New measure of bull fertility available

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Did you notice something different when you looked at the latest sire proof data?

If not, you should have. The new Sire Conception Rate (SCR) measurement was unveiled with the August proofs and is based on conception rate rather than a 70-day non-return rate.

The SCR is a more accurate measurement than the previous Estimated Relative Conception Rate (ERCR), says Duane Norman, research leader with the USDA Animal Improvement Programs Laboratory in Beltsville, Md. “SCR also features higher reliability since it uses multiple services per lactation (up to seven) rather than first service only. This triples the data.”

The tool also features data from three of the four major dairy records-processing centers — a major enhancement from previous evaluations that makes the evaluation national in scope.

Combine that with a tweaked computer model, and the tool offers increased accuracy in bull-fertility measurements — and a means to improve the fertility of your overall reproductive program. Here’s how to use it.

1. Generate bull list

Using your selection criteria, like net merit, generate a list of bulls to evaluate. Rank them according to how they fit your dairy’s (and individual cow) needs.

2. Evaluate bull fertility.

Next, take a look at how well the bulls score using the SCR.

You use this measurement similarly to how you used ERCR. The exception is that SCR is reported with one decimal place.

SCR evaluations are expressed as deviations from the breed average. For example, a SCR of 1.2 percent means that the bull is 1.2 percent above breed average. A SCR of -1.2 percent means that he is 1.2 percent below breed average, and a score of 0.0 means he’s at breed average.

To put this in conception-rate terms, a bull with an SCR of 2.0 percent is expected to produce a conception rate of 32 percent in a herd that normally averages 30 percent and historically used average conception-rate bulls, explains Norman.

3. Select bulls

Now that you know what these bulls will do for your herd’s fertility, select bulls to use on your dairy that fit your overall selection criteria and offer increased fertility. Remember that while this tool will help improve your reproductive program, you must still follow proper semen storage, handling and breeding techniques. 

Which bulls will receive a SCRrating?

The new sire conception rate scores will be available for bulls that have active A.I. status and are less than 13 years old. 

Holstein bulls must have at least 300 total breedings, with 100 breedings in the most recent 12 months in at least 10 herds, to quality for this evaluation. Evaluations for other breeds will also be available, though the minimum number of matings and herds will be somewhat less due to smaller animal populations.

Return rate vs. conception rate

Previously, bull fertility evaluations were based on 70-day non-return rates. that means, if a cow was not resubmitted for insemination 70 days after that first breeding, she was assumed pregnant. These data were factored into a bull’s Estimated Relative Conception Rate.

One problem with this is that a cow may be returned for insemination after day 70, like day 72, for example. However, the initial mating was still considered a success because she had not required breeding before day 70, says Duane Norman, research leader with the USDA Animal Improvement Programs Laboratory in Beltsville, Md.

The new Sire Conception Rate uses cow conception rate as the basis for its analysis, which increases data accuracy. “A cow must be pregnant using this measurement,” says Norman. This reduces the false positives that were possible with 70-day non-return rates.

The two traits are highly related when derived from the same cows, so the change won’t affect bull fertility rankings too much, he adds, but the additional inseminations do increase data reliability considerably.



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