There’s plenty of breeding terminology out there that as part of your tool box you can sound like you know a thing or two but be careful when it comes to the Antagonist Traits, as it’s a bit more complex to understand. However, with a little bit of knowledge, you will be head and shoulders above the rest and can add that to your tool box with confidence.
It also helps explain why marbling has been so hard to bring into herds because it has largely been an antagonistic trait to some of the other key commercially valuable traits that we have traditionally selected for.
An antagonist trait or a negatively correlated trait is one that is linked to another trait inversely. One goes up, the other goes down. Unfavourable genetic correlations are sometimes referred to as genetic antagonisms. Genetic antagonisms cause decreases in genetic merit for some traits when single-trait selection is practiced or when failing to consider selection responses in correlated traits that are not directly under selection.
An obvious genetic antagonism is birth weight and calving ease, as birth weight goes up, calving ease goes down. Another less obvious one is Direct Calving Ease and Calving Ease Daughters. Direct calving ease is heightened by using a bull with essentially lower growth, which can sacrifice the growth potential of his daughters, meaning when they are at calving age may not have enough skeletal frame to maintain the calving ease of the herd. That is why we recommend that as a rule progeny from a heifer bull are not kept as replacements. We all like the curve benders that break these rules, those bulls that have inherent calving ease but solid growth out the other side.
Another relevant antagonistic trait is front claw to growth. As we select for higher growth bulls, so do the claws grow faster and if the leg structure is not adequately correct, the rate of growth of the claw is more than the rate of wear and the result is extended claws and lameness. This is a game of risk and reward, where the stud breeder looks to push the envelope in a performance direction but may inadvertently have to deal with a higher degree of culling to sale day if the wrong bull is used.
Another common antagonistic trait is mature cow weight to growth. As we select for growth, there is a tendency for mature cow weight in the herd to increase, unless you look for bulls where the mature cow weight ebv is less than the 600 day growth ebv. However, selecting bulls with mature cow weight too low can lead to another antagonism of an increase in calving difficulty.
Now on to marbling. There is a reason not all herds (stud and commercial) have chased this trait. It’s a very frustratingly antagonistic trait. If anyone knows Wagyu they will attest to this, yes…they marble but it takes an extra year to finish them. Amongst others, marbling is antagonistic to Eye Muscle Area and Yearling Growth (Koots et all, 1994), or if you like, growth and carcass in general. Over the years there have been curve bending bulls that have broken this antagonism but these bulls have only come to light through the efforts of those that have selected for both traits and measured for marbling. These bulls have grown, had carcass weight and marbled.
It’s taken us time to start to get consistent marbling across our sales and it’s still a work in progress. Commercial breeders have to make the same choice as we did, to either stay traditional or to chase high value carcass traits that now can add up to a dollar per kg premium (potentially over $10K for a unit of cattle – it’s been done now!) or make your store stock very sort after (if they are identifiable – use the Angus Pure tags!).
To get IMF into your herd, you’ve got to do it in a way that doesn’t compromise your other commercially valuable traits, such as growth. Look at your bulls and work out what their average IMF ebv is. To lift that you will have to use bulls with an IMF ebv of at least 2 above what you have been using, easier said than done considering only half the genetic lift comes from the male. The bulls we have put into the 2 year old sale have ideally been selected to have good IMF but also above breed average for growth. Also look at using Heifer Select, a genomics tool through Zoetis, to measure IMF potential in your replacements.
Source of some of this interesting stuff – SELECTING FOR CARCASS MARBLING AND MUSCLING BENEFITS AND PITFALLS, Jim Gosey Extension Beef Cattle Specialist Animal Science Department University of Nebraska, Lincoln.