UC Davis

The effect of postpartum milking strategy on plasma minerals concentration, blood β-hydroxybutyrate (BHB) concentration, and colostrum, transition milk, and 1^st monthly test milk yield and composition was evaluated in 90 multiparous Jersey and Jersey × Holstein crossbreed cows from a commercial farm. Before 1^st postpartum milking cows were randomly assigned to: twice-a-day milking (M2; standard industry practice, milking every 12 h; n = 22), once-a-day milking (M1; milking every 24 h; n = 24), restricted milking (MR; 3 L milking every 12 h; n = 21), and delayed milking (MD; no milking for the first 24 h, and milking every 12 h afterwards; n = 23) strategies implemented during the first 2 d postpartum. Blood samples for total plasma Ca, P, and Mg determination were collected from enrollment every 4 h up to 48 h, and at 3 days in milk (DIM). Blood BHB concentration was determined at 3 and 11 DIM. Colostrum and transition milk yields were recorded, and samples were collected at each study milking for IgG and somatic cell count (SCC) determinations. Information for 1^st monthly test milk yield and composition was obtained from the Dairy Herd Improvement Association. Statistical analyses were conducted using generalized multiple linear and Poisson regressions with Dunnett adjustment and M2 as reference group for mean comparisons. Overall, plasma Ca concentration within 48 h post-enrollment was higher for MD (2.17 mmol/l), tended to be higher for MR (2.15 mmol/L), and was similar for M1 (2.09 mmol/l) compared to M2 cows (2.06 mmol/L). No statistically significant differences to M2 cows were observed for plasma P and Mg concentrations. Colostrum and transition milk, and total Ca harvested within 48 h post-enrollment were lower for M1, MR, and MD compared to M2 cows. The MD strategy prevented harvesting colostrum with >50 g IgG/L. No statistically significant effects were detected on plasma minerals concentration at 3 DIM, blood BHB concentration, colostrum and transition milk SCC within 48 h post-enrollment, or milk yield, energy-corrected milk yield, and SCC at 1^st monthly test. Our results suggest that postpartum plasma Ca concentration may be influenced by postpartum milking strategy, without interfering with future milk yield and udder health. Further studies need to be conducted to evaluate if the proposed milking strategies in early postpartum have an impact on production, reproduction, or health.