Relative bioavailability of vitamin E in dairy cows following intraruminal administration of three different preparations of DL-alpha-tocopheryl acetate

DL-α-tocopheryl acetate, a synthetic form of vitamin E, is routinely given as a dietary supplement to cattle. In this study we assessed the relative bioavailability of three formulations of DL-α-tocopheryl acetate in a kinetic study of plasma α-tocopherol in four Italian Friesian dairy cows, following intraruminal administration of a gelatin capsule containing 5 000 IU of DL-α-tocopheryl acetate. A Latin square design was used so that each animal received all formulations: (A) adsorbed on silica, (M) microencapsulated and (O) in oil form; 5 000 IU of DL-α-tocopheryl acetate was also administered intraperitoneally. The treatments were given following a 2-week period on a diet having no vitamin E supplementation with an interval of 8 days between each administration. Blood samples were collected at 0, 1, 10, 11, 21, 30, 48, 72, 96 and 168 h after each administration. The mean initial plasma α-tocopherol concentration (C(O)) was 2.38 ± 0.57 μg/mL. Maximum plasma concentrations (C(max)) of α-tocopherol, adjusted for pretreatment values, were 3.90 ± 0.13, 3.29 ± 0.13 and 4.07 ± 0.19 μg/mL, following administration of the A, M and O forms, respectively. The length of time required to obtain the maximum concentration (T(max)) in plasma was 57.5 ± 7.8, 76.8 ± 8.9 and 73.1 ± 14.1 h, and the area under the curve (AUC) was 503.3 ± 63, 620.25 ± 108.5 and 465.4 ± 38.7 μg.h/mL for A, M and O forms, respectively. Administration significantly increased the plasma α- tocopherol levels in all cases; however the A and M formulations had a lower elimination rate than the O form.