α-tocopherol and β-carotene in forages and their utilisation by dairy cows in organic production

There are large variations in α-tocopherol (vitamin E) and β-carotene (pro-vitamin A) concentrations in forages. α-Tocopherol and β-carotene are antioxidants and important for the health and fertility of cows. This thesis investigated the effects of site, year, forage species, cutting date, wilting and ensiling technique on α-tocopherol and β-carotene concentrations in forage. Utilisation of vitamins E and A in dairy cows was also studied. Different grass-legume mixtures of the forage species birdsfoot trefoil, red clover, timothy and meadow fescue were sown at two sites in Sweden; Skara in the south and Umeå in the north. The mixtures were harvested at three occasions in the spring growth. At an additional site in Denmark, perennial ryegrass was used instead of meadow fescue. White clover was also included in Denmark and forages were harvested in a four-cut system. Vitamin analysis was performed on forage species from all mixtures and cutting dates. Silages treated with acid or bacterial inoculant were compared to untreated silages from a regrowth of forage mixtures in Skara. Dairy cows were offered a high daily dose of esterified natural vitamin E during the transition period (E) and were compared to cows without supplementation (C). Concentrations of α-tocopherol, β-carotene and retinol were measured in the blood and milk during lactation. Forages grown at Skara generally had higher vitamin concentrations than forages grown at Umeå. Differences between years were smaller. Birdsfoot trefoil generally had higher vitamin concentrations than red clover, whereas differences between grasses were more inconsistent. Cutting date had less effect at Umeå than Skara, irrespective of leaf blade proportion and developmental stage. In Denmark, numerical differences indicate that vitamin concentrations were higher in the fourth harvest than in earlier harvests, which was possibly a seasonal effect. The α-tocopherol concentration in the mixture with birdsfoot trefoil increased during ensiling and was higher in silages with birdsfoot trefoil than in silages with red clover. Inoculant-treated silage with red clover had higher α-tocopherol content than untreated silage with red clover. The E cows had higher concentrations of α-tocopherol in the blood than the C cows, when the supplement was offered. No effects of treatment on vitamin concentrations in blood were found later in the lactation. Treatment effects on vitamin concentrations in milk were affected by the vitamin concentration of the forage.