Cattlemens News Heterosis

by Troy Rowan, Assistant Professor and Extension Specialist (Beef Genetics)

As producers, we should always be striving to make the most profitable decisions for our herd. While I’m not an economist, I have a pretty good handle on the two pieces that make up profitability: Revenue and costs. When it comes to genetic selection, I think we have historically done a great job of selecting for traits that increase our revenue like having a live calf and weaning weight. However, when it comes to the “cost” traits, especially those that deal with cow efficiency, selection can be less straightforward. Long-lived cows are the cornerstone of a profitable commercial cowherd. Making these efficient, fertile, sound, and productive females is paramount for a commercial herd to be profitable.

There are precious few “can’t lose” propositions in the world, especially when it comes to our bottom line in the cattle business. Crossbreeding is one of those actions that a commercial herd simply can’t afford to skip. The advantage that crossbred animals experience from heterosis, or hybrid vigor, affects all of the traits that we know drive profitability: from weaned calf pounds to cow fertility and longevity. If we’re not taking advantage of crossbreeding and heterosis, we’re leaving dollars on the table! The benefits of crossbreeding are twofold. First, it allows us to take advantage of breed complementarity. This means that we can match the strengths of different breeds, stacking favorable traits to get the best of both worlds in our crosses. This might mean crossing a strong maternal Angus/ Hereford female with a leangrowth Charolais or Limousin sire. It could also mean using a Bos indicus-influenced breed on a British-based commercial cowherd to add some tolerance to heat and/or fescue stress in certain regions of the country. The other major benefit of crossbreeding is heterosis or hybrid vigor. When we breed two animals of the same breed, we’d expect that the offspring’s performance would lie around the average of the two parents. We call this the “midparent” value. Heterosis is the overperformance of crossbred offspring when compared to the average performance of the two parent lines. When we crossbreed animals, we see boosts in performance across traits. The amount of heterosis that a crossbred animal experiences depends on two things: How different the parental breeds are, and how heritable a particular trait is. The more distantly related two breeds are, the more heterosis we would expect to see from their crossbred offspring. continued on page 13

For example, we wouldn’t expect to see a huge amount of heterosis when we cross a Red Angus and a Black Angus. These two breeds split only about 70 years ago, providing them only a short amount of time to collect genetic differences. However, crossing an Angus and a Brahman, two entirely different sub-species of cattle, would generate a huge amount of heterosis (Bos indicus and Bos taurus populations split about 250,000 years ago). It’s important to keep this in mind when we are selecting bulls for our crossbreeding program.

For example, if our cowherd is Angus-based, a SimAngus bull will generate less heterosis than a purebred Simmental bull on the same cows.

The amount of heterosis is also dependent on how much genetics controls a trait. The heritability of a trait (i.e., how much of the trait is controlled by genetics versus environment) has an opposing relationship with heterosis. Traits where genetics play a smaller role experience larger effects from heterosis. This is especially important when it comes to cow-focused traits like fertility, longevity, and health. These traits all tend to be lowly heritable (0.1-0.2), but they can experience boosts upwards of 20-30% due to heterosis. The advantage in fertility, longevity, and health that crossbred females provide is something that commercial cow-calf operations can’t afford not to take advantage of. Crossbreeding could mean an extra 20% of crossbred heifers getting pregnant or an extra calf throughout a crossbred cow’s lifetime. Crossbred females are the cornerstones of a profitable commercial cowherd. They are productive longer, stay healthier, and breed back quicker.

While heterosis plays a more prominent role in lowly heritable traits, it also affects other traits. For the moderately heritable traits that we rely on to generate revenue, like weaning weight, the crossbred advantage can be around 5-10%. This is free money that we’re leaving on the table when we aren’t crossbreeding!

I’m all for easy solutions to complex problems, and when it comes to breeding cattle, there is not a more universally advantageous solution to increasing the profitability and productivity of a commercial cowherd than crossbreeding.