Lactation Biology 2

The objective was to evaluate the effects of feeding level (FL) and milking frequency (MF) in early lactation on milk production in grazing dairy cattle. Multiparous Holstein-Friesian cows (n = 120; ~31 DIM) offered an unrestricted allowance of fresh pasture (UnRes) and milked twice daily (2X) were randomly assigned to one of 4 treatments for 21 d in a 2 by 2 factorial arrangement 2 FL of pasture (UnRes or a 50% restriction: Res) and 2 MF (once daily: 1X or 2X). After the treatment period, all animals received a generous allowance of pasture and were milked 2X for the remainder of lactation. Body weights (BW) and body condition scores (BCS) were recorded and milk samples collected once weekly. Main effects and interactions during treatment, and for 8 wk post-treatment, were tested using mixed models (GenStat 12.1). Interactions between FL and MF were detected (P < 0.01) for milk and protein yields during the treatment period. Decreases due to 1X were greater (P < 0.01) in UnRes than in Res cows for milk (4.8 vs. 2.2 kg/d), and protein (0.17 vs. 0.06 kg/d) yields. Upon cessation of treatments milk production was greater (P < 0.01) in UnRes cows compared with Res cows (18.4 vs. 17.1 kg/d) and in 2X compared with 1X (18.3 vs. 17.2 kg/d), but there was no interaction. Similarly, UnRes cows had greater (P < 0.01) fat (0.79 vs. 0.74 kg/d) and protein (0.67 vs. 0.62 kg/d) yields and 2X cows had greater (P < 0.01) fat (0.78 vs. 0.75 kg/d) and protein (0.66 vs. 0.63 kg/d) yields. Relative to their UnRes comparison, Res cows were lighter and thinner (P < 0.01; BW: 440 vs. 484 kg and BCS: 3.86 vs. 4.03; 10-point scale) and relative to 1X, 2X cows were lighter (P < 0.01; 460 vs. 468 kg) by the end of the treatment period. In summary, reducing milking frequency and the level of nutrition for 21 d in early lactation impaired milk production.