Milk production of Holstein-Friesian, Jersey and crossbred cows milked once-a-day or twice-a-day in New Zealand

The objective of this study was to compare Holstein-Friesian (F), Jersey (J) and crossbred (F x J) cows milked once-a-day (OAD) or twice-a-day (TAD) in New Zealand for milk, fat and protein yield, lactation persistency and average somatic cell score (SCS). Data consisted of 223,149 herd-test records (89,297 and 133,852 OAD and TAD, respectively) from 11,848 F; 11,677 J and 27,720 F x J spring-calving cows between 2008 and 2012. Compared to TAD systems, cows milked OAD yielded 722, 28.0 and 22.2 kg less milk, fat and protein, respectively. Crossbred and J cows were less affected than F cows by OAD milking with a reduction in milk yield traits of <= 19.0%, while in F cows the reduction ranged between 19%-25%. Cows milked OAD had higher SCS than cows milked TAD (6.20 vs. 6.08). The greatest SCS difference in OAD and TAD systems was in first-lactation cows (6.40 vs. 6.02). Persistency of production traits was greater in F and F x J cows milked OAD than in F and F x J cows milked TAD, but J cows had similar milk and protein persistency in both systems. Overall, cows milked OAD had greater persistency than cows milked TAD (79%-90% vs. 76%-85%). These results show that, in commercial herds, the relative difference in production traits between OAD and TAD systems was smaller than those reported in experimental trials.