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feed efficiency in beef cattle
By Jackie Atkins, Ph.D., director of science and education, American Simmental Association, Bozeman, Mont. There are stacks of scientific articles with evidence of improved growth and performance in crossbred cattle. Feed efficiency is a relatively new trait of study and more difficult to measure. Therefore, understanding the role of heterosis in feed efficiency traits is not as well understood. A recent article by California Polytechnic State University, San Luis Obispo professor and researcher Keela Retallick and colleagues published November 2013 by the Journal of Animal Science, Volume 91, pages 5161-5166) suggests improved efficiency in Simmental x Angus crossbred steers. This study compared feedlot performance and carcass traits in purebred Angus, purebred Simmental, Angus x Simmental, and Simmental x Angus over a two-year period (a total of 158 steers). The same sires (11 total) were used in the crossbred and purebred steers. The direct effects of breed, maternal breed, and heterosis were examined for the following feedlot performance traits: initial weight, final weight, gain, dry matter intake (DMI; how much food was consumed), gain to feed ratio (G:F; how much the steer gained compared to how much he ate), residual feed intake (RFI; difference between the actual feed intake and the expected intake based on energy requirements where more efficient animals have lower values), residual gain (RG; the rate of growth that is independent of feed intake; higher value is better), residual intake with body weight gain (RIG; combines RFI and RG to find efficient, fast growing animals independent of body weight). Similarly, effects of breed, breed of the dam, and heterosis were reported for hot carcass weight (HCW), longissimus dorsi muscle area (LM), back fat thickness, marbling score and yield grade. The authors reported several traits had direct breed effects which was in agreement with previous studies. Simmental steers had an advantage with larger initial and final weights but had reduced RG (less desirable) than Angus steers. The breed of the dam also influence initial and final weights again with larger steers from Simmental dams suggesting increased milking ability associated with increase growth of these offspring even after weaning. There was an increase in performance and efficiency in crossbred steers on the following traits: initial weight, G:F ratio, RG and RIG. In respect to the carcass traits, the authors report across breed differences in all traits that agree with previous reports. Simmental steers had an advantage in HCW, LM
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and yield grade while the Angus steers had increased back fat thickness and marbling scores. Calves from Simmental dams also had increased HCW. Marbling improved in the crossbred steers while all the other carcass traits were not affected by heterosis. There is currently a large feed efficiency trial going on with the collaboration of several research institutions, industry companies, and breed associations (www.beefefficiency.org). This feed efficiency study is collecting DNA, feed intake, growth and carcass data on 8,000 head of cattle from eight main beef breeds in the U.S. Approximately 2,400 cattle will be genotyped and used to develop molecular breeding values for feed efficiency, growth and carcass traits. As feed intake is such a difficult and expensive trait to measure, researchers will investigate DNA markers that may estimate efficiency more readily than measuring efficiency directly. Information gained on the genetic control of feed efficiency from such a large scale project could have a huge economic value to the U. S. beef industry. One of the researchers, Bob Weaber, Ph.D., of Kansas State University, estimated that a 2-pound improvement in RFI would save the U.S. beef industry nearly 1.2 billion dollars in one year. While the trial by Retallick and her colleagues has relatively few animal numbers, the findings support a role in improved feed efficiency in crossbred (SimAngusTM) beef cattle compared to the purebred steers. Hybrid vigor has long been known to boost performance in growth traits. It is interesting to discover that it may also increase feed efficiency in crossbred animals. In times of high feed costs and an increased need for sustainable agriculture, the importance of understanding the genetic control of feed efficiency can’t be overemphasized. The potential for selecting more efficient animals with the knowledge gained from the feed efficiency study could have large economic impact on the beef industry (a 1 percent increase in efficiency has the equivalent economic impact as a 3-pound increase in rate of gain). It will be interesting and important to follow future reports from these and other researchers digging into the genetic control of feed efficiency in beef cattle and the role heterosis plays in improving this economically important production trait.