Heterosis Factor

By Becky Mills
Progressive Farmer Contributing Editor

When it comes to bulls, what seems like a good idea at weaning doesn't always look so good a few months down the road.

Take Will and Monnie Carol Carter's Angus-Simmental crosses, for example. Their two-way rotational cross meant they had a second-generation calf crop that was a mix of both three-quarter Simmental calves and three-quarter Angus calves.

"They looked uniform at weaning, but then they really separated," Will said of the calf crop. "We were getting a lot of up and down."

The Hope Hull, Ala., husband and wife team made the move to SimAngus bulls, with a goal of producing more uniform steers and heifers from their 200-head cow herd. This helped them attain a smaller-framed female, which was not as challenging to hold body condition on as the higher-percentage Simmental cows.

SimAngus bulls are a composite breed that can be five-eighths Angus and three-eighths Simmental; three-quarters Angus and one-quarter Simmental; or one-half Angus and one-half Simmental. The Carters use the half-and-half combination.

"We like the simplicity of crossbreeding with a composite," Will said, adding they still get the benefit of hybrid vigor.

Hybrid vigor, commonly called heterosis, is the boost in performance that results from crossbreeding. Normally, the performance of the offspring is greater than the average performance of the two parents.

The greatest amount of heterosis, 100%, comes in that first cross, known as the F1. In a two-breed rotational cross (like the Carters initially had with their Simmental and Angus bulls), heterosis drops to around 66%. By using a composite made up of the same breeds as their cow herd, Auburn University animal scientist Lisa Kriese-Anderson said it probably drops even more, to around 50% to 55%.

"That is still more efficient than having a commercial herd of one breed," she noted. "It is more like having a purebred operation with two different breeds when it comes to extra pounds at weaning."

Will added theirs is a simple breeding system, which is important for the couple. Both are veterinarians with their own practice, which leaves cow chores for nights and weekends. Plus, they have two small children.

THE BRANGUS BUMP

Moving to the SimAngus bulls was a step forward, but the Carters still weren't satisfied with their crossbreeding system. While calves were more uniform and had more Angus influence, they weren't seeing enough pounds of calf coming across the scales.

"We needed more growth," Will said. "We worked hard to get them to 720 pounds by the time they were shipped." This was after weaning the calves and giving them a 45- to 60-day preconditioning period.

The Carters decided to add another breed to their program -- Brangus. Made up of five-eighths Angus and three-eighths Brahman, the Brangus has had its own breed association since 1949. The results were impressive.

"We added 100 pounds to our weaning weights the first year," Will said. "That was just from using Brangus sires. Now those calves are 825 pounds at shipping. We didn't change anything else. Heterosis is responsible for that increase in weaning weights."

While another breed or composite could possibly have provided the same jump in sale weights, Mark Thallman, research geneticist at the U.S. Meat Animal Research Center (USMARC), said the extra pounds could be due to breed- specific heterosis from the Brahman influence in the Brangus sires.

"The breed-specific heterosis when a Bos indicus (Brahman) animal is bred to a Bos taurus (English or Continental) animal is considerably greater than when a Bos taurus is bred to a Bos taurus," he explained.

How much greater hasn't really been proven. The Clay Center, Neb., researcher said one of the objectives of the Germplasm Evaluation Project currently underway at USMARC is to estimate breed-specific heterosis. It is expected to take five to 10 years before the project possibly provides any concrete answers.

The Carters' cow herd is an example of another advantage that comes with crossbreeding, whether it is with purebreds or composites. That advantage is known in the industry as complementarity. Essentially, it means each of the breeds brings different traits to the table, breed complementarity.

Billy Moss, a SimAngus breeder from McCormick, S.C., said Angus and Simmental complement each other well. Angus provide maternal traits, they are easy fleshing and high marbling. Simmentals provide growth, muscle and milking ability.

The infusion of Brahman blood from Brangus sires provided adaptability to hot and humid climates for the Carters. As an added bonus, Brahman crosses have a reputation for longevity. Their replacement heifers are now products of SimAngus bulls bred to their predominantly Brangus cows, and Brangus bulls bred to their predominantly SimAngus females. Will Carter described them as moderate-framed and easy-fleshing.

"For years, we bought replacement heifers, but after we started getting our bull genetics like we wanted them, we can produce better replacement heifers than we can buy," Monnie Carol said.

Conception rates attest to how good these replacements are. The operation has a 90-day breeding season, and conception rates are 95% -- a 5% increase since they brought in the Brangus influence.

Will said they had a 30% fallout rate with purchased replacement heifers. With their own heifers, they have a 10% fallout rate. Culls are usually selected for one of three reasons -- they're open, they have a bad disposition or they lack fleshing ability.

While it might seem logical that a composite breed or breeds could contribute to a lack of uniformity in the cow herd, that doesn't have to be the case.

"Uniformity is a function of selection," said Kris Ringwall, director of the Dickinson Research Extension Center, Dickinson, N.D. "When you cross two breeds, the F1 cross is quite uniform. But when you use crossbred bulls on crossbred females, uniformity goes backward. This is offset by selection pressure and the use of data."

Auburn's Kriese-Anderson added that using a composite bull is just like using a purebred bull. If you don't have a planned breeding program and stick to it, you'll end up with a whole herd of mishmash cattle.

(VM/CZ)

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