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The Reliability Dilemma
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Reliability - is it a consideration when you choose sires for your breeding program? If you answered yes, there’s a good chance it was Production and Type reliabilities you were thinking of. But, what about reliability values for other traits? These days, management traits like Productive Life (PL), Somatic Cell Score (SCS), Calving Ease (CE) and Daughter Pregnancy Rate (DPR) are increasingly being used as selection criteria, yet little consideration is given to the significantly lower accuracy levels that accompany their genetic evaluations. Many of these management traits are considered very important in terms of their economic impact. Still, those same traits almost universally carry low heritabilities, resulting in low reliability levels until bulls are well into their careers. These traits are too important to ignore, but, the accuracy of prediction, especially for new emerging bulls, is too low to give much consideration. |
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So what should you do?
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Understand the Numbers
Productive Life – for sires with at least 100 milking daughters, reliability values remain low until a significant number of daughters have had a chance to start their second and third lactations. Actual culling information on first crop daughters for bulls like Throne, Four Star, Tomahawk, Adam, Karat, Merchant and Blastoff adds between 10 and 20% to their PL reliability level (that’s why it’s important to watch the PL trend for bulls when second lactation information begins to enter the proof). Ally, by comparison has plenty of daughters, but they are almost all still in their first lactation. The result is a 61% reliability compared to 81% for Throne who has many daughters in third lactation. When second crop daughters enter the milking string in large numbers – like for Marshall – the reliability figure for PL does not immediately increase significantly. These daughters also need to reach second and third lactation. Newly proven bulls like Rolex and Granado carry a reliability that is in essence a parent average.
Somatic Cell Score – for sires with at least 100 milking daughters, reliabilities rise quickly to a level sufficiently high to base selection decisions on. Second and third lactation data on remaining daughters adds another 5 to 10% in reliabilities such that prior to second crop daughters arriving on the scene the 80% reliability threshold can be achieved. Second crop daughters quickly push sires over the 90% reliability level.
Calving Ease – “Direct” Calving Ease ratings – a reflection of how easily a sire’s calves are delivered – achieve moderately high reliabilities immediately for well sampled bulls. More than a year after graduating to the marketing lineup, a wave of second crop calves being born will boost reliability levels over the 90% barrier quickly for high usage sires. “Maternal” Calving Ease ratings – a reflection of how easily a sire’s daughters themselves deliver calves – do not achieve high reliabilities until a significant number of second crop daughters are in milk. Quite frankly, while the trait may well be important economically, accurate information arrives too late to influence many sire selection decisions.
Daughter Pregnancy Rate – This new genetic trait is the industry’s response to fertility concerns that have been expressed by many dairy producers. There is no question that genetic differences in female fertility are extremely important economically, and so despite a low heritability, the trait should not be ignored. It is important once again to recognize that for newly proven sires, the DPR rating is essentially a parent average. Well sampled bulls with second and third lactation milking daughters will often add 10% to their original reliability level so it’s important to watch the trend. Still, a highly accurate assessment will not be achieved before significant numbers of second crop daughters themselves reach second lactation.
Expect More Re-Ranking of Bulls
No AI stud is immune to the increased re-ranking that will occur due to significant weighting of management traits in industry lists like TPI and NM$. At the outset of a proven sire’s career traits like PL, SCS, DPR and Maternal CE are essentially no more accurate than a parent average. Although SCS proof information quickly becomes more accurate, only well sampled bulls with daughters beyond first lactation generate high enough reliabilities to warrant usage of PL and DPR as selection criteria. And while parent averages do provide a good starting point, at times they assess bulls with an unwarranted “bonus” or “penalize” unjustly. Not all bulls that are sons of high PL sires will themselves transmit impressive resistance to culling – and the opposite is equally true. When reliabilities increase for management traits – that is to say when daughter information begins to replace parental contribution – expect some bulls to experience significant change to their TPI and especially NM$ values as a result. It’s the price we will pay for including these traits in our industry rankings.
An increased focus on management traits in our global breeding programs is a positive step. In the years to come it will assist producers in generating more trouble-free cows that last longer. Still, we have been slow to adjust in our sire selection approach, quickly incorporating new emerging sires as had been the pattern in years when only production and type trait evaluations were being considered. Management traits have low heritabilities. Reliability values start low and take a considerable amount of time to rise to a level where they will inspire confidence. That’s why bulls, having demonstrated through higher reliabilities that they indeed do transmit a desirable array of health and management traits, will enjoy increased popularity with astute dairy producers, so long as they are reasonably competitive in other areas as well.
It’s worth thinking about how reliability values influence your genetic selection approach. There’s more to consider than just Production and Type!
Posted Jan 16th
