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Finding fertile opportunity

Wes Ishmael for Progressive Cattle Published on 25 October 2021
Cow calf pair

“If you have a more fertile cow herd, the obvious benefit is: You have more calves to sell,” says Kent Andersen, director of technical services for global beef genetics at Zoetis.

“If reproduction is better, you’re getting more cows bred early and they calve earlier the next season. On average, calves born earlier are older and heavier when they’re marketed, and you have more uniformity. Cow replacement rates are lower, as are associated cow depreciation costs.”

Yet, about 8% of the nation’s cows and heifers exposed to breeding fail to produce a calf each year, due mainly to fertility problems, according to Beef Cow-calf Management Practices in the United States, from the USDA’s National Animal Health Monitoring Service (NAHMS).

More specifically, 93.5% of cows exposed in 2017 calved or were expected to calve. For heifers, the calving percentage was 83%.

In 2018, researchers with the University of Florida Extension service calculated the cost of infertility to U.S. cow-calf producers each year to be $4.7 billion. They also modeled annual losses at the herd level.

For instance, assuming a herd of 100 cows, with annual cow cost of $800, the annual economic loss ranges from $4,000 per year if 4% fail to produce a calf to $10,000 per year at a failure rate of 10%.

Start with heterosis

Harnessing genetics to improve fertility starts with a breeding system that serves operation goals and resources, one that enables taking advantage of heterosis.

Typically, the less heritable a trait – the more the trait is influenced by non-additive genetic effects – the greater the impact of heterosis. Reproductive traits are lowly heritable.

Conversely, the more heritable the trait – the more the trait is influenced by additive genetic effects – the less impact heterosis will have. Carcass traits are highly heritable, while growth traits are moderately heritable.

Consider research from the U.S. Meat Animal Research Center (MARC) at Clay Center, Nebraska. In its research herds, over time, weaning weight per cow exposed is 20% to 25% more for crossbred cows compared to their straight-bred counterparts.

Andersen points out weaning weight per cow exposed measures system level differences in production efficiency because it accounts for failures within the system, such as open cows and calves unable to survive until weaning.

Increased weaning weight per cow exposed for crossbred cows stems from a number of factors, but mostly increased cow longevity. On average and in the same environment, USMARC data indicates crossbred cows last 1.36 more years in the herd and have 0.97 more calves, during their productive lifetime, compared to straight-bred cows. Crossbred cows produce 600 pounds more calf weaning weight during their productive life. The data is from an F1 terminal crossbreeding system where F1 cows are bred to bulls of a breed not represented in the cows.

Retained heterosis varies based on the specific crossbreeding system. Systems can be exceedingly complex or as simple as using F1 bulls or composites.

Focus on bulls next

Commercial producers shouldn’t underestimate the impact of the bulls they choose that pass along genetic differences in fertility to daughters. Think here of expected progeny differences (EPDs) for such traits as heifer pregnancy and stayability.

“Bulls drive herd-level genetic merit for metrics such as pregnancy rate and pounds of calf weaned per cow exposed,” Andersen explains. “Generally, about 85 percent of the genetic change in a commercial cow herd comes from the bulls used during the previous three generations.”

Commercial producers gain added bull selection power with genomic-enhanced EPDs (GEPD), which incorporate individual animal DNA into genetic evaluation. The net result is: Bulls can be selected at younger ages with more prediction accuracy; this is especially beneficial for traits with lower heritability.

If you’re aiming to improve herd reproductive performance and overall productivity via bull selection, Andersen emphasizes using selection indexes that prioritize replacement females and associated maternal traits.

“Effective indexes simplify selection decisions and account for the cost of production (feed) and the quality and the quantity of the output,” he explains.

Then select heifer replacements

After bull selection comes the chance to improve herd reproductive efficiency through replacement heifer selection. Commonly, research studies suggest heifers born earlier in the calving season tend to stick around longer.

In lieu of documenting specific heifer birth dates, Tom Short, director of outcomes research at Zoetis, suggests identifying which heifers were born in the first 20 days of the season, the next 20 and so on.

Traditionally, Andersen says replacement heifer selection has revolved around visual appraisal – looking like a good cow – and when possible, picking early born heifers sired by proven A.I. bulls that are superior for maternal traits. It’s no different at the Andersen family’s Nebraska cow-calf operation.

Unfortunately, Andersen says the visual approach means culling some heifers that should have been retained and vice versa because, historically, genetic predictions for traits such as fertility haven’t been available for commercial replacement heifers.

That’s where genomics can offer added opportunity.

Genomics add to replacement selection

“We are not trying to replace good cowboy common sense,” Andersen says. “The technology is meant to augment time-tested visual appraisal, such that we can evaluate traits in the unseen world that we know relate to the lifetime productivity of a given set of selected females.”

Tests today can provide genetic predictions for a host of individual performance traits in commercial heifers. Predictions are expressed either as a score or as a GEPD, along with the associated animal ranking, relative to a commercial cattle reference population.

These genetic predictions typically come with various economic indexes that combine genetic merit and economics for traits important to profitability.

Different companies predict fertility differently – for instance, providing an estimation of how many more or less calves a female will produce in her lifetime (Fertility) or the likelihood she will conceive and remain in the herd for a particular number of years (Stayability).

Andersen points out the information also enables making better bull buying and mating decisions for individual heifers and cows going forward because genetic strengths and weaknesses across many traits are available for commercial females.

An added benefit of most available genomic tests today is parentage verification. In multisire pastures, that provides opportunity to match calves to individual bulls that have been genomic-tested. It helps track which bulls are contributing the most daughters. It also helps manage inbreeding and future bull selection, Andersen says.

Short points out there are differences between seemingly similar tests from different companies. Reasons include the reference population used to design the test and to calculate subsequent genetic predictions.

When considering a specific genomic test, Short advises asking how accurate the test’s predictions are for the specific breed and type of cattle you want to test.

“Keep in mind, heifers retained bear the total cost of all of the candidates tested,” Short says. “For instance, if it costs 300 dollars to test 10 replacement heifer candidates and you keep five, the cost is 60 dollars per heifer retained.”

“As powerful as genomic tests can be in aiding selection, they cannot replace the foundational elements of planned crossbreeding and bull selection,” Andersen stresses. He points out that after feed and labor costs, cow depreciation often represents the next highest annual cost in commercial cow-calf operations.

“Genomic technology available today gives cow-calf producers easy access to the power of GEPDs and economic selection indexes to make more informed replacement female selection and breeding decisions,” Andersen says. end mark

PHOTO: Photo by Lynn Jaynes.

Wes Ishmael is a freelancer writing on behalf of Zoetis.

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