Temporary alterations to postpartum milking frequency affect whole-lactation milk production and the energy status of pasture-grazed dairy cows

This study investigated the immediate and long-term effects of temporary alterations to postpartum milking frequency (MF) on milk production, body condition score (BCS), and indicators of energy status in pasture-grazed cows supplemented with concentrates. Multiparous Holstein-Friesian cows (n = 150) were randomly assigned to 1 of 5 groups at calving: milked twice daily (2x) throughout lactation (control), or milked either once daily (1x) or 3 times daily (3x) for 3 or 6 wk immediately postpartum, and then 2x for the remainder of lactation. During wk 1 to 3 postpartum, cows milked 1x produced 15% less milk and 17% less energy-corrected milk (ECM) than cows milked 2x. This immediate production loss increased to 20% less milk and 22% less ECM during wk 4 to 6 postpartum for cows that remained on 1x milking; these animals also produced less than 1x cows switched to 2x milking after 3 wk. During wk 8 to 32, when all cows were milked 2x, those previously milked 1x had sustained reductions in milk (-6%) and ECM (-8%) yields, which were not affected by the duration of reduced postpartum MF. In contrast, cows milked 3x postpartum had 7% greater milk yields during wk 1 to 6 compared with 2x controls, irrespective of the duration of increased MF. Milk yields also remained numerically greater (+5%) during wk 8 to 32 in cows previously milked 3x. Nevertheless, yields of ECM were not increased by 3x milking, because of lower milk fat and protein contents that persisted for the rest of lactation. In addition, indicators of cow energy status reflected an increasing state of negative energy balance with increasing MF. Cows milked 1x postpartum had greater plasma glucose and lower plasma nonesterified fatty acid concentrations during the reduced MF, and plasma glucose remained lower for 2 wk after cows had switched to 2x milking. Moreover, BCS was improved relative to 2x controls from wk 5 to 6. In contrast, cows milked 3x had lower plasma glucose concentrations, greater plasma nonesterified fatty acid concentrations, and greater BCS loss during wk 1 to 3; however, greater body fat mobilization was not sustained, indicating that additional energy supplements may be required to achieve better milk production responses. In conclusion, temporary 1x milking had lactation-long negative effects on milk and milk component yields but improved cow energy status and BCS, whereas temporary 3x milking immediately increased milk yield but did not improve milk fat and protein yields in pasture-grazed cows.