By Lance Bauer, Director of Breed Improvement & Western Field Representative
The end goal of the cattle industry is to produce beef to feed a growing population. At harvest there are many measurements that are taken to determine the value of a carcass. Some of these traits are; rib eye area, marbling and fat thickness. These traits are all higher in their heritability (0.4-0.6) than many of the other weight and production traits that are measured (0.1-0.4). This means that you can make fairly rapid genetic progress for carcass traits. However, it is hard to measure carcass traits without harvesting an animal, so we use ultrasound to estimate REA, intramuscular fat (IMF), as well as rib and rump fat. The ultrasound will have to be done by a certified ultrasound technician and should be done between 320 and 550 days of age for the data to be included in the genetic evaluation.
Rib eye area is a measurement of the longissimus muscle and is taken between the 12th and 13th rib. REA is an indicator of overall muscling in an animal and is used in the calculation of yield grade. Animals that have a larger REA will adjust the yield grade of a carcass down, which is good because yield grade 4 and 5 animals receive a discount. When an animal is harvested a good way to receive a small premium is to have animals that are yield grade 1 and 2. Rib eye areas have been averaging around 13 square inches over the last few years and this is a very acceptable size for REA. Using ultrasound to measure REA is a good selection tool and the data reported back to the association is important in the calculation of the REA EPD.
Another trait that relates to yield grade is the animal’s fat cover. When using ultrasound two different measurements of fat cover are taken, one is over the ribs and the other is on the rump. When an animal is harvested the fat over the ribs is used to determine the base yield grade. An animal with between .4 and .6 inches of fat cover will start off as a base yield grade 3. Thinner animals will have lower numerical yield grades than fatter animals. Again, this is data that is important to gather and turn in, in order to calculate the Fat EPD.
The final trait that can be measured using ultrasound for carcass is the intramuscular fat or IMF. IMF is directly related to marbling, and marbling along with the age of an animal are used to calculate a quality grade. In the U.S. quality grade system, Prime is the highest quality, followed by Choice, then Select and finally Standard. The higher the percent IMF the higher the quality grade is expected to be. Quality grade dictates the price of the final product and many times is evaluated by looking at the Choice-Select Spread. IMF is another great selection tool and should be measured in order to help make mating decisions and to calculate the IMF EPD.
All of these carcass traits are important to measure using ultrasound, to help the producer make better mating decisions. While the Beefmaster is a maternal breed it is important to keep acceptable carcass values for the commercial producer using our bulls. Recording all of these measurements also helps in the calculations for carcass EPDs and all of the carcass traits are weighted into the $T index. The $T index was developed looking at weight as well as quality and yield grades. This series will continue with an explanation of contemporary groups and how they are used.