Agricultural News: Cattle Genomics

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Cattle Genomics: Heterosis boosts the bottom line
Dr. Troy Rowan, Assistant Professor

UTIA Genomics Center for the Advancement of Agriculture
Sometimes, I get ahead of myself as a beef cattle genomics researcher. I’m always thinking about the “next big thing”, or the next major step forward in the genetics and genomics space. While those occasionally happen (for example, the development of EPDs in the 1970s or genomic-enhanced EPDs in the 2010s), there are typically a host of the “little things” that we can do in our operation on the genetics side, that when done together make a big impact on a herd’s profitability. When I’m asked what genetic strategy or technology would generate the greatest influx of profit into the beef industry, my answer isn’t the shiniest new genomic test or even the universal adoption of EPDs. It’s more crossbreeding. Geneticists have long known that when we breed two divergent lines with one another, the progeny often outperform the average of their parent’s phenotypes. The biological cause of this phenomenon, heterosis, has not been completely nailed down. Despite the unclear underlying biology, one fact is clear: It works! Crossbreeding, when used in conjunction with well-defined breeding goals, has the potential to improve every economically-relevant trait in your herd.

According to a 2008 USDA report, only 45% of commercial cowherds were utilizing any form of crossbreeding, a number that has likely dropped in the years since. It is always surprising to me that so many commercial producers leave money on the table by not leveraging crossbreeding in their operations. While other management interventions harbor additional costs to implement, the gains realized from crossbreeding are effectively pure profit!

Heritability, or the proportion of variation in a trait that is attributable to genetics, varies between traits (for example, see https://www.angus.org/Nce/Heritabilities.aspx). For a given trait, the increase in crossbred progeny performance compared to the average of its purebred parents’ performance (heterosis) is inversely related to heritability. This means that for high heritability traits like carcass quality, heterotic gains are typically small (0%-5%). Crossbred calves have been shown to have weaning and yearling weights ~4% higher than their parent’s average (Cundiff and Gregory, 1999). While this may seem modest, my cowboy math suggests that implementing crossbreeding could add another $30-$50 per head in weaned calf weight. Multiply this across an entire herd and suddenly we are talking about significant gains to our bottom line. For lowly-heritable traits like fertility, cow longevity, and health, crossbred animals can experience heterotic gains in excess of less than 25% compared to their parent average. Cundiff and Gregory (1999) estimated that a crossbred cow would produce on average one more calf and wean off at least 600 more pounds of calf weight compared to a purebred counterpart over the course of their lifetimes. These effects of heterosis make multi-generational crossbreeding an attractive way to capture not only the individual performance gains of an F1 calf but even greater returns from maternal heterosis in replacement females.

As with any decision on the farm, we are always best served by approaching crossbreeding decisions with a plan in mind. Simply turning out a different breed of bull doesn’t guarantee that you’ll observe any performance or economic gain. Not every cross actually makes sense. An F1 Angus x Miniature Hereford calf will likely outperform its parental average for weaning weight, but it won’t outperform a straight bred Angus calf. When crossbreeding, matching complimentary breeds with one another is a great way to both exploit heterosis and the additive differences that exist between breeds (i.e. Charolais growth + Angus marbling & calving ease). Gains due to heterosis will also be greater in crosses between more divergent breeds. An Angus x Red Angus (two closely related breeds) cross will have substantially lower heterosis compared with an Angus x Brahman cross (two different subspecies).

Introducing crossbreeding to your herd can be as simple or complex as necessary. We often think about heterosis in the context of producing terminal F1 animals. While individual heterosis is maximized in the F1, it is possible to retain heterosis for multiple generations through the use of rotational crossbreeding systems or advanced generation crosses. Complex rotational crossbreeding systems with more breeds will require a more hands-on approach and logistical planning but result in greater retained heterosis for both individual and maternal traits. A more detailed look at crossbreeding plans and programs can be found in this eBeef factsheet: https://beef-cattle.extension.org/crossbreeding-for-the-commercial-beef-producer/.

An easier way to exploit heterosis in your herd outside of a defined crossbreeding plan can be achieved through the use of composite females and a regularly rotating set of bulls. Composite females have long been popular in some commercial herds as a way to leverage heterosis in maternal traits. Further, Bos taurus x Bos indicus composite females have long been popular in heat-stressed environments. Recently, many major breed associations have opened their herd books to composite animals (i.e., the American Simmental Association and International Genetic Solutions). In doing so, they have enabled multi-breed genetic evaluations that make it possible to calculate accurate EPDs on crossbred animals. These more accurate selection tools make using crossbred bulls (SimAngus, LimFlex, Balancer, etc.) a practical approach to introducing further heterosis into herds.

While we as researchers are still trying to understand the exact biological basis of heterosis, the gains resulting from crossbreeding are undeniable. By combining breed complementary and heterosis, producers can increase the performance of their calf crop and replacement females for virtually every economically relevant phenotype.

Article originally submitted on UT’s Beef & Forage website. Article courtesy of UTIA.