|Wright, Janice - Jan|
Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/26/2005
Publication Date: 1/1/2006
Citation: Hare, E., Norman, H.D., Wright, J.R. 2006. Trends in calving ages and calving intervals for dairy cattle breeds in the United States. Journal of Dairy Science. 89(1):365-370. Interpretive Summary: Utility of dairy cattle is influenced by age at first calving and calving interval. Calving ages and intervals and their trends over time were documented for US Ayrshires, Brown Swiss, Guernseys, Jerseys, and Holsteins. Age at first calving has declined and was 24 mo for Jerseys and 28 mo for Ayrshires in 2004. Mean age of US dairy cattle has declined sharply, apparently because of more intense culling. Calving interval has increased steadily and ranges from 390 to 407 d. Perhaps this trend will subside as more producers use the new genetic evaluation for daughter fertility.
Technical Abstract: Trends since 1980 for calving age and calving interval, two factors that influence herd life, were examined by parity for 5 breeds of US dairy cattle. Calving data were from cows with records that passed edits for USDA genetic evaluations and were in herds that remained on Dairy Herd Improvement test. First-calf heifers continued to calve earlier, but the age decline over time was less for later parities because of longer calving intervals. Breed differences for calving age were evident for all parities; current mean age at first calving ranged from 24 mo for Jerseys to 28 mo for Ayrshires. Mean calving age across all parities declined over time for all breeds and ranged from 48 mo for Holsteins to 54 mo for Ayrshires. Reductions in mean calving age for each breed resulted primarily from increased culling rate. Across parity, annual increase in calving interval was reasonably consistent (0.90 to 1.07 d/yr) for all breeds except Jersey (0.49 d/yr). Within parity, regressions of calving interval on year were generally similar to overall breed trend. Breed means for first calving interval across time ranged from 390 d for Jerseys to 407 d for Brown Swiss.