Reporting from last week"s Beef Improvement Federation annual research meeting in Oklahoma City, Kansas State Graduate Research Assistant Kerri Bates detailed her two-year study trying to get a handle on whether selecting for calmer calves is having any effect on rates of Bovine Respiratory Disease once those animals reach confinement.
Anecdotally, Bates points out, there does seem to be a relationship between temperament and health, and producers believe calmer cattle tend to find their way into the hospital chute less often than the flighty ones. Other research over the past decade has theorized that since high-strung temperament leads to stress response, which in turn increases the body"s immune-system reaction to that chronic stress, temperament should be related to susceptibility to disease like BRD. And, in fact, cattle that indicate objective measures of high-strung temperament have been proven to be less productive and more likely to demonstrate lower immune-system competence.
If the seedstock industry could harness that knowledge and breed for better immune status through calmer temperament, Bates and others have suggested, it might help select for the genetics that could build calves better suited to resist feedlot BRD, which still costs the industry one out of every two calves that die on feed. Of course, such tools would have to start with identification of the phenotype resistant to BRD--no small task until we can find a way to challenge disease-resistant breed candidates without killing them. The two best proxy methods available to score temperament and thus conceivably the underlying physiological changes that contribute to reduced BRD resistance have been around for 50 years:
- Chute scores, which grade calves on a 6-point scale while they"re restrained, based on how much they struggle.
- Chute exit speed, which measures how fast calves bolt from the squeeze once released.
Using those scoring tools systemically, both of which have been shown to be moderately heritable, should help breeders begin to make selection decisions based on calmer temperament, and thus measurable and predictable resistance to BRD in the feedlot.
It all sounds perfectly logical. But is it true?
To find out, Bates" study, which you can read here, tracked nearly 2,900 crossbred steers across two seasons, shipped from a single Nebraska ranch source to a commercial Colorado feedlot. At feedlot placement and again when calves were run back through the chute for reimplantation, the research team measured each calf"s temperament via both chute score and chute exit speed. They also drew blood samples to check concentrations of two key bloodstream components that indicate immune function.
- The average chute score both at placement and at reimplantation was significantly associated with BRD incidence. Calves that were graded as more flighty or aggressive had more incidence of BRD. However, at the time they were run back through the chute for reimplantation, the calves that had been pulled and treated for BRD while at the feedlot showed a chute score that indicated they had become calmer. Whether that change was a true change in temperament based on the calves becoming accustomed to handling or some other factor (like the scorer"s subjectivity) is hard to say.
- None of the temperament measures reliably predicted the amount of pneumonia-related lung damage found in the calves after they were slaughtered.
- Exit speed out of the chute at first processing said nothing about whether the calf would need future BRD treatment. At the second processing, calves that were eventually pulled and treated for BRD left the chute more slowly than those that didn"t get pulled in the first year"s dataset; however, the result was flipped in the second year"s data. Therefore, the two years canceled each other; when the data were combined, no statistically significant difference was found in chute exit speed for cattle eventually treated for BRD vs. their non-treated peers. Bates suggests the unexpected effect could have been caused by poor handling at treatment that increased panic at second processing, confounding the results.
- At handling for reimplantation, calves bolting more quickly from the chute was predictive of need for BRD treatment: Every three and a third foot per second increase in the speed at which a calf left the chute increased the probability of BRD treatment by 17 percent.
- Although results seemed to contradict themselves, in that data suggested a higher chute score at reimplantation increased probability of BRD, while also suggesting calmer cattle were the ones that contracted BRD, when the data were reanalyzed Bates" results showed that it was the cattle on the extremes of the chute-score scale had a greater chance of experiencing BRD than their moderately temperamental peers.