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Genetic thresholds vs. genetic plans when selecting sires

Chrissy Meyer Published on 30 June 2015

“Give me a bull that’s over 1,300 kilograms of milk and positive for DPR.”

Does this sound like you describing sire selection criteria for your dairy? If so, you are among many dairy producers who are leaving extra kilograms of milk and additional pregnancies on the table.

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The traditional threshold method can be a risky approach to selecting bulls when you are aiming to maximize genetic progress.

Setting a minimum level for any given trait and completely eliminating sires that fall short of those minimums means you could be missing out on a number of bulls that could actually help propel your genetic level to new heights.

A genetic threshold versus a genetic plan

Take, for example, the old-fashioned threshold method for choosing the bulls you pick. If you direct your A.I. rep to drop off five bulls that have an EBV more than 1,300 for milk and more than 0.0 for DPR, he may leave you with the following group of sires (Table 1).

genetic threshold selectionSince your A.I. rep did his job and followed your wishes, you can see the averages for milk and DPR are pretty good – even above your set thresholds. But is that really the best group of bulls you can get?

If you reset your thought process for sire selection, you can choose to set a genetic plan that aligns with your goals.

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The previously mentioned thresholds would equate to a genetic plan with about 50 percent emphasis on production traits, 50 percent emphasis on health traits and 0 percent emphasis on conformation or type traits.

By using this 50-50-0 genetic plan for selecting your bulls rather than limiting yourself by thresholds, you could end up with a genetic package like the following five bulls (Table 2).

genetic plan selectionNot even one of these five bulls fit both the criteria of being more than 1,300 kilograms of milk and being positive for DPR, but you can see they just barely miss the mark on one trait or the other.

Looking at Sire F, you’ll notice that by sacrificing 53 kilograms of milk below your threshold, you gain an extra 4.3 points for DPR. And even though Sire I falls 0.3 short on his DPR value, he provides well over double the kilograms of milk your thresholds would have dictated.

So if you look at the average genetics of this group, they are well above and beyond what you achieve with the group of sires that meets both criteria.

In this case, by setting a genetic plan to select your bulls, you will gain nearly 530 extra kilograms of milk and nearly a 1.5 percent higher pregnancy rate than by stating clear-cut threshold limits.

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Tables 1 and 2 illustrate that setting a genetic plan to put emphasis on the traits that matter to you can boost your genetic levels well beyond what you achieve with restrictive thresholds.

Genetic plans – not just for sire selection

When setting a genetic plan, the most common focus is on sire selection. However, with genomic testing and various reproductive technologies readily available, many dairy farmers also rank females to determine which cows or heifers should receive sexed semen versus convention semen or which animals are the best candidates to flush versus which should serve as recipients.

If you rank your heifers and cows, it is important to remember to use the same genetic plan on the female side as you use for selecting your sires. Otherwise, you will lose the full effect of the genetic progress you could make with the sires you select.

If you select your sires based on a genetic plan of 50 percent production, 50 percent health and 0 percent type, but then rank females by LPI, Pro$ or a completely different index, your overall genetic progress toward your goals will suffer. A mixed approach will slow your progress and lessen your results.

In a nutshell

Maximize genetic progress in your herd by setting your own customized genetic plan to emphasize the traits that matter to you rather than limiting your options with strict trait thresholds.

To drive your genetic progress even further, make sure the genetic plan you put in place for sire selection matches the one you also use to rank your females.  PD

Chrissy Meyer
  • Chrissy Meyer

  • Marketing Editor
  • Alta Genetics
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