Genetic improvement can be complicated, here’s a look at the basics
“Why do we need genetic evaluation? This is a basic question,” Dr. Natalie Leite admitted to the crowd attending the American Wagyu Association’s Annual Convention in Charlotte, N.C, held Sept. 22-24. “And, the answer is just as basic – we want to be concerned about selecting the best animals to compose the next generation in our herds.”
From here, however, things begin to go from basic to complicated.
There’s genetics and genetic variation within a breed and then there’s the environment the cattle live in, which can affect how animals’ genetics are expressed.
During the convention, Leite discussed the basics for genetic selection.
Selecting traits and analyzing EPDs
First, it’s important to decide what traits are important. Then, analyze expected progeny differences (EPDs) for the traits a producer wants to improve or emphasize in their herd. EPDs have been the standard bearer in genetic improvement for around 50 years, she noted.
“EPDs are basically the value, on average, we expect the progeny of a certain sire will perform in relation to other sires in the same evaluation,” Leite said.
This means, within a breed’s sire evaluation report, a person can compare the potential for sires on various genetic traits. However, Leite cautioned Wagyu breeders against comparing EPDs from sires of different breeds or sires not included in the same evaluation.
Leite demonstrated how EPDs work with a basic example looking at weaning weight. She took a hypothetical Bull A with an EPD of 70 and Bull B with an EPD of 60.
“So, the difference between these two sires is 10 pounds. What is the translation of this?” she asked.
The 10-pound difference in the EPDs means one can expect the progeny of Bull A will perform 10 pounds better on average compared to Bull B.
Leite continued, “Keep in mind, however, when we talk about EPDs, we are talking about what is ‘expected.’ When we expect something, we are not certain about it. Just because there’s a 10-pound difference between the two bulls in their EPDs doesn’t mean every calf from Bull A will weigh 10 pounds more at weaning than every calf from Bull B.”
Enter accuracies. The more progeny data a bull has adds to the accuracy of the EPD. So, a young bull in a bull stud will have low accuracies while a bull which has been around for a while and has lots of progeny data reported to the breed association will have higher accuracies.
“This is important because different genetic traits have different levels of heritability,” Leite shared.
Heritability of a trait is expressed in decimals between zero and one. So, a moderately heritable trait will be expressed as 0.3 or 0.4. However, she reminded Wagyu breeders, it’s important to remember genes for a particular trait don’t exist in a vacuum.
“Something very interesting about genetics is genetic correlation. All the time we spend to make a difference in improving a trait, there is a high chance we are also making changes in other traits,” she said.
For example, if a producer is selecting for heavier weaning and yearling weights, it’s possible birth weights will increase as well. This is where selection indexes come to the fore.
Evaluating a selection index
“A selection index will assure a producer they’re not selecting the best animals for a certain trait but at the same time have a negative EPD on other traits,” Leite said.
The selection index will indicate which animals are more genetically balanced and those are the animals producers should be interested in the long term.
Now consider genomics or what the deoxyribonucleic acid (DNA) analysis can discern about an animal’s genetic potential.
“Within the same species, we share 99 percent of our genetic material,” Leite told Wagyu breeders. “But then there is one percent of the genetic material within a breed that’s different.”
This one percent can be millions of individual genes.
The points on the DNA helix where animals can differ are called markers. For example, a calf will share 50 percent of its DNA with the sire, but the 50 percent calf number one shares with the sire is not the same 50 percent of calf number two. And, we have markers to follow this.
Assume a producer wants to select for marbling and has several promising young bulls. A DNA analysis will show whether those young sires are more predisposed to sire calves with good marbling based on the markers for the particular trait.
The advantage is genomic information will increase the accuracy of the EPD for young sires, and as genetic accuracy increases, generation interval decreases.
“We can select animals at a much younger age because we have high accuracies. So, we increase genetic gain when we have genomic information,” Leite concluded.
Burt Rutherford is the director of content and senior editor of BEEF Magazine. Rutherford can be reached at email@example.com.