No Single Trait Selection

The headline grabs attention. Who would want to use a single trait selection approach anyway – right? Over the years, many producers have singularly focused on one proof value or another. For example, the proof value for milk yield or perhaps Type. Some have practiced what could be construed as pretty close to a single trait selection approach. The theory is, to make rapid progress; you need to really focus on what you want to change. But does single trait selection even exist? The answer can be provided by saying “there’s no free lunch”. In genetic terms when you select or make progress on one trait, there are others as well that will be impacted – some helped, some hurt. The key is to know how the interrelationships work.

The table below provides a picture of how other traits are affected when the focus is put on one trait – even if that one trait is really a composite of many. It’s important to understand which traits will be influenced positively and which ones we will lose ground on. The starting point in this analysis is a listing of high reliability bulls – bulls for which there is sufficient accuracy, even for management traits like Productive Life (PL), Daughter Pregnancy Rate (DPR) and Health. By selecting from that group approximately the best 20% for TPI, NM$, PL, PTAT or Health, it is enlightening to see what traits are positively and negatively impacted.

Demonstrating the Interrelationship of Traits
(High Reliability Sires: = 95%Rel. P)

Aug 2004 Official US Proof Data

Conclusions to draw:

• Higher TPI impacts Production, Type, PL, SCS & Health positively, but has no impact on DPR.
• Selecting for higher NM$ provides a greater positive impact on Production – especially component yields, PL and DPR than selecting on TPI while leaving Type levels essentially unchanged. The degree of positive impact to Health is essentially the same with both approaches.
• Selecting for higher PL leaves Production and Type levels basically unchanged when compared to the entire group. On the other hand, the improvement to DPR and Health and of course PL trait averages is much greater.
• Selecting for higher Type is accompanied with a loss on Production trait averages and NM$. Moderate gains are generated for TPI and Health. This analysis would essentially say that breeding for Type has no impact on SCS, PL and if anything it appears to impact DPR negatively!
• Selecting for Health will negatively impact production gains - but not as much as when Type is the singular focus. Moderate Type improvement accompanies Health along with major gains for PL, SCS and DPR. Selecting for Health brings with it almost the same amount of gain on PL and DPR as selecting solely on PL. You give up a bit of production but gain quite an improvement in Udders and SCS.

Posted Nov 5th

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