A multisite, randomized, controlled field study of a prepartum cholecalciferol injection on milk production, uterine health, blood minerals, and vitamin D metabolites in multiparous dairy cows.

The objective of the present study was to evaluate the effect of a prepartum injection with 10 × 106 IU cholecalciferol on milk production, uterine health, serum total calcium concentration (tCa) and vitamin D metabolites in a multisite setting, on farms feeding a prefresh diet with a positive DCAD. The study was conducted on 11 farms in northwestern Germany. Cows at the end of their first or greater lactation (n = 446) were randomly assigned to a treatment or a control group. Seven days before calving, cows of the treatment group received 10 × 106 IU (10 mL) of cholecalciferol, whereas cows of the control group received 10 mL of saline, intramuscularly. In a subsample of 95 cows, the concentrations of tCa, inorganic phosphate (Pi) and Mg were measured at 1, 2, and 3 DIM. In 30 of these cows, cholecalciferol, 25-OHD3, 1,25-dihydroxycholecalciferol (1,25-(OH)2D3), and 24,25-dihydroxycholecalciferol (24,25-(OH)2D3) concentrations were determined 2 d after injection and on 1, 2, and 3 DIM. At calving, cows were monitored for calving ease and stillbirth, and cows were examined for early postpartum diseases (retained fetal membranes [RFM], clinical hypocalcemia, metritis) until 10 DIM. Repeated measures ANOVA was performed to evaluate the effect of treatment on milk yield over the first 5 test days after calving, blood minerals, and vitamin D metabolites. A logistic regression model was calculated to evaluate the effect of treatment on RFM and metritis. Evaluating milk production over the first 5 test days, there was no difference in milk yield between cholecalciferol treated and control cows. No difference was observed between treated and control cows with regard to gestation length, calving ease, clinical hypocalcemia, and metritis. However, cows treated with cholecalciferol had a greater risk of incurring RFM after treatment with cholecalciferol (odds ratio = 2.12). Cows treated with cholecalciferol had slightly higher serum tCa concentrations with a maximum difference of 0.1 mmol/L at 1 DIM. Furthermore, cows in the treatment group had elevated serum Pi and decreased Mg concentrations over the first 3 DIM. The concentrations of cholecalciferol, 25-OHD3, 24,25-(OH)2D3 were increased already 2 d after cholecalciferol treatment and remained higher until 3 DIM, compared with control cows. Although the cholecalciferol concentration decreased considerably after calving, the concentrations of 25-OHD3 and 24,25-(OH)2D3 remained around 200 ng/mL, and 20 ng/mL over the first 3 d after calving, respectively. In contrast, the concentration of 1,25-(OH)2D3 was elevated 2 d after treatment, but decreased after calving, compared with control cows. Overall, in cows fed with a positive DCAD ration prepartum, there were only minor effects of treatment on blood tCa status.