1. Synchronization Effects on Parameters for Days Open M. T. Kuhn, J. L. Hutchison, and R. H. Miller* Animal Improvement Programs Laboratory, Agricultural Research Service, USDA, Beltsville, MD 20705-2350 Abstract M24 2006 CONCLUSIONS Developed a method to identify herds synchronizing based on frequency of first inseminations by day of week. Estimated genetic, PE, and error variances for DO within 8 CHI groups based on likelihood of practicing synchronization. Genetic variance in DO was greater in herds following traditional estrus detection than in herds practicing synchronization. Heritability of DO was higher (3.6%) in herds not synchronizing than in herds synchronizing (2.6%). Repeatability tended to be higher in herds not synchronizing than in herds synchronizing. Genetic correlation between DO in herds synchronizing and DO in herds not synchronizing was near 1.0. Future research will future explore how heterogeneous variance adjustment affects genetic evaluations for DO/DPR. MATERIALS & METHODS (con’t.) Analyses of CHI groups Analyses were conducted by REML within each of the 8 CHI groups using the model: DO = HY + Year-State-Month + Lact + PE + A + e, Where HY is herd-year, year and month of calving, Lact is parity number, PE is permanent environment effect, A is additive genetic effect, and e is error effect. The genetic correlation between DO in synch and non-synch herds was estimated using the program MTDFREML. Herds were randomly selected within CHI groups 4 through 8 for inclusion in statistical analysis. Over half the herds had 3 or fewer years of available data. Table 1 gives the criteria, number of herds, cows, and lactations for the 8 CHI groups. Table 1. Data included in statistical analyses. RESULTS Table 2. Single-trait variance estimates by CHI groups. Synchronization (groups 1-6) lowered genetic variance and heritability compared to non- synchronized DO (groups 7 & 8). Days to first breeding (DFB) has a higher h 2 than conception rate. Thus, synchronization is likely removing some genetic variance (in DO) related to DFB. Error variance also tended to be slightly higher where a greater degree of synchronized breeding (groups 1 through 4) was occurring. Synchronization generally lowered repeatability as well, although trend was less clear than for h 2 INTRODUCTION Use of synchronized breeding regimes is steadily increasing. While variations in protocols exist, many provide for timed AI rather than observation of estrus behavior. Fertility traits may be different genetically compared to traditional insemination based on observed estrus because expression of estrus behavior is no longer involved. To examine this question requires a method to identify herds practicing synchronization (synch). OBJECTIVES Develop a method to identify herds which practice (a) synchronization/TAI (b) insemination based on observed estrus. Estimate genetic and error variances for days open (DO) for alternative breeding practices. Estimate the genetic correlation between DO with and without synchronization MATERIALS & METHODS Holstein cows calving between 1995 to 2005, required to have a 1 st lactation and included AI 1 st services only. Assumed that herds practicing synch would deviate from an expected equal distribution of services among weekdays Sunday through Saturday. Synch vs. Non-synch Herd Identification Developed a chi 2 based statistic (CHI) whose magnitude for inseminations in a herd-year was expected to increase with increased likelihood of the herd practicing synch. The statistic is: where N i = number of inseminations in the herd-year performed on the i th weekday (i=1,7), and HS is herd size. Herd-years were grouped into 8 categories based on CHI and defined in Table 1. 12345678 Criteria 400  CHI400  CHI  300300  CHI  200200  CHI  100100  CHI  7070  CHI  4040  CHI  20CHI  20 N. Herds362567107113091987205324871253 N. Cows36,10646,291103,801142,900149,196140,914144,400141,866 N. Records47,92655,529130,218199,753194,307207,667209,745269,262 12345678 Error Var.5,1665,2315,2115,1374,9764,9294,9234,771 PE Var.506316282267367419440469 Genetic Var.154127179171163165198 Phenotypic Var.5,8265,6745,6725,5765,5065,5145,5615,438 h 2 (%)2.62.23.23.13.0 3.6 Repeatability (%)11.37.88.17.99.610.611.512.3 7 CHI = 100 * {  [N i – E(N i )] 2 /E(N i )}/HS, i=1 RESULTS (con’t.) The genetic correlations between DO for cows in CHI group 8 (non-synch) and DO for cows in the other 7 groups were near 1.0, indicating that DO can be considered the same trait regardless of synch. A further question is whether the differences in variances in Table 2 should be considered in genetic evaluations of DO/Pregnancy Rate. Preliminary results indicated only a slight improvement in sire PTA when DO records were adjusted for these differences.