Stay-ability marks an important measure of cowherd efficiency
Lincoln, Neb. – “I could ask anyone what their definition of efficiency includes, and each one would probably be different,” said Scott Speidel of Colorado State University. “We have challenges out there, and breed associations are using different ways to measure efficiency.”
In a presentation at the 2014 Beef Improvement Federation Research Symposium and Annual Meeting June 18-20, Speidel noted that cowherd stay-ability is an important efficiency factor.
Speidel defined stay-ability as the probability of a cow surviving to a specific age, provided they have been given the opportunity to reach that age.
“High stay-ability cows remain in production long enough to generate enough revenue to offset their costs,” he continued. “Evaluations found that breakeven on these cows is about six years of age. We need five calves to generate enough revenue to offset the cost of production.”
Those animals that fall out of the herd earlier are costly, and a lot of the fall-out, Speidel said, occurs prior to three years of age.
“We need a tool to select for those cows that get past that age,” he commented. “We are not talking necessarily about longevity. We are talking about reproductive efficiency.”
In addition to living a long life in the herd, Speidel remarked that cows must produce a calf every year in the same season.
“Stay-ability accounts for 53 to 67 percent of the value of most maternal indexes,” he said. “That is a huge number when we think about economic efficiency.”
In determining an expected progeny difference (EPD) formula, Speidel noted that several considerations must be made.
Useful EPDs also require that the data is collectable and can be evaluated appropriately. Additionally, traits must be heritable, show variation across the breed and be economically relevant.
In determining stay-ability, Speidel noted that useable data is necessary.
“If we are going to have an EPD with any sort of accuracy, we need to collect data relatively easily, simply and cheaply to use that in our evaluation,” he commented.
Evaluating stay-ability requires easy data collection.
“We look at whether or not they have been in the herd to six years of age,” Speidel commented. “It is really easy to collect data. We send it in to our breed associations every year.”
For example, the Red Angus Association (RAA) evaluates stay-ability and has for the last 20 years or so. RAA requires that the cow has a calf in consecutive years without changing season.
Additionally, contemporary groupings are also considered in evaluating stay-ability.
“We look at the breeder of the cow or calf,” said Speidel. “The observation for contemporary grouping is either a zero or a one – either they stayed in the herd or they didn’t.”
However, with evaluating stay-ability for accuracy, Speidel noticed a challenge. By the time stay-ability, can be accurately determined, cows are nearing the end of their productivity and bulls are either dead or their semen has been frozen.
“Accuracy directly affects the genetic programs,” he said. “If we can increase accuracy, we should be able to increase the rate of genetic progress.”
To increase accuracy, correlated traits – such as carcass traits, weaning weight and birth weight – are utilized. Additionally, they look at the same traits measured at earlier ages.
“We know stay-ability is heritable of six years of age, but what about stay-ability at only three years old?” he asked.
In studies, Speidel noted that 64 percent of the genes associated with stay-ability at three years of age are the same genes associated with stay-ability at six years of age. An 88 percent correlation exists between the trait at five and six years of age.
Other data suggests that correlated bull traits – such as scrotal circumference and 420-day weight – may also have a correlation, though there is limited research on the subject.
Accounting for heterosis
An additional challenge for those commercial breeders using crossbred cattle is accounting for heterosis in looking at stay-ability of the cowherd.
“In a typical evaluation, we don’t include data on crossbred animals,” Speidel said. “If we just look at the breeding values, crossbred animals will appear better than purebred because of the genetic combinations.”
However, cows only pass one set of genetics to their calves, losing the exact combination of genes for the hybrid vigor effects.
Using a formula, however, heterosis can be accounted for.
“Literature suggests that as heterosis increases, longevity should increase by as much as 38 percent,” he explained.
On finding a handful of producers who kept records on crossbred cows, researchers used available data to determine that heterosis corresponded to an 11 percent increase in stay-ability at five years of age.
Comparing stay-ability between crossbred cattle and other breeds that do not have data also proved to be challenging, as well, as the data for crossbred cattle was expressed in terms of longevity, rather than stay-ability.
In a simulation, two herds were used, one with a cow retention rate adjusted for 50 percent stay-ability at five years of age.
“We readjusted the cow retention and age of the herd. The difference should have been an increase in longevity of the herd,” he explains. “We received an average of 0.77 years increase in stay-ability, compared to the 0.93 years suggested in the literature.”
“If we extrapolated that out to reach six years stay-ability, we saw a 12 percent increase due to heterosis,” Speidel said. “This is new research that will be coming out this fall.”