title: Temporary alterations to postpartum milking frequency affect whole-lactation milk production and the energy status of pasture-grazed dairy cows.
abstract: 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 (2 ×) throughout lactation (control), or milked either once daily (1 ×) or 3 times daily (3 ×) for 3 or 6 wk immediately postpartum, and then 2 × for the remainder of lactation. During wk 1 to 3 postpartum, cows milked 1 × produced 15% less milk and 17% less energy-corrected milk (ECM) than cows milked 2 ×. This immediate production loss increased to 20% less milk and 22% less ECM during wk 4 to 6 postpartum for cows that remained on 1 × milking; these animals also produced less than 1 × cows switched to 2 × milking after 3 wk. During wk 8 to 32, when all cows were milked 2 ×, those previously milked 1 × 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 3 × postpartum had 7% greater milk yields during wk 1 to 6 compared with 2 × controls, irrespective of the duration of increased MF. Milk yields also remained numerically greater (+5%) during wk 8 to 32 in cows previously milked 3 ×. Nevertheless, yields of ECM were not increased by 3 × 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 1 × 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 2 × milking. Moreover, BCS was improved relative to 2 × controls from wk 5 to 6. In contrast, cows milked 3 × 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 1 × milking had lactation-long negative effects on milk and milk component yields but improved cow energy status and BCS, whereas temporary 3 × milking immediately increased milk yield but did not improve milk fat and protein yields in pasture-grazed cows.
authors.affiliation: DairyNZ, Private Bag 3221, Hamilton 3240, New Zealand. Electronic address: claire.phyn@dairynz.co.nz.
authors.forename: C V C
authors.initials: CV
authors.lastname: Phyn
authors.affiliation: DairyNZ, Private Bag 3221, Hamilton 3240, New Zealand.
authors.forename: J K
authors.initials: JK
authors.lastname: Kay
authors.affiliation: Department of Animal Science, The University of Tennessee, Knoxville 37996.
authors.forename: A G
authors.initials: AG
authors.lastname: Rius
authors.affiliation: DairyNZ, Private Bag 3221, Hamilton 3240, New Zealand.
authors.forename: S R
authors.initials: SR
authors.lastname: Morgan
authors.affiliation: DairyNZ, Private Bag 3221, Hamilton 3240, New Zealand.
authors.forename: C G
authors.initials: CG
authors.lastname: Roach
authors.affiliation: DairyNZ, c/o University of Auckland, 3A Symonds St, Auckland 1010, New Zealand.
authors.forename: T M
authors.initials: TM
authors.lastname: Grala
authors.affiliation: DairyNZ, Private Bag 3221, Hamilton 3240, New Zealand.
authors.forename: J R
authors.initials: JR
authors.lastname: Roche
mesh_terms: D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D002417:Cattle / Q000502:physiology*; D003612:Dairying / Q000379:methods*; D004734:Energy Metabolism; D005230:Fatty Acids, Nonesterified / Q000097:blood; D005260:Female; D007774:Lactation / Q000502:physiology*; D008892:Milk / Q000378:metabolism*; D049590:Postpartum Period / Q000502:physiology; D013997:Time Factors
chemical_list: D001786:Blood Glucose; D005230:Fatty Acids, Nonesterified
keywords: dairy cow; early lactation; energy status; milking frequency