# Presentation: 734897

## 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 h2 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 h2

**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 1st lactation and included AI 1st 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 chi2 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 Ni = number of inseminations in the herd-year performed on the ith weekday (i=1,7), and HS is herd size.  Herd-years were grouped into 8 categories based on CHI and defined in Table 1.

|  | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 |
| --- | --- | --- | --- | --- | --- | --- | --- | --- |
| Criteria | 400  CHI  | 400  CHI   300 | 300  CHI   200 | 200  CHI   100 | 100  CHI   70 | 70  CHI   40 | 40  CHI   20 | CHI  20 |
| N. Herds | 362 | 567 | 1071 | 1309 | 1987 | 2053 | 2487 | 1253 |
| N. Cows | 36,106 | 46,291 | 103,801 | 142,900 | 149,196 | 140,914 | 144,400 | 141,866 |
| N. Records | 47,926 | 55,529 | 130,218 | 199,753 | 194,307 | 207,667 | 209,745 | 269,262 |

|  | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 |
| --- | --- | --- | --- | --- | --- | --- | --- | --- |
| Error Var. | 5,166 | 5,231 | 5,211 | 5,137 | 4,976 | 4,929 | 4,923 | 4,771 |
| PE Var. | 506 | 316 | 282 | 267 | 367 | 419 | 440 | 469 |
| Genetic Var. | 154 | 127 | 179 | 171 | 163 | 165 | 198 | 198 |
| Phenotypic Var. | 5,826 | 5,674 | 5,672 | 5,576 | 5,506 | 5,514 | 5,561 | 5,438 |
| h2 (%) | 2.6 | 2.2 | 3.2 | 3.1 | 3.0 | 3.0 | 3.6 | 3.6 |
| Repeatability (%) | 11.3 | 7.8 | 8.1 | 7.9 | 9.6 | 10.6 | 11.5 | 12.3 |

-                                       7
-  CHI = 100 * { [Ni – E(Ni)]2/E(Ni)}/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.