and sunlight can provide a significant amount of the daily needs of the fat-soluble vitamins but hay-fed animals can develop deficiencies. Hay stored for 2 years was shown to have only 10% of the carotene (precursor to vitamin A) concentrations of fresh hay. Hay cut and rained on and then baled may have already lost much of the carotene content (NRC, 1989, p. 19)
Vitamin A:
Horses do not convert dietary beta carotene to vitamin A efficiently. This process takes place in the small intestine and horses on forage have much higher concentrations of vitamin A in serum than those on hay or even supplemented with vitamin A (NRC, 1989, p. 20).
Deficiency symptoms include night blindness, hyperkeratinization (excess keratin protein) of skin and cornea, poor growth, respiratory infections, salivary gland abscesses, poor conception, convulsive seizures and high cerebrospinal fluid pressure and weakness (NRC, 1989, p. 21).
Excesses may cause fragile bones, rough coats, poor muscle tone, depression and unthriftyness (NRC, 1989, p. 21)
Vitamin D:
Like other mammals, vitamin D is necessary for proper calcium and phosphorus absorption and utilization in the horse. Unlike ruminants and some other mammals, vitamin D deficiency (rickets) does not seem to be a problem. Toxicity can occur however at higher amounts of vitamin D (NRC, 1989, pp. 21-22).
Vitamin E:
Vitamin E is actually at least 8 compounds found in nature, alpha tocopherol appears to be the most biologically active for the horse (NRC, 1989, p. 22).
Vitamin E is needed with selenium in the body, both act as antioxidants, important in detoxification and cell defense (NRC, 1989, p. 23)
In order to be stable and not oxidize in a formula, vitamin E is esterified, the bond of which is broken during digestion, at which point vitamin E becomes an antioxidant again (NRC, 1989, p. 23).
Endurance is linked to vitamin E, muscles without adequate vitamin E show stress and damage during prolonged exercise (NRC, 1989, p. 23).
Vitamin E is also linked to immune function and horses with adequate vitamin E and selenium had improved immune function (NRC, 1989, p. 24)
Differentiating between vitamin E needs and selenium needs is difficult, horses with a lack of one or the other or both showed muscle ataxia and degeneration of neural processes and nervous system degradation (NRC, 1989, p. 24)
Water-Soluble Vitamins:
Forage provides all the B vitamins except B 12 (with is synthesized in the cecum and colon from dietary cobalt) and the adult horse can synthesize and absorb the B vitamins in the intestinal tract (NRC, 1989, p. 25).
References:
National Research Council. 1989. Nutrient Requirements of Horses, 5th Ed. Wash. DC: Natl Academy Press.
Fat-soluble vitamins:
Forage and sunlight can provide a significant amount of the daily needs of the fat-soluble vitamins but hay-fed animals can develop deficiencies. Hay stored for 2 years was shown to have only 10% of the carotene (precursor to vitamin A) concentrations of fresh hay. Hay cut and rained on and then baled may have already lost much of the carotene content (NRC, 1989, p. 19)
Vitamin A:
Horses do not convert dietary beta carotene to vitamin A efficiently. This process takes place in the small intestine and horses on forage have much higher concentrations of vitamin A in serum than those on hay or even supplemented with vitamin A (NRC, 1989, p. 20).
Deficiency symptoms include night blindness, hyperkeratinization (excess keratin protein) of skin and cornea, poor growth, respiratory infections, salivary gland abscesses, poor conception, convulsive seizures and high cerebrospinal fluid pressure and weakness (NRC, 1989, p. 21).
Excesses may cause fragile bones, rough coats, poor muscle tone, depression and unthriftyness (NRC, 1989, p. 21)
Vitamin D:
Like other mammals, vitamin D is necessary for proper calcium and phosphorus absorption and utilization in the horse. Unlike ruminants and some other mammals, vitamin D deficiency (rickets) does not seem to be a problem. Toxicity can occur however at higher amounts of vitamin D (NRC, 1989, pp. 21-22).
Vitamin E:
Vitamin E is actually at least 8 compounds found in nature, alpha tocopherol appears to be the most biologically active for the horse (NRC, 1989, p. 22).
Vitamin E is needed with selenium in the body, both act as antioxidants, important in detoxification and cell defense (NRC, 1989, p. 23)
In order to be stable and not oxidize in a formula, vitamin E is esterified, the bond of which is broken during digestion, at which point vitamin E becomes an antioxidant again (NRC, 1989, p. 23).
Endurance is linked to vitamin E, muscles without adequate vitamin E show stress and damage during prolonged exercise (NRC, 1989, p. 23).
Vitamin E is also linked to immune function and horses with adequate vitamin E and selenium had improved immune function (NRC, 1989, p. 24)
Differentiating between vitamin E needs and selenium needs is difficult, horses with a lack of one or the other or both showed muscle ataxia and degeneration of neural processes and nervous system degradation (NRC, 1989, p. 24)
Water-Soluble Vitamins:
Forage provides all the B vitamins except B 12 (with is synthesized in the cecum and colon from dietary cobalt) and the adult horse can synthesize and absorb the B vitamins in the intestinal tract (NRC, 1989, p. 25).
References:
National Research Council. 1989. Nutrient Requirements of Horses, 5th Ed. Wash. DC: Natl Academy Press.
By Alethea Kenney, copyright 2021-2025. Do not copy or reprint without permission.