Expected Progeny Differences help producers determine economical selectionsWritten by Natasha Wheeler
“It is critical to concentrate on traits that are economically relevant to our breeding objective,” notes Matt Spangler, Extension beef genetic specialist at the University of Nebraska–Lincoln.
When managing expected progeny differences (EPDs) in cattle, producers should consider how various traits relate to one another.
“More isn’t necessarily better,” Spangler explains, using milk production as an example.
In a study from the early 1990s, researchers looked at how milk production correlated to the economic efficiency of calves marketed at weaning and harvest.
“Milk production, especially in environments where feed availability is limited, can be a detriment,” he says.
Lactation potential correlates with increased costs for nutritional requirements, Spangler adds, noting that to achieve high milk production, cows require more feed.
“Even when cows are dry, they require more nutrients due to lactation potential because their visceral organ size is larger,” he explains.
Cows that utilize resources for heavy milk production may not do as well maintaining body condition or fertility.
When considering EPD scores, Spangler notes, “Important maternal traits include female fertility, maternal calving ease, maintenance requirements, longevity, maternal weaning weight, disease susceptibility, regional adaptability and temperament.”
Most breed associations maintain scores for all of these traits, except for disease susceptibility and regional adaptation.
“In terminal sire selection, I consider important traits to be calf survival, male fertility, disease susceptibility, calving ease direct, growth rate, feed efficiency, carcass quality and composition,” he adds.
Although EPD scores are generally not yet available for calf survival and disease susceptibility, they are significantly impacted by crossbreeding.
Spangler explains that producers should also consider environmental factors when selecting animals for breeding.
“Phenotype, or the outward appearance of an animal, is really the sum of genetic effects plus environmental factors,” he says.
This means that two animals can reach the same statistics, but in different ways. For example, two calves can reach the same weight at weaning, but not be identical.
“One calf may get there through superior genetics, while the other may get there through an advantage in the environment,” he explains.
This is important to remember when selecting sires, because the visible, physical traits of a bull may not tell the whole story.
“As we choose sires, we have to realize the only advantage the sire passes on to the next generation is through his genetics, not through the environmental benefits he may have been afforded,” he comments.
To learn about which traits are genetic, researchers and producers analyze an animal’s progeny.
“We get an average for a sire’s calves, compared to their contemporaries,” Spangler states.
These data points become the foundation for EPDs, which are then valued by their expected accuracy.
“We shrink EPDs according to our belief in them,” Spangler says. “In a high accuracy sire, EPDs wouldn’t be shrunk much because we have a very high degree of belief in them. A low accuracy sire, where there is considerable uncertainty, will be shrunk more,” he explains.
From there, producers can use scores to determine values such as input traits for their operation.
Spangler illustrates this, saying, “Angus’ dollar energy value on milk and mature size EPDs give producers a feel for which bulls may sire replacement females that may be lower cost.”
Red Angus’ maintenance energy EPD is another example. It focuses on mature weight that is corrected for body condition score, highlighting the maintenance component of milk production.
“These two tools can be used for producers who really need to get a handle on decreasing input costs in a cowherd,” he states.
There are also EPDs that focus on measures of reproduction.
“We know that fertility is at lease twice as economically relevant as either growth or carcass traits,” he comments.
Several breed associations also publish heifer pregnancy and stayability EPDs. Stayability data refers to the reproductive longevity of cows.
Calving ease is also measured.
“There are two types of calving ease – calving ease direct and calving ease maternal,” he continues.
Calving ease direct refers to a sire’s impact on his direct progeny. Calving ease maternal refers to the ease of the calves produced by his daughters.
“It’s important to select for both of those EPDs if producers are retaining replacement heifers,” he adds.
Spangler concludes that selecting for traits should maintain focus on economic relevance to the operation.
“EPDs are seven to nine times more effective for creating change than selecting on actual measurements alone,” he says.
“Unfortunately, EPDs are specific to a breed, and we can not directly compare EPDs of different breeds against each other,” comments University of Nebraska-Lincoln Extension Specialist Matt Spangler.
To compare across breeds, producers can find across-breed adjustment factors, which are published annually by the U.S. Meat Animal Research Center (MARC).
“These can be used to adjust EPDs so we can get a fair comparison across breeds,” he notes.