I suggested in my July column that carcass muscularity is becoming increasingly important in matching fed cattle to the requirements of the emerging era of grid pricing. My rationale was that muscle provides a way of enhancing both carcass dressout and retail product yield that is superior to the alternative method, the use of fat.

I had intended to devote this column to an economic analysis of the muscle vs. fat for dressout enhancement. But a curiosity got in my way-a curiosity about the relationships between differences in muscularity and fat to carcass quality, yield grade and dressing percentages.

In response to my curio-sity, I went to my computer file containing five years of data on the OK Feedout, an annual feeding trial for producers sponsored by the Oklahoma State University extension service. I broke out samples of high marbling (325 head) and low marbling (189 head) breeds. My findings were as follows:

Quality grade: As expected, the two groups differed widely on quality grade. The high-marbling group graded 72 percent Choice and the low-marbling group graded 30 percent Choice. On Prime and Select, the high-yield group graded 6 percent and 26 percent, respectively. None in the low-yield group graded prime and 70 percent graded Select.

I also looked at the distribution of quality grades according to ribeye sizes ranging from 10 square inches to 16 square inches, assuming that leanness would increase with ribeye size and quality grade would decline. With the exception of one ribeye size (15 square inches), the high-marbling group varied only 3 percentage points in their Choice grade distribution. The number of Choice grade steers in the low-marbling group tended to increase as ribeye size increased. But the reverse was true for those steers grading Select.

Yield grade: I analyzed the steers in terms of Yield Grade 1, Yield Grade 2 and Yield Grade 3. Again, as expected, there were wide differences in the profiles of two groups. The low-marbling group excelled in Yield Grade 1 and Yield Grade 3 with percentages of 44 percent and 4 percent, respectively; 51 percent were Yield Grade 2s.

Sixty one percent of the high-marbling steers were Yield Grade 2s and 30 percent were Yield Grade 3s; only 9 percent were Yield Grade 1s.

Dressing percentage: I examined both the high-marbling group and the low-marbling group in terms of the numbers falling into dressout percentage groups, as follows: 60-61, 62-63, 64-65, 66-67. The result showed the steers in each of the two groups splitting almost equally between those dressing out above and below 64 percent-51 percent and 49 percent for the high-marbling group and 49 percent and 51 percent for the low-marbling group.

Ribeye area: The ribeyes of the steers in this study ranged from 8.7 square inches to 19.6, but the two groups varied only about 1 square inch on the average. The low-marbling group had the highest average. But there is more to the ribeye factor than meets the eye. A large ribeye area on a large frame steer isn't always meaningful. The ratio of ribeye area to carcass hundredweight for the breeds in this study was nearly identical.

Discussion: Who among you hasn't heard the often-repeated advice to avoid single-trait selection in choosing and evaluating breeding animals? Perhaps the same perspective is implied by the data in this study. The bottom line in the emerging grid-pricing era isn't just quality or yield or dressing percentage or ribeye area; it is a combination of these factors. As seedstock and commercial breeders the reality is that generalities don't work in designing high dressing feeder cattle that work on the grid. Within any perspective, including this study, there are breed differences that defy averages.

I'll go back to the issue of using muscle and fat to enhance dressing percentage in next month's column by looking at the economic effects of each. There are sure to be some surprises!

To contact Fred Knop, write Drovers or send e-mail to fredlyn@aol.com