Effect of herd by sire interaction variance on genetic evaluations

1. Effect of herd by sire interaction variance on genetic evaluations

2. Introduction • For almost 40 years, U.S. genetic evaluations have accounted for genotype-environment interaction. • The animal model includes a term for interaction effects of sire and herd. • Multiple daughters of a bull in the same herd have reduced weight.

3. History of Herd x Sire Effect • Magnitude of H x S variance (c2) estimated to be 14% in 1968 (Plowman and McDaniel JDS 51:306) • More recent research estimated c2 to be as low as 2% (Dimov et al, 1995 JDS 78:939) • As a result, c2 lowered to 10% in 1997.

4. Methods – November 2004 • Official November 2004 predicted transmitting abilities (PTA) for Holstein protein yield with c2 = 10% were compared with PTA computed with reduced c2 of 5% and 1%. • Repeatability of protein yield was held constant at 0.55 by increasing permanent environmental variance (p2) as c2 was decreased.

5. Herd × Sire Variance: Maximum Daughters / Herd

6. Herd x Sire Variance: Daughters / Herd 1% H×S 5% H×S 10% H×S

7. Mean PTA protein (kg)

8. Mean reliability protein (%)

9. Correlation with official PTA(c2 = 10%)

10. Summary:top 100 active AI bulls • With c2 reduced from 10 to 5% • 98 bulls had no change in PTA protein • 2 bulls had PTA changes of 1 kg • With c2 reduced from 10 to 1% • 92 bulls had no change in PTA protein • 8 bulls had changes of 1 or 2 kg

11. Summary:cows born since 1997 • Of 2.3 million recent cows, PTA protein changed >4 kg for: • 20 cows when c2 = 5% • 1256 cows when c2 = 1% • Cows changing the most were sired by non-AI bulls with many daughters in one or a few herds.

12. Implementation – May 2005 • H x S variance for yield traits was reduced from 10% to 7% of total. • Repeatability for yield traits was held constant at 55% by increasing permanent environmental variance (p2) from 15% to 18% of total. • For DPR, c2 was 1%, now is 4%.

13. May 2005 Herd × Sire Variances: Maximum Daughters / Herd

14. Herd × Sire Variance:Daughters / Herd 5% H×S 7% H×S 10% H×S

15. Changes from reducing c2 from 10% to 7% • 99 of the top 100 active AI bulls changed less than 1 kg PTA protein, only 1 bull changed 1 kg. • 597 cows changed >4 kg protein out of 2.3 million recent cows. • .999 correlation for both bulls and cows.

16. Foreign experience • Great Britain had herd-by-sire interaction in lactation model but not in test day model research. • Several single herd bulls rose towards the top, so a H x S effect was added back into the new test day model in May.

17. Conclusions • Reduction of c2 from 10% to 7% will facilitate AI companies obtaining more daughters per herd in large cooperating herds. • The H x S interaction protects against chance or fraud when sampling is limited to few herds.

18. Further study ideas • Use of a relationship matrix among herd by sire or herd by animal interactions could be helpful but was not tested in the current studies. • Interactions of sire or animal with region, climate, or country could be useful in the future.