Effect of parturition on levels of vitamins A and E and of beta-carotene in plasma and milk of mares.

The objective of this study was to investigate in mares the effect of parturition on plasma and milk levels of retinol, beta-carotene, alpha-tocopherol and cholesterol over 12 weeks around parturition. In blood plasma of horses around parturition an increase of all these components was observed. This increase was most impressive in beta-carotene (P<0.05) and less pronounced for vitamin E, vitamin A and cholesterol. The magnitude of increase around parturition corresponded well with the magnitude of accumulation in colostrum; levels of beta-carotene in colostrum were 65 times higher compared to mature milk while vitamin A, vitamin E and cholesterol were only 3 to 8 times higher. Beta-carotene concentrations in colostrum were positively correlated with corresponding plasma levels (r = 0.9; P<0.001). Reasons for the increase in plasma beta-carotene around parturition may include an improved absorption of carotene and/or reduced conversion into vitamin A as well as mobilisation from tissue storages or a reduced uptake in tissues other than the mammary gland. In conclusion, the results may point to possible component- and species-specific differences involved in the transfer of fat-soluble vitamins, beta-carotene and cholesterol from blood plasma into colostrum.