Alpha-tocopherol, selenium and polyunsatured fatty acid concentrations in the serum and feed of spring-calving dairy heifers

24 Friesian heifers were fed winter diets consisting either of hay with or without selenium supplementation, or pasture and silage with or without selenium supplementation. Heifers fed hay diet (α-tocopherol concentration 19 mg/kg of dry matter) resulted in a pre-calving serum α-tocopherol concentration of 1.2 mg/litre (deficient) compared with 4.5 mg/litre for pastured heifers. Serum fatty acid concentration, and the proportion of polyunsaturated fatty acids were lowest in the hay-fed heifers before calving (1.0 mg/ml and 37.1% respectively), and remained unchanged following re-introduction to pasture after calving in late July and August. In October, however, the proportion of polyunsaturated fatty acids in serum increased (50%), as did serum α-tocopherol concentrations (greater than 13 mg/litre). Mean serum selenium concentrations in the unsupplemented heifers ranged from 139 to 204 nmol/litre, being lowest in October. Supplementation with intraruminal selenium pellets (3 mg of selenium/day) increased serum selenium concentration and glutathione peroxidase activity whereas the type of diet had no effect. These results suggested that dairy cattle wintered on hay can become vitamin E-depleted, whereas the feeding of pasture and silage should provide adequate vitamin E. The pasture offered following calving during July and August provided a low dietary polyunsaturated fatty acid challenge, suggesting that abnormal peroxide metabolism is unlikely to be an important mechanism in the impaired performance of selenium-deficient adult cattle which calve at this time of year.