Dr. Troy Rowan, assistant professor, beef cattle genomics, University of Tennessee, realizes cattlemen may not see the value of genomic testing for commercial heifers, but he offers solid information on why it’s worthwhile.

“Traditional heifer selection strategy has been to buy good bulls, use common sense and hope for the best,” said Rowan. “We didn’t have any way previously, aside from knowing sire EPDs or cow family history, of knowing the actual genetic potential of heifers we’re investing in and retaining.”

Despite genomic advances, phenotypic (physical appearance) selection criteria play an important role in heifer selection. “Age is probably the most used,” said Rowan. “Older heifers will start cycling faster and are more likely to get bred at the first opportunity. They have a longer anestrus period after the first calf and are more likely to rebreed with the second calf. We know it’s difficult to get animals cycling again after the first calf, so older animals do better.”

Other phenotypic heifer retention metrics include pelvic scores, dam performance (keeping good heifers out of good cows), heavier heifers (weaning weights) and confirmed pregnancies.

Rowan explained the role of genomics in replacement heifer selection: “We have to draw lines about what genomics does and doesn’t do. Genomics helps us estimate genetic merit on traits and help us increase EPD accuracy of unproven animals. For commercial heifers, it gives us an EPD to start with. We have a prediction of an animal’s genetic potential rather than other more conventional, pure phenotypic measurements.”

Genomic information can accelerate genetic gain to move a population ahead. However, genomics can’t perfectly predict phenotype for individual animals. Rowan said it’s important to understand that while genomic tests provide genetic insight, they can’t account for non-heritable or non-additive traits. Genomic testing doesn’t provide a pure phenotypic prediction for an animal but can provide an idea of her genetic potential.

Cow longevity is one of the most important female selection traits. “An enormous chunk of the commercial cowherd’s profitability goes into the long-lived cow,” said Rowan. “If a cow lives past the pay-back period, we don’t have to replace her. She lives longer in a profitable stage.”

However, the heritability of longevity is quite low – 0.1 might be “generous,” said Rowan.

“Only 10% of this trait is due to genetics, the other 90% is due to the animal’s environment and how it was managed as a calf and developing heifer. It isn’t just fertility – it’s udder, feet and legs and other traits.”

The reliability of a genomic EPD is 0.5. “That tells me a genomic test score explains only about 5% of the longevity differences in a heifer crop,” said Rowan. “The genetic component is all these tests can tell us. But it’s still valuable. It isn’t guaranteeing anything – if I select a heifer that’s in the 99th percentile for a trait like longevity, that only explains a small chunk of the differences in the animal’s phenotype. It’s important we continue to use genomics alongside common-sense predictors such as age, weight and body condition at breeding. Genomics shouldn’t be the silver bullet but it’s a useful tool alongside other common-sense predictors.”

For commercial cattlemen, Rowan suggests genetic evaluation similar to the way in which a purebred animal would be tested. “We can also use marker effects which look at all 50,000 DNA markers and determine how much of each version of the marker contributes to a phenotype of interest, adding them up across the genome and reporting back a single number that reflects the animal’s genetic potential,” he said, adding that rather than thinking about phenotypic predictions on individual animals, consider predictions as a tool that helps improve the population faster.

“One of the things to keep in mind about genomic tests is that seedstock animals are the major driver of genetic trends in the commercial cow/calf sector,” said Rowan. “The rate of genetic gain across generations of selection is determined by the seedstock individuals we’re pulling in. There’s a boost in the first-generation selection of replacement females, but the big driver of genetic change over time is from the seedstock population.”

Producers who genomically test commercial heifers should test more heifers than they plan to keep. “If we are only testing heifers we’ve already decided to keep, we’re throwing $35 down the drain,” said Rowan. “We need to test the top two-thirds of heifers and use that information to make decisions. Testing more heifers than we plan to keep is imperative, otherwise it’s expensive confirmation bias.”

Rowan described three valuable considerations for making commercial heifer replacement decisions. “First, identify animals with the highest heterosis potential,” he said. “Replacement female traits such as fertility and health are lowly heritable, and we know heterosis plays an outsized role. Cow longevity is 0.1 heritability, but the heterosis we expect in a crossbred female is around 25%. I like to use genomic tests to identify which heifers are the most heterozygous. They have the most potential for expressing heterosis in replacement female traits we’re interested in.”

Second, genomics can help breeders make more precise mating choices, starting with bull selection. “Getting the bull decision right is so important,” said Rowan. “Even on an individual heifer level, if we’re using AI, we can make strategic mating decisions between animals when we understand the strong and weak points of a heifer.”

Genomic information allows the producer to select bulls that improve heifer weaknesses, add value to offspring and ultimately make faster progress with herd improvement.

The third consideration is emerging new genetic programs that will help cattlemen use genomics to add value to feeder calves.

“We can sell our feeder calves based on the potential they have genetically before they’ve had an opportunity to express it, especially regarding post-weaning gain and carcass merit,” said Rowan. “People who purchase cattle are interested in having more information, and programs are emerging that allow us to capture some of that value from genomic testing.”