Date of Award
Master of Science
William R. Backus
J.B. McLaren, J.A. Corrick, Jr.
One hundred-eighty feeder heifers (150 Hereford, 29 Angus and one crossbred) of Choice, Good and Medium feeder grades were fed to determine the effects of initial subcutaneous fat thickness, feeder grade and initial weight on their feedlot performances and carcass quality and cutability. Heifers were purchased at graded feeder calf sales in East Tennessee.
After an adjustment period of three weeks, the heifers were fed corn silage ad libitum, treated at the time of ensiling with 10 pounds each of urea and ground limestone plus six pounds of concentrate per head per day, for 110 days, and then full-fed a concentrate ration of eight parts ground shelled corn to one part 41 percent cottonseed meal, to finish the heifers at an ultrasonically estimated fat thickness of 10 mm. or 8 mm.
Initial weight was found to have a small, but significant (P < .001) effect on final weight, carcass weight, yield grade and estimated percent retail yield.
Feeder grade had a highly significant (P < .01) effect on dressing percent, and a very highly significant (P < .001) effect on carcass conformation grade. Variation in feeder grade did not significantly influence the other measures of performance or carcass characteristics. Simple correlations of feeder grade with roughage phase average daily gain, overall average daily gain, yield grade and percent retail yield were -0.06, -0.04, 0.14 and -0.17, respectively.
An additional 4.41 percent of the variation in overall average daily gain was explained by variation in initial subcutaneous fat when initial weight and grade were held constant. Initial fat also accounted for an additional 5.29 percent of the variation in carcass fat, 2.35 percent of the variation in yield grade, and 1.74 percent of the variation in retail yield. These percentages were small and non-significant (P > ,05) in all cases. In comparison, fitting initial condition grade to the original model accounted for an additional 11.97 percent of the variation in overall average daily gain, 10.36 percent of the variation in carcass fat, 4.70 percent of the variation in yield grade, and 3.85 percent of the variation in estimated retail yield. The gross simple correlation between initial fat and initial condition grade was 0.57. The correlation between feeder grade and type grade was 0.88. Correlations were obtained for feeder grade with initial fat and initial condition grade of 0.41 and 0.76, respectively, and for type grade with initial fat and initial condition were 0.09 and 0.14, respectively, indicating initial fat and initial condition are inseparable parts of feeder grade.
Heifers that were slaughtered when the ultrasonically estimated fat thickness reached 8 mm. produced carcasses comparable to those of heifers slaughtered at 10 mm. fat thickness. There were no significant (P > .05) differences between the two fat levels in carcass grade, yield grade and percent retail yield. The heifers fed to 8 mm. subcutaneous fat finished 10 days earlier than the 10 mm. level heifers, and cost per hundredweight gain overall was in favor of the 8 mm. level heifers by $0,85.
Results of this experiment indicate that either of the three grades may be fed with equal success, and that price spreads between feeder grades of equal weight may be the most important consideration in purchasing feeder heifers.
Rowland, David M., "Effects of Initial Subcutaneous Fat, Grade, and Weight of Feeder Heifers on Their Subsequent Feedlot Performance and Carcass Characteristics. " Master's Thesis, University of Tennessee, 1972.