Long-term fluctuations and effect of age on serum concentrations of certain fat-soluble vitamins in dairy cows

Background: There is insufficient evidence in the literature concerning the fluctuations and correlations of serum fat-soluble vitamin concentrations during lactation in dairy cows and the potential effect of age of the animals on these values. Objectives: The objectives of this study were to determine fluctuations in mean serum concentrations of the fat-soluble vitamins A and E and beta-carotene and the correlations among them in clinically healthy dairy cows, from the last month of the dry period until the end of lactation, and to investigate whether age was a factor that affects these serum concentrations. Methods: Forty-five clinically healthy Holstein cows were assigned to 2 groups based on age. Group A consisted of 23 cows <= 4 years old (mean +/- SD, 3.24 +/- 0.44 years), and group B consisted of 22 cows >4 years old (6.68 +/- 1.66 years). Blood samples for determination of serum beta-carotene, vitamin A, and vitamin E concentrations were collected from each animal just before the start of study (1 month prior to expected parturition), at parturition, and thereafter, at monthly intervals until the end of lactation. Results: There was a significant positive correlation between beta-carotene, vitamin A, and vitamin E values. Mean serum concentrations of beta-carotene, vitamin A, and vitamin E were significantly higher in younger animals. Conclusions: To our knowledge, this is the first evidence that age is a factor affecting serum concentrations of fat-soluble vitamins in dairy cows.