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Effect of 25-hydroxyvitamin D3 [25-(OH)D3] on dairy cows.

H. M. Golder




Effect of 25-hydroxyvitamin D3 [25-(OH)D3] on dairy cows.
H. M. Golder*, I. J. Lean. Scibus Camden, NSW, Australia.

Subclinical hypocalcemia prevalence remains high postpartum despite use of negative DCAD diets and vitamin D3. We hypothesized that feeding 25-(OH)D3 (25D) during lactation, and in transition in conjunction with negative DCAD diets, would improve milk production, reproduction, and health. Dairy cows were used in 2 randomized exposure experiments. Experiment 1; cows in Control [CON; n = 645; no 25D] or Treatment [TRT; n = 537; 2 mg/d of 25D prepartum and 1 in lactation] groups assigned and fed from ~21 d prepartum were monitored for milk yield and composition, and health and reproductive measures. Experiment 2; 4 groups of cows (median 147 DIM) were monitored per Experiment 1 to the end of that lactation (L1), subsequent transition and lactation (L2). Groups were (1) CON-CON (no 25D), (2) TRT-TRT (1 mg/d of 25D in L1 and L2 and 2 prepartum), (3) CON-TRT (1 mg/d of 25D in L2 and 2 prepartum), and (4) TRT-CON (1 mg/d of 25D in L1). For L1, 1,032 cows entered control groups 1 or 3 and 1,032 in groups 2 or 4. The n/group that entered L2 was 521, 523, 273, and 248, respectively. Analysis used mixed linear and survival models (STATA V15, Statcorp LP, College Station, TX). Blood Ca, P, and 25D concentrations (n = 17/group) were evaluated at 5 times. Experiment 1, TRT cows had 0.2 lower LN SCC than CON cows (P = 0.002) and multiparous (multi) TRT cows had 41.1 � 23.4% (95% CI = 2.0—95.3%) higher odds of pregnancy/d than multi CON cows, reducing days open by a median of 22 d. Primiparous TRT cows had 1.67 � 0.40 times greater odds of mastitis/d than primiparous CON cows. In Experiment 2, TRT-TRT cows had 15.5—28.9% lesser odds to be bred/d than other groups (P = 0.016). Multi CON-CON and TRT-CON cows had 21.4 � 7.8% and 30.3 � 16.6% greater odds of pregnancy, respectively, than multi TRT-TRT cows. Serum Ca concentrations were not affected by group (P = 0.988), P (P = 0.003) and 25D concentrations (P < 0.001) were highest in the TRT-TRT cows. Duration on transition diet improved many measures of production, health and reproduction. While treatment lowered SCC and provided other benefits, particularly for multi cows including the time to pregnancy, responses varied across treatment groups.

Keywords: calcidiol, calcium, prepartum.