Beef Cattle Browsing
Editor: Dr. Stephen Hammack, Professor & Extension Beef Cattle Specialist Emeritus
June 2007
This newsletter is published by Texas AgriLife Extension – Animal Science. Media, feel free to use this information as needed and cite Texas A&M University Beef Cattle Browsing Newsletter, Dr. Steve Hammack.
EFFICIENCY vs. METHANE
Methane contributes to what is commonly called greenhouse gas omissions. Methane production by ruminant livestock is estimated to contribute 10 to 15 percent of emissions caused by human activity. Residual feed intake (RFI) is a measure of efficiency of conversion of feed to body weight gain. RFI measures the difference between actual feed intake and predicted intake required for body maintenance and gain. Therefore, more efficient animals have lower RFI values. Australian researchers in New South Wales used 76 Angus steers fed a barley-based ration for 70 days and measured relationships between RFI and methane production. The steers were from two closed genetic lines selected over 2.4 generations for either low or high RFI.
There was a significant relationship between RFI and daily methane production rate, with low RFI animals producing less methane. So, the more efficient animals produced less methane on less feed at comparable rates of gain. RFI explained only a small part of the total variation in methane production, but the authors concluded that selection for low RFI would “reduce methane emissions without comprising animal productivity”. (In fact, since RFI animals tend to be more efficient, the methane reduction might be viewed as a bonus.) Finally, in developing predictive equations, the authors suggested that the highest level of methane reduction would be found on low digestibility, high-roughage diets, which are the primary source of nutrition in beef cattle production. (J. Animal Sci. 85:1479)
BRAHMAN GROWTH & CARCASS GENETICS
Researchers at Texas A&M, Louisiana State University, University of Louisiana-Monroe, and Central Community College-Hastings, NB collaborated on a study of genetic parameters in 467 spring-born purebred Brahman steers (sired by 68 bulls) from 17 privately-owned Louisiana herds. At weaning, steers were commingled for grazing on ryegrass in Louisiana, shipped to South Texas to a commercial feedyard, and then processed in a nearby commercial facility.
Heritabilities were from 0.4 to 0.6 for slaughter weight, carcass weight, ribeye area, Yield Grade, Quality Grade, and calpastatin. Heritabilities were from 0.2 to 0.4 for hump height, marbling score, fat thickness, feedyard ADG, and shear force measured at both 7 and 14 days post-slaughter. Low (<0.2) heritability was estimated for skeletal maturity, lean maturity, and internal fat. Genetic correlations between traits were mostly from + 0.5 to – 0.5. However, correlation between calpastatin and 7-day shear force was 0.72, and between calpastatin and 14-day shear force was 0.74. The highest correlations were between fatness and tenderness; fatter cattle tended to be more tender, as correlation between fat thickness and 7-day shear force was -0.82 and between 7-day shear force and Yield Grade was -0.90. The authors concluded that genetic improvement can be made for carcass and palatability traits in Brahman cattle. (J. Animal Sci. 85:1377)
ADAPTABILITY – WHAT IS IT?
Recently, I attended a conference made up mostly of animal breeders, i.e, researchers who study beef cattle population genetics. It was mentioned that the term “adaptability” can mean different things to different people. In population genetics, adaptability refers to how well suited is a biological type to a particular set of environmental conditions, also sometimes called “fitness”. This is often defined as being able to survive and reproduce. From a practical standpoint, this should probably be extended to not only survival and reproduction but also to include production, product, and economics. Such adaptability typically occurs over long periods of time in a population maintained in the same environment.
But to many, adaptability means how quickly and successfully an animal adjusts when moved from one environment to another. To avoid confusion, this might be better thought of as becoming acclimated, rather than adapted.
Maybe we should not use adaptability but think of suitability or fitness and acclimatibility or adjustability. Regardless, both characteristics can be important. We should strive to identify and produce types of cattle that are well suited to their primary environment, but also are able to adjust reasonably well to different conditions.
EFFECT OF FEEDING FATS ON MEAT COMPOSITION AND QAULITY
Edible beef products generally have relatively high levels of saturated fatty acids and trans fat (“bad”) and low levels of polyunsaturated fatty acids (“good”). Cattle convert unsaturated fats in the rumen to intermediate and saturated forms, and the level of each can vary. This ultimately leads to differences in fatty acid composition of body fats, which can affect meat quality. Among other effects, more unsaturated fat can be associated with higher oxidation and more off flavor and odor. University of Georgia and Clemson University researchers wanted to know how feeding some fats might be involved in this process. They divided 36 Angus X Hereford heifers fed high-concentrate rations into groups of control (CON), 4% corn oil supplement (OIL), and 2% partially rumen-protected conjugated linoleic acid supplement (CLA).
At a statistical significance level of P<.05 for all of the following fat and taste-panel results, there was no difference among the three groups, in either ground beef or ribeye steaks, in fat oxidation, saturated fat levels, or unsaturated fat levels. There were some differences in levels of trans fat, with CON tending to be lower and CLA higher.
In ground beef, CLA had lower taste-panel juiciness ratings, CON was more tender than CLA (with OIL intermediate), CON was higher in off flavor, and there were no differences in beef flavor. In steaks, CON was juicier than OIL (with CLA intermediate) and there were no differences in off flavor.
Though several statistically significant differences were found, mostly in favor of CON, the differences were relatively small and the authors concluded that dietary fat supplementation resulted in small changes in shelf life and taste-panel factors. (J. Animal Sci. 85:1504)
IS SIZE STILL INCREASING IN ALL BREEDS?
First, what is “size”? The best measure of size or body mass is weight, not height or some other dimension. Weight is what is involved in nutritional requirements, and also what is sold. So, it’s how big, not how tall. Somewhere in the 1960s, our established breeds started selecting for bigger cattle. Most of the Continental European breeds imported starting in the late 60s were bigger than established breeds. And selection for increased size has generally continued, in varying degrees. Let’s look at what has happened in two of our most numerous breeds, a British and a Continental.
Since 1980, genetic trend in Angus has increased 38 lb for Weaning EPD and 71 lb for Yearling EPD, with a steady increase for both. (Over the same period, averaged for bulls and heifers, actual reported weaning weight has gone up over 125 lb and yearling weight almost 200 lb.) Change has been slower in most Continentals but, since 1980, Simmental EPD has increased 11 lb for weaning, essentially stabilizing since about 1990, and 24 lb for yearling. (The U. S. Meat Animal Research Center says most of our most numerous breeds currently weigh about the same.) Similar trends can be seen in all of the more numerous breeds.
However, I recently ran across data for a less numerous breed, Red Poll. Since 1980, EPD for weaning has increased only 4 lb and yearling only 5 lb, and cattle of this breed were relatively small to begin with. There are probably some other lesser know breeds with similar trends. Is this good or bad? It depends, on what sort of genetics you want. But it does seem there is still plenty of genetic variation to choose from among breeds, as well as within breeds, so you should be able to find whatever is needed or wanted. (Genetic evaluation data from American Angus Association, American Simmental Association, and American Red Poll Association.)