Effect of dietary thiamin supplementation on milk production by dairy cows.

We conducted three experiments to determine the effects of dietary thiamin supplementation on milk production by dairy cows. In trial 1, 28 Holstein cows were blocked by parity and assigned randomly to either placebo or thiamin top-dress for the 8-wk experiment to provide a supplemental thiamin intake of 0 or 150 mg/d per cow. Within each of these groups, cows were further assigned randomly to two total mixed rations (TMR) for 4 wk, with the TMR treatments then reversed for a second 4-wk experimental period. Milk yield was 2.7 kg/d higher for thiamin-supplemented cows. Yields of milk fat and protein were increased 0.13 and 0.10 kg/d, respectively, by dietary thiamin supplementation. In trial 2, 20 multiparous Holstein cows were used in a crossover design with 4-wk periods. Placebo or thiamin premixes were added to TMR to provide an approximate daily supplemental thiamin intake of 0 or 300 mg/cow. Milk and protein yields tended to be 0.7 and 0.04 kg/d higher, respectively, for thiamin-supplemented cows. In trial 3, 16 multiparous Holstein cows were used in a replicated 4 x 4 Latin square with 21-d periods. Placebo or thiamin premixes were added to TMR to provide an approximate daily supplemental thiamin intake of 0 or 300 mg/cow. Dry matter intake tended to be 0.8 kg/d lower for thiamin-supplemented cows. Milk fat percentage tended to be 0.18 percentage units lower and fat yield was 0.08 kg/d lower for thiamin-supplemented cows. Thiamin supplementation tended to increase milk and component production when dietary concentrations of neutral and acid detergent fiber were lower and nonfiber carbohydrate was higher than recommended.