Serum macromineral dynamics and milk production of old Holstein cows submitted to a postpartum delayed milking strategy

Lactation initiates with a massive Ca secretion into milk. Within 24-48 h post-calving, high-producing, older- parity dairy cows are highly susceptible to Ca disturbances. We hypothesized that the abrupt cessation of milking within this critical period would delay Ca secretion into milk, allowing lactating cows more time to stabilize their Ca homeostasis mechanisms and potentially lower the risk of blood Ca decline in the immediate postpartum period. After colostrum harvest, a total of 175 multiparous Holsteins (parity ranging from 3 to 7) were randomly assigned to three treatment groups: 1) control (n = 59), whereby cows were milked 3 times/day (M0), 2) the treatment whereby milking of cows was withdrawn for the first 24 h (M24; n = 60), and 3) for the first 48 h after calving (M48; n = 56). All cows were given two oral Ca boluses (31 g Ca/bolus), the first bolus was administered within 30-60 min after calving, and the second bolus was given 24 h later. After the delayed milking treatment, cows in M24 and M48 groups returned to M0 milking program. On d 2 and 3 post-calving, blood total Ca concentration was not different between M24 and M48 cows, but both groups had greater Ca concentrations than M0 cows. On day 2 post-calving, serum P concentration was greater in M48 compared to M24 and M0 (1.86 vs. 1.47 +/- 0.06 mmol/L). On d 3, M0 cows had lower P concentration than M24 or M48 cows. Despite a transient decline in milk production in M24- and M48-treated cows, both treatments attained a similar milk production level as they switched to M0 milking program. No difference existed in the first 3 monthly test- day milk records. The postpartum milking strategy had no impact on the culling risk by 120 DIM. These results support delaying milking for 24 and 48 h after colostrum collection to maintain Ca status in multiparous cows. Evaluation of the long-term effects of the delayed milking strategies on mammary health, reproduction performance, and survivability of pluriparous dairy cows is recommended.