Response of cows consuming adequate selenium to vitamin E and selenium supplementation prepartum

A 2-yr study of 195 parturitions was to evaluate the prepartum need for supplemental vitamin E and selenium by cows consuming diets that contained ample amounts of selenium (.1 to 2.0 ppm selenium). One-half of the cows were injected with 68 IU vitamin E and 5 mg selenium per 45.4 kg body weight approximately 21 days prepartum. Incidences of retained placenta and calving difficulty were similar for treated and control cows. There was a lower incidence of retained placenta (7.5%) for cows that calved during fall, whereas incidence was greater than 20% in cows that calved during the rest of the year. Serum vitamin E and selenium concentrations in treated cows doubled within a day after injection, then declined to concentrations typical of untreated cows within 8 and 3 days postinjection, respectively. Serum carotene, vitamin A, and vitamin E concentrations were similar for treated and control cows and were elevated in cows that calved during the summer and fall, possibly because cows dry during the grazing season were pastured. However, discriminant analysis of 21-day prepartum serum data indicated that serum concentrations of carotene, vitamins A or E, or selenium would not predict accurately the retention of the placenta. Colostrum and 4-day milk from treated and control cows contained similar amounts of vitamin E and selenium.