FEATURE ARTICLE
BREEDING A BETTERADAPTED COW by Troy Rowan, Ph.D., University of Tennessee, assistant professor and extension beef specialist We have all heard stories of that high-dollar cow that our neighbor brought in from Montana, only to have her melt when the temperatures cracked 90˚F or the fescue got especially hot. We know that some cows are better suited to challenging environments than others. Many estimates show that the economic and performance impact of this maladaptation is substantial, costing the industry billions of dollars per year. While these anecdotes abound, digging into the genetics that governs adaptability and turning them into useful selection tools presents a complex challenge. As the climate becomes more volatile, breeding cattle that can
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November 2021
excel in their environment will be of the utmost importance. Moving forward, we can take two different paths to address animal adaptability with genetic tools: selecting for adaptive novel phenotypes or changing how we perform genetic evaluations. NOVEL PHENOTYPES FOR ADAPTATION The first path to breeding more adapted cattle is using phenotypes that indicate how they handle environmental stressors. Two adaptive phenotypes, early-season hair shedding and pulmonary arterial pressure (PAP), are being widely measured across the industry. PAP is a measurement of an animal’s blood pressure and serves as an indicator for the likelihood of experiencing high altitude disease. At the same time, early-season hair shedding is an indicator of an animal’s adaptation to heat. To evaluate early-season hair shedding, we use a visual 1-5 score to measure how much of a cow’s winter coat remains. This phenotype is typically scored between late April and June, depending on when variation in shedding is highest within a herd. Researchers from the University of Missouri undertook a major initiative to aggregate thousands of hair scores from most of the major beef breeds in the U.S., including Brangus. While hair shedding is not an economically relevant trait in itself, its impact on a cow’s ability to respond to heat stress or toxic fescue stress directly impacts her productivity. The difference in weaned calf weight between cows with hair scores of 1 (completely slick) and 5 (full winter coat) ranged from 35 and 50 pounds depending on the breed. When cows don’t have to devote energy to regulate their body temperature, they can spend more energy raising their calf. As with any phenotype, with enough records in a genetic evaluation, we can generate EPDs to increase the selection accuracy of these adaptability traits. Traits must be sufficiently easy to measure to build large enough datasets to calculate EPDs. While selecting solely on a cow’s hair shedding or PAP score probably isn’t advisable, it may serve as a “tiebreaker” in some culling or selection decisions. In the future, we might anticipate selection indexes that use traditional performance
