What’s Causing Carcass Composition.

continued from page 1

To make an “apples to apples” comparison, I went through our database and selected producers who have started shipping calf-feds in the last few months. I restricted my data sort to producers who also shipped the same kind of cattle during the same time a year ago, but did NOT feed Zilmax. I ended up with over 22,000 individual carcass data records to analyze. The bottom line is that these cattle are running about 0.60 square inches less REA in relation to carcass weight and are about .03 inches fatter than a year ago.

While that may not sound so different, the change in REA alone is increasing YG by about 0.2 and the fat is increasing it almost an additional 0.1. A total of 0.3 of a YG means that every carcass with a YG of 3.7 to 3.9 last year, is now a YG 4. Within our database, about eight percent of the total population has a YG of 3.7 to 3.9 during the last two years. Referring back to the table on page 1, that also just happens to be the amount of increase compared to a year ago. So small differences in fat and REA can make big differences in the YG 4 percentage.

The next question from producers seeing an increase in YG is “what would cause this?” Invariably, their first thought is genetics. My analysis was restricted to cattle with “the same genetics”, so I don’t think we can attribute any changes to genetics. Instead, phenotypic changes are often due to environment.

This past winter was unusually cold. Some feedlots have also told me that they really struggled with the variability from extreme cold to normal temperatures then back to extreme cold again.

Another factor could certainly be drought. Many of these calves were raised in areas that were at least moderately affected by drought over the last two to three years. This would include the time they were nursing and also when they were gestating in the cow. So, not only could forage quality and quantity be a factor while they were growing, but fetal programming could also have an impact as well.

Just to put things into perspective, heritability is a measurement of the percentage of variation of a trait, or phenotype, which can be attributed to genetics. While carcass traits are highly heritable, those heritability values are in the range of 0.30 to 0.35. That means only about a third of the variation is due to genetics and most of the remainder is attributed to environment.

The bottom line is that lately, carcasses have been a little fatter and significantly lighter muscled. Part of that is due to the absence of Zilmax, but there appears to be a distinct environmental component as well. Please call me at 866-877-2525 if you have questions about your grid performance.s

ribeye area to maintain the same YG. Insufficient REA in relation to HCW will increase the YG. That ratio is smaller this year, meaning the cattle are lighter muscled in relation to their carcass weight. In order to maintain the same REA:HCW ratio in this year’s cattle, the REA would need to be 0.42 square inches larger.

One reason why composition was different a year ago would be that the beta-agonist Zilmax® was still being used. The use of that product significantly increases HCW and REA while also decreasing fat thickness. During this time a year ago, slightly more than half of all USPB cattle were fed Zilmax.

However, in tracking those that were not fed Zilmax, a change in composition is still present. Not only are they slightly fatter, but they are also lighter muscled.

The chart below shows the relationship between REA and carcass weight for all USPB Kansas cattle. One way to evaluate this is to compare the actual REA to the required REA. Required REA is derived from a formula that is driven solely by HCW. It’s the REA that is required to have no impact on YG. It is what “average” should be for any given HCW. So when the actual is below the required (a negative value), then lack of muscling is increasing the YG.

The delivery year quarters in the chart that included Zilmax cattle are marked with an asterisk. The last data point on the chart for the third quarter of delivery year 2014 runs through May 10th which is about three weeks short of an entire quarter.

In the most recent two quarters, REA has decreased by about 0.60 square inches in relation to HCW. That’s enough to increase YG by 0.2 units. Obviously, part of the change is due to not feeding Zilmax. However, if you compare the most recent two quarters with the same period a year earlier for cattle NOT fed Zilmax, their REA has decreased 0.25 square inches. But, this is comparing all USPB cattle to a subset.

I’ve been getting a few calls lately from cattle feeders who are seeing some pretty large increases in YG 4’s on their home-raised calf-feds compared to a year ago. Some of those are seeing REA in relation to HCW that is up to two square inches smaller than a year ago.