November 8, 2022
Some cattlemen take advantage of heterosis (hybrid vigor), with crossbreeding or composites. Research in the early 1900’s demonstrated the benefits, including breed complementation (combining desired traits from 2 or more breeds, to gain characteristics lacking in one of the parent breeds).
By careful crossbreeding you can add traits from a different breed, and overcome some of the weaknesses of each breed. The crossbred animal also benefits from heterosis—the performance advantage that enables the crossbred to exceed expectations of the parent breeds.
Reynold Bergen, science director, Beef Cattle Research Council (Calgary, Alberta), says hybrid vigor is the degree to which progeny outperform the average of the two parents. “In other words, if breed A averages 100 and breed 2 averages 110 for a certain trait, the expected calf’s performance would be the average between the two, which is 105. But if the calf’s performance is actually 112, it outperformed the parental average, which is what hybrid vigor does,” he says.
Heterosis beneficially influences many traits important for beef production, including those that are hard to select for, such as fertility, reproduction, strong immune function, calf survival (hardier calves), and longevity. “Those traits depend on combinations of genes. They are not a stack of genes (like we can create with selective breeding in purebreds); they are more like a web of genes,” Bergen explains. When you keep narrowing the gene pool and stacking certain genes, you lose some combinations and start to see negative effects.
“So to improve those traits and strengthen that web we add more variation—by crossbreeding. This produces the best of both worlds. The highly-heritable stacked traits from one breed work fine with the stacked traits from the other breed, but the different combinations will add back the fertility, longevity, immunity etc.”
Heterosis is maximized when breeding animals with very different genetics, completely unrelated—such as a British breed and a breed containing Bos indicus (zebu), like Brahman. Heterosis is also great when crossing British breeds with continental breeds, though all these animals are Bos taurus. British breeds are less closely related to most continental breeds than to each other (or continental breeds to one another).
Mating animals within the same breed limits genetic potential to some degree because all modern breeds were created with a certain amount of inbreeding to “fix” the desired characteristics, for uniformity in the offspring. A certain amount of production potential is sacrificed to gain the uniformity, since the most dependable way to gain uniformity is by using inbreeding and linebreeding. A breed is a closed group (not allowing infusion of other genetics) and accumulates inbreeding over time, even if it’s not done deliberately.
Crossbreeding is the opposite of inbreeding. As explained by Dr. Jim Gosey (retired University of Nebraska Extension Beef Specialist), heterosis is the recovery of accumulated inbreeding depression. In one generation, offspring exhibit the maximum of what was lost through generations of “pure” breeding. Heterosis is maximized with a 3-breed crossing system, mating a crossbred cow with a bull of a third breed.
Composites are popular because they simplify the breeding program; the animals are already mixed in a desired combination. The breed “mix” is the same in sire and dam and has been standardized into a predictable blend over several generations of breeding crossbred to crossbred. The animals are all the same percentage of certain breeds, such as half and half of two breeds, or 3/8 of one breed and 5/8 of another, or a certain blend of 3 or more breeds. Brangus (Angus and Brahman), Santa Gertrudis (Shorthorn and Brahman) and Beefmaster (Brahman, Shorthorn and Hereford) were some of the first composites.
Using a composite bull on composite cows eliminates need for separate breeding pastures or rotating breeds of sire. If the breeds complement one another, and the composite was created with careful selective breeding and enough genetic potential to avoid inbreeding, calves are uniform and consistent.
There’s not as much heterosis as in F1 crosses, but still a significant gain over straightbred cattle. A composite utilizing 2 breeds that contribute equally to the mix will consistently deliver 50% heterosis. When 4 breeds are used equally for the composite, heterosis is 75%, in each generation, continuing over time. The initial loss of heterosis in any crossbreeding program occurs between the F1 and F2 generations, but with a composite the remaining heterosis is maintained in subsequent generations. How much is maintained depends on how many breeds are in the initial mix.
As pointed out by Michael MacNeil (research geneticist at the USDA Agricultural Research Service at Miles City, Montana, in 1998) a composite doesn’t need equal genetic contribution from the breeds involved. If one breed is better in certain desired traits, it can be represented more extensively in the mix. One composite developed at the Fort Keogh Livestock and Range Research center is 50% Red Angus, 25% Charolais and 25% Tarentaise. With this combination, heterosis is about 63% in each generation.
The heterosis in a composite is retained indefinitely unless these crossbreds are inbred again. This can happen if the composite was formed by using just a few bulls from each contributing breed. Animal scientists recommend the mix be based on at least 15 to 20 sires from each breed. Once the composite has been established (all animals are a certain percentage of each parent breed, the vigor of the composite can be maintained by using at least 25 bulls per generation, to keep the rate of inbreeding low.
Easier with a large herd
It’s easier to create a viable composite using thousands of animals than for a rancher with a small number of cattle to create his/her own composite. To do that, infusions of “new” genetics (unrelated crossbred bulls) must be added to the mix now and then. Some ranchers use this “open” composite approach, continually selecting new sires (purebred or crossbred) or using AI, choosing new bulls and sometimes new breeds. Then much of the heterosis is on-going in each generation.
Combining several breeds that complement one another enables stockmen to match the cow herd more perfectly to various conditions and/or produce the type of calves that best meet a target market. For instance, many ranchers feel that a mix of British and continental genetics comes closer to meeting some market requirements than either can do alone.
Utilizing composites or crossbred bulls is often more beneficial than using a terminal cross to create beef calves for market and having to buy replacement heifers and have the genetic fate of your operation is in someone else’s hands. Many stockmen prefer to be able to retain some of their best heifers as cows, and most composite blends enable them to do this.
Some stockmen are still wary about composites, thinking that genetic variation (expressed as non-uniformity in the calves) would be greater than in a purebred herd. But Gosey points out that a study of 3 composite blends and their parent breeds (at USDA’s Meat Animal Research Center in Clay Center, Nebraska) found that the herds of composites had as much uniformity in the end product as the purebreds.
And in one group of composites developed by the University of Nebraska, in which foundation bulls were better than average in calving ease and milk production, and average or below in mature size, and above average in marbling and other carcass traits, the steers from this composite averaged 87% USDA Choice or better, and 66% yield grade 1 and 2, which meets the beef industry’s goals for finished cattle. Composites can provide a practical way to enhance management efficiency and increase profitability.
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