title: Once-daily milking during a feed deficit decreases milk production but improves energy status in early lactating grazing dairy cows.
abstract: The objective of this study was to investigate the effect of milking frequency (MF) at 2 feeding levels (FL) on milk production, body condition score, and metabolic indicators of energy status in grazing dairy cows during early lactation. Multiparous Holstein-Friesian and Holstein-Friesian × Jersey cows (n=120) grazed pasture and were milked twice daily (2×) from calving until 34 ± 6 d in milk (mean ± standard deviation). Cows were then allocated to 1 of 4 treatments in a 2 × 2 factorial arrangement. Treatments consisted of 2 FL: adequately fed [AF; 14.3 kg dry matter intake (DMI)/cow per d] or underfed (UF; 8.3 kg of DMI/cow per d) and 2 MF: 2× or once daily (1×). Treatments were imposed for 3 wk. After the treatment period, all cows were offered a generous pasture allowance (grazing residuals >1,600 kg of dry matter/ha) and milked 2×. During the 3-wk treatment period, we observed an interaction between FL and MF for energy-corrected milk (ECM), such that the decrease due to 1× milking was greater in AF than in UF cows (20 and 14% decrease, respectively). No interactions were found posttreatment. Cows previously UF produced 7% less ECM than AF cows during wk 4 to 12; however, no subsequent effect was observed of the previous underfeeding. Cows previously milked 1× produced 5% less ECM during wk 4 to 12, and differences remained during wk 13 to 23. During the 3-wk treatment period, UF cows lost 0.2 body condition score units (1-10 scale) and this was not affected by 1× milking. During the treatment period, UF cows had lower plasma glucose, insulin, and insulin-like growth factor I, and greater nonesterified fatty acids and β-hydroxybutyrate concentrations than AF cows. Cows milked 1× had greater plasma glucose, insulin, and insulin-like growth factor I, and lower nonesterified fatty acids and β-hydroxybutyrate concentrations compared with cows milked 2×. In conclusion, energy status was improved by 1× milking; however, when UF cows were milked 1×, milk production was reduced by more than underfeeding alone. The immediate and residual responses to 1× milking need to be considered when using this management strategy during a feed deficit.
authors.affiliation: DairyNZ Ltd., Private Bag 3221, Hamilton 3240, New Zealand. Electronic address: jane.kay@dairynz.co.nz.
authors.forename: J K
authors.initials: JK
authors.lastname: Kay
authors.forename: C V C
authors.initials: CV
authors.lastname: Phyn
authors.forename: A G
authors.initials: AG
authors.lastname: Rius
authors.forename: S R
authors.initials: SR
authors.lastname: Morgan
authors.forename: T M
authors.initials: TM
authors.lastname: Grala
authors.forename: J R
authors.initials: JR
authors.lastname: Roche
mesh_terms: D020155:3-Hydroxybutyric Acid / Q000097:blood; D000821:Animal Feed; D000818:Animals; D002417:Cattle; D003612:Dairying; D004734:Energy Metabolism; D005230:Fatty Acids, Nonesterified / Q000097:blood; D005260:Female; D060434:Herbivory / Q000502:physiology*; D007328:Insulin / Q000097:blood; D007334:Insulin-Like Growth Factor I / Q000032:analysis; D007774:Lactation / Q000502:physiology*; D008892:Milk / Q000378:metabolism*; D010298:Parity
chemical_list: D005230:Fatty Acids, Nonesterified; D007328:Insulin; D007334:Insulin-Like Growth Factor I; D020155:3-Hydroxybutyric Acid
keywords: energy balance; milk production; nutrition; once-daily milking