Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/2/2006
Publication Date: 3/1/2007
Citation: Miller, R.H., Norman, H.D., Kuhn, M.T., Clay, J.S., Hutchison, J.L. 2007. Voluntary waiting period and adoption of synchronized breeding in Dairy Herd Improvement herds. Journal of Dairy Science. 90(3):1594-1606. Interpretive Summary: Voluntary waiting period (VWP) is a key management decision in which the herd manager designates a target number of days postpartum after which cows will be inseminated. One factor in choosing a VWP for lactating cows is that conception rate is expected to increase as days postpartum increase, which may be partly related to milk yield. No effect of level of milk yield on conception rate after timed artificial insemination has been found. Reducing VWP is tempting because of associated reductions in calving interval. However, cows that conceive too early during lactation may have to be dried off when milk yield is still relatively high. Synchronized breeding (ovulation synchronization followed by timed artificial insemination) may be beneficial in reducing days open and days to first service for herds with poor estrus detection. Voluntary waiting period and frequency of synchronized breeding were assessed from 5.6 million lactations from 1995 through 2001. Median VWP was <60 d. Proportion of herds using synchronized breeding at first service has grown from <1% in 1995 to 7% in 2001. Herds with synchronized breeding had fewer days to first service and fewer days open than did herds with traditional estrus detection. Accounting for reproductive management regimes when calculating genetic evaluations for pregnancy rate may improve accuracy of those evaluations.
Technical Abstract: Voluntary waiting period (VWP) and adoption of synchronized breeding (ovulation synchronization followed by timed artificial insemination) were characterized from 5.55 million lactations of Holsteins and Jerseys. Calving month and year, type of service (artificial insemination versus natural service), parity, and first test-day milk yield had large effects on days to first service for both breeds. Cows that calved during April and May were bred later than those that calved during other months, whereas cows that calved during September and October were bred earlier. First-parity cows were bred later than later-parity cows. Herd-year VWP was assumed to be the days postpartum by which 10% of cows had received a first insemination. Over 70% of herds had 10% of cows inseminated by 60 d postpartum, the VWP assumed for national evaluations for daughter pregnancy rate. Herd-years with synchronized breeding at first service were identified through chi-square analysis based on deviation of observed frequency of first services by day of week from an expected equal frequency. Herds with synchronized breeding had fewer days to first service (16.4) and fewer days open (9) than did herds with traditional estrus detection. Adoption of synchronized breeding for first services steadily increased from <1% of herd-years (3% of cows) for 1995 to 7.1% of herd-years (22% of cows) for 2001. Procedures for genetic evaluation of daughter pregnancy rate should be examined to determine if herd regime for reproductive management affects results.