Vitamin A, E and D nutrition in mares and foals during the winter season: effect of feeding two different vitamin-mineral concentrates.

The effects of feeding two different vitamin-mineral concentrates on serum levels of vitamins A, E and D and some growth indicators were examined in 30 pregnant mares and 30 foals. One concentrate contained vitamins A and E and the other did not. Both contained vitamin D3. No differences (P greater than .05) in serum levels of retinol and alpha-tocopherol were observed between the feeding groups in the mares, whereas in the weanlings serum levels of dietary vitamins A and E increased (P less than .01) during late winter and early spring. However, the values did not increase to levels found in summer. Serum 25-hydroxyvitamin D levels were very low (compared with animals of other species) in October, decreased (P less than .05) in winter and increased somewhat during the spring. The decrease in January was more pronounced in horses receiving vitamin concentrates containing less vitamin D. These results are interpreted to indicate that, in Finland, the commonly used amounts of dietary vitamins A and E or their bioavailability in vitamin-mineral concentrates are not sufficient to maintain serum concentrations in winter even close to the levels found in horses on pasture. Vitamin D status of horses is difficult to study due to very low serum levels of 25-hydroxyvitamin D.