16 August 2014

6 minute read

Cattle producers of all types—from the cow-calf, stocker and feedlot sectors—historically have selected for and preferred to manage calmer animals not only because they are safer for handlers to be around, but they also seem to gain weight faster and have fewer health issues.

Recent research involving many universities, including Kansas State, examined the genetics of bovine temperament and how it relates to two important aspects of production: immune function, specifically animals’ susceptibility to bovine respiratory disease (BRD), and carcass merit. It found, as previous research has also indicated, that temperament is a moderately heritable trait producers can select for in their herds.

Bob Weaber, beef breeding and genetics specialist for K-State Research and Extension and one of the researchers on the project, said this study showed that animals with a more favorable temperament gained better on feed compared to more excitable animals. Because of this, they were overall more mature at harvest and seemed to have carcass fat, which is desirable to an extent for better quality grades. But, at extreme levels, the extra fat is undesirable for both quality and yield grades.

Temperament and its relation to the disease component of the study was a little harder for the researchers to separate, he said, and yielded some somewhat surprising findings.

About the study

Weaber worked with many other researchers on the project that was led by Mark Enns, professor of animal sciences at Colorado State University. They collected data in 2007 and 2008 as part of a large study to look at the genetics of feedlot cattle health.

“It was an involved project in that it took a lot of human hands to pull off,” Weaber said. “We processed data on more than 2,500 head of steers fed in southeast Colorado during those two years.”

It took the researchers about five days to process the cattle upon arrival at the feedlot, he said. Ultrasound information helped the researchers determine the animals’ body composition, both when they were placed on feed and at subsequent processing about 80 days into the feeding period. The researchers also collected temperament data at these times and monitored the animals closely for disease, specifically BRD, at all times.

The researchers measured temperament in two ways: chute score and exit velocity. The chute score scale defined by the Beef Improvement Federation (http://www.bifconference.com/bif2012/proceedings-pdf/05randel.pdf) ranges from 1 to 6, where calmer animals are at the lower end and most aggravated cattle, the ones Weaber said “test every weld on the squeeze chute,” are at the higher end.

“In this case, most of the animals scored 2, 3 and 4, which is typical of beef cattle categorization in the United States,” he said.

Exit velocity was calculated based on the time it took an animal to cover a defined distance of 6 feet, after it was released from the chute.

Additionally, a blood sample from each animal was taken during processing to examine concentrations of cortisol and interleukin-8 (IL-8). High levels of cortisol indicate stress in cattle, while high levels of IL-8 show a more active or functional immune system, Weaber said.

Health component’s surprising results

At first thought, producers might desire low levels of cortisol and high levels of IL-8 in their cattle, Weaber said, as these cattle would likely be calmer and have stronger immune responses. However, this study found that concentrations of IL-8 had a positive relationship with animals classified with BRD, while concentrations of cortisol had a strong negative genetic relationship with BRD—an interesting and unexpected finding of this study.

Weaber said he understands this finding to mean that a strong immune response could cost an animal a lot of energy. Animals with strong immune responses, and higher levels of IL-8, might generate fevers and have other negative responses that could affect performance.

“Animals that get sick, manage the disease in a more moderate way and tolerate the infection, versus have a large immune response, actually perform better,” Weaber said. “These animals don’t spend as much energy fighting the disease. They do it sufficiently, obviously, and survive the incidence of BRD.”

The results of this particular project helped stem a larger U.S. Department of Agriculture project examining the genetics and genomics associated with BRD, he said. In this study (http://www.brdcomplex.org/Index.html), researchers are doing a series of inoculations on animals to make sure each one is exposed to BRD disease pathogens and then monitoring how they respond to it.

Another surprising finding of the research that challenged interpretation, Weaber said, was the second chute score observation on the animals that occurred 80 days into the feeding period, as it related to BRD incidence. The researchers found that animals of higher chute score, the ones with less desirable temperament, had a substantially lower incidence of BRD.

Observational data from past studies, he said, has shown that animals respond differently to handling over time. Some animals acclimate to human handling when they have positive experiences and become easier to handle.

“I wonder if the animals that had BRD early in the feeding period, which is when most of them did, were handled more and had lower chute scores the second time around,” he said. “That might create that inverse relationship we observed in the data.”

Carcass merit somewhat expected

The researchers found that animals with genetics to be more temperamental, based on chute scores, typically had genetic merit for slightly heavier carcass weights, slightly larger ribeye areas, numerically lower, more favorable yield grades, but slightly worse marbling scores compared to calmer cattle. Those were all relatively weak relationships though, Weaber said.

Stronger relationships, he said, existed between carcass merit and concentrations of cortisol and IL-8 in the blood. These results were somewhat different than the relationships observed between carcass merit and temperament scores.

“We found animals that had genetic merit for elevated cortisol upon arrival at the feedyard were associated with genetic merit for lighter carcass weights at the end of the feeding period—an indicator they weren’t expected to perform quite as well,” Weaber said. “They also were genetically associated with slightly lower marbling scores and smaller ribeye areas.”

IL-8 concentration from a genetics standpoint, he said, was positively associated with hot carcass weight and marbling score, meaning those cattle with higher immune response had the genetic potential to be heavier and fatter. IL-8 concentration did not have a relationship with ribeye area and had a slight positive genetic association with yield grade, meaning it related to less desirable, higher yield grades.

“All of this suggests that more excitable cattle will weigh and gain less throughout the finishing phase than their calmer peers,” Weaber said.

Weaber recommends that cattle producers practice low-stress animal handling through Beef Quality Assurance (BQA) training. Being gentle and moving animals slowly pays dividends both in the learned behavior of the animals and the subsequent elevation levels of cortisol and stressors that impact an animal’s immune function.

“The more things we can do right in handling of cattle above and beyond what their genetic predisposition may be certainly helps,” he said.

August 2014