Effects of RRR-α-tocopheryl acetate supplementation during the transition period on vitamin status in blood and milk of organic dairy cows during lactation

This study investigated effects of daily supplementation with RRR-α-tocopheryl acetate, during the transition period around calving, on concentrations of α-tocopherol in plasma and milk from prepartum to mid-late lactation of dairy cows. Retinol and β-carotene contents also were measured. The study included 2 experiments, where all cows were fed 100% organic diets, with high proportions of grass-legume forage. The experimental design was a randomised complete block. In experiment 1, the basal diet contained 70 and 60 IU of RRR-α-tocopherol/kg DM (dry period and lactation, respectively) and was supplemented with 0 (C) or 2400 (E) IU of RRR-α-tocopheryl acetate from 3 weeks before to 3 weeks post calving (PC). In experiment 2, the basal diet contained 29 IU of RRR-α-tocopherol/kg DM plus 31 (dry) or 20 (lactating) IU of synthetic vitamin E/kg DM and was supplemented with 0 (C) or 2400 (E) IU of RRR-α-tocopheryl acetate from 3 weeks before to 3 weeks PC. Synthetic vitamins A and D also were supplemented in experiment 2. Blood samples were collected at 3 weeks before expected calving, at calving, at 3 weeks PC and between 5 and 7 months PC, while milk samples were collected from colostrum, at 4 days PC, at 3 weeks PC and between 5 and 7 months PC. In both experiments, E cows tended to have higher plasma concentrations of α-tocopherol at calving than C cows. At 3 weeks PC, concentrations in plasma were 34% and 22% higher in E cows than in C cows in experiment 1 and 2, respectively (P < 0.05). The treatments resulted in similar vitamin concentrations in milk in experiment 1. In experiment 2, the basal diet was low in RRR-α-tocopherol, and E cows had 61%, 207% and 181% higher concentrations of α-tocopherol than C cows in the milk from colostrum, 4 days PC and 3 weeks PC, respectively (P < 0.05). There were no differences between treatments in either plasma or milk later in lactation. High concentrations of α-tocopherol and β-carotene in forage decreased the effect of the E treatment. However, as concentrations of α-tocopherol and β-carotene in forage are difficult to predict vitamin supplementation is recommended, especially around calving. Retinol concentrations in plasma in experiment 1 were generally low (< 0.25 mg/l during the transition period), indicating that vitamin A supplementation also is necessary, especially during the transition period.