1. Assessment of voluntary waiting period and frequency of estrus synchronization among herds R.H. Miller, 1, * H.D. Norman, 1 M.T. Kuhn, 1 and J.S. Clay 2 1 Animal Improvement Programs Laboratory, Agricultural Research Service, USDA, Beltsville, MD 20705-2350 2 Dairy Records Management Systems, Raleigh, NC Abstr. W172 INTRODUCTION New reproductive management regimes adopted in recent years  Synchronization protocols (ES)  Timed insemination Voluntary waiting period (VWP) of 60 d assumed by USDA for genetic evaluation of pregnancy rate Actual herd VWP and frequency of ES relative to traditional estrus detection need to be examined OBJECTIVES Determine variation in DIM at first service after calving (DFS) among and within herds to assess consistency of VWP Identify ES herds with timed insemination and compare DFS and number of services between ES herds and those with traditional estrus detection DATA 5.55 million lactation records (DRMS, AgSource)  Inseminations from 1995 through August 2002  Identified service sires  Holsteins and Jerseys  Pregnancy status unknown 2529 herds on continual test from 1995 through 2001 Mean DFS and cows per herd CONCLUSIONS VWP Determination Increase in mean DFS from 89 d in 1995 to 94 d in 1998 and then slight decrease Within herd, reasonably consistent herd means for DFS from year to year (correlation = 0.67) 10% of cows inseminated before 60 DIM for 70% of herds  60-d VWP assumed by USDA for calculating pregnancy rate is conservative Increase in VWP since 1995, but recent moderation ES Herd Identification Strong trend toward ES/timed AI regimes relative to traditional estrus detection Steady increase from 0.9% in 1995 to 7.1% in 2001 in relative frequency of ES regimes (probable and ES) Fewer DFS (16.4 d) and days open (9 d) for ES herds than for herds with traditional estrus detection but more services per cow (0.18) METHODS VWP Determination Tabulate frequency distribution of herd-years based on DIM by which 10% of cows within herd-year received first insemination after calving  30 d   60 d   120 d  40 d   75 d   150 d  50 d   90 d Evaluate consistency of DFS within herd over time by intraclass correlation for herds on continual test ES Herd Identification Calculate  2 for each herd-year to determine whether frequency of first insemination deviated from equal distribution among 7 week days Evaluate effect of ES on days open available from lactation records in USDA national database  Not an ES herd 22 <22.46  Possible ES herd22.46 22 <100  Probable ES herd 100 22 <250  ES herd 22  250 RESULTS VWP Determination Cumulative frequency of herd-years based on DIM by which 10% of cows received first insemination after calving  Over 70% of herds with 10% of cows first inseminated by 60 DIM  Percentage of herds that had 10% of cows first inseminated by 60 DIM Intraclass correlation of 0.67 for DFS and 0.54 for number of services ES Herd Identification Mean cows per herd by herd ES status Within-year frequencies (%) of herd groups based on likelihood of ES Least-squares differences within herd among ES herd-year groups for DFS and NS Least-squares differences within herd among ES herd-year groups for days open 199519992001 Herd frequency (%) 77.570.572.3 Not ES Possibly ESProbably ESES 64 119203384 Year Not ES Possibly ES Probably ES 199591.28.00.80.1 199888.110.21.30.4 200177.215.74.42.7 Variable Not ES Possibly ES Probably ES DFS0.0  6.3  12.3  16.4 No. of services 0.000.070.090.18 Days open Not ES Possibly ES Probably ES Verified n=44,964 0.0  0.5  3.9  8.9 All data n=57,643 0.0  0.7  5.1  9.0 FUTURE RESEARCH Studies underway to determine if reproductive regime should be considered in genetic evaluations of pregnancy rate