# Presentation: 864796

## Comparison of maturity rate for bull daughters in the United States and Canada

- RESULTS

*H.D. Norman**1**, J.R. Wright**1**,* R.L. Powell**1**, P.M. VanRaden**1**, and F. Miglior**2,3*
- 1Animal Improvement Programs Laboratory, Agricultural Research Service, USDA, Beltsville, MD 20705-2350
- 2Agriculture and Agri-Food Canada – Dairy and Swine Research and Development Centre, Lennoxville, QC, Canada
- 3Canadian Dairy Network, Guelph, ON Canada

- Abstr. M20

- INTRODUCTION
- Many countries in Interbull calculate genetic evaluations for individual parities to consider differences in rate of maturity.
- In Canada, genetic evaluations are calculated with a multi-trait parity model.
- In the U.S., official genetic evaluations are calculated  with a single-trait repeatability model.
- Recent U.S. studies show that apparent differences in maturity rate of bulls’ daughters are contributing to variation in USDA PTAs across time.
- Examining apparent differences in rate of maturity in two populations should provide evidence to determine whether the observed differences are genetic.

- OBJECTIVES
- Compare apparent differences in maturity rate of bulls’ daughters across countries to determine if they are consistent.

- DATA & METHODS *(cont.)*
- Canada data:
- Estimated Breeding Values (EBV) from published November 2004 CDN evaluation using test day model converted to predicted transmitting ability (divided by 2)
- Standardized first parity (CAN1)
- Standardized second parity (CAN2)
- Standardized third parity (CAN3)
- Methods
- Genetic evaluation subsets:
- Analysis was run on three groups of bulls:
-  20 or more daughters in both countries
-  			(804 bulls)
-  100 or more daughters in both countries
- 			(403 bulls)
-  500 or more daughters in both countries
-  			(131 bulls)

- RESULTS *(cont.)*
- Correlations between parity differences were highly related to number of daughters and records included.
- Evaluations of parities with the highest genetic correlations had the lower correlations between their differences across countries

- CONCLUSIONS
- Correlations between genetic evaluations from the two countries were high.
- Differences in apparent rate of maturity observed were highly correlated, providing convincing evidence that the differences observed are genetic.

- DATA & METHODS
- US data:
- Three predicted transmitting abilities (PTA) were created using current USDA-DHIA animal model methodology
- Data were Holstein cows first calving 1960-1998
- PTAs included either first parity (US1,), first and second parity (US1,2), or first, second and third parity records (US1,2,3)
- Contributions of second and third parity alone (US2, US3) were derived from the other three by weighting for the numbers of daughters/records in each parity

| US |  |  |  |  | CANADA |  |  |
| --- | --- | --- | --- | --- | --- | --- | --- |
|  | US1 | US2 | US3 |  | CAN1 | CAN2 | CAN3 |
| US1 | 1.00 | 0.87 | 0.83 |  | 0.93 | 0.84 | 0.79 |
| US2 | 0.87 | 1.00 | 0.92 |  | 0.84 | 0.92 | 0.91 |
| US3 | 0.86 | 0.96 | 1.00 |  | 0.81 | 0.89 | 0.90 |
| CAN1 | 0.96 | 0.87 | 0.86 |  | 1.00 | 0.90 | 0.86 |
| CAN2 | 0.83 | 0.94 | 0.92 |  | 0.90 | 1.00 | 0.97 |
| CAN3 | 0.81 | 0.92 | 0.93 |  | 0.88 | 0.98 | 1.00 |

- Within birth year correlations between parity specific evaluations (bulls with >=100 daughters above the diagonal, those with >=500 below

-  Correlations were highest between parity 2 and 3 within (0.92 to 0.98) and across countries (0.89 To 0.92).
-  Correlations were lowest between parity 1 and 3 within (0.83 to 0.88) and across countries (0.79 to 0.86).
- Correlation were high between evaluations for the same parity across countries (0.90 to 0.96)
-  Correlations between Canadian parity EBVs were higher than between US parity PTAs, due in part to the genetic correlations matrix assumed between lactations.
-  Correlations observed between parities were considerably higher than those assumed in the evaluation model.
-  Regressions (not shown) were from 0.90 to 1.00, and slightly higher for US PTAs than for Canadian EBVs. Standard errors ranged from 0.01 to 0.04.

|  |  | Bull minimum no. of daus |  |  |
| --- | --- | --- | --- | --- |
| US
(no. of lactations) |  |      20  |     100  |      500  |
|  | Parity 1  | 3140 | 5007 | 9186 |
|  | Parity 2  | 2257 | 3588 | 6573 |
|  | Parity 3 | 1496 | 2360 | 4295 |
| Canada
(no. of test days) | Parity 1 | 11,555 | 19,985 | 45,923 |
|  | Parity 2 | 8,219 | 14,262 | 32,909 |
|  | Parity 3 | 5,927 | 10,290 | 23,988 |

- 					RESULTS
- Average number of lactations or test days

- Min. no. of
-  daus.		Trait differences			Corr.  Reg.
-   20	 US2 - US1 and CAN2 - CAN1 		0.63   0.63
-  		 US3 - US1 and CAN3 - CAN1 		0.53   0.55
- 		 US3 – US2 and CAN3 – CAN2		0.14   0.08
- 100		 US2 - US1 and CAN2 - CAN1 		0.81   0.83
- 		 US3 - US1 and CAN3 - CAN1 		0.75   0.78
- 		 US3 – US2 and CAN3 – CAN2 		0.24   0.14
- 500	 US2 - US1 and CAN2 - CAN1 		0.89   0.98
- 		 US3 - US1 and CAN3 - CAN1 		0.84   0.91
- 		 US3 – US2 and CAN3 – CAN2 		0.55   0.50