Date of Award
Master of Science
William R. Backus
Charles S. Hobbs, James A. Corrick Jr
A study to determine the effects of initial subcutaneous fat thickness and grade of feeder heifers upon subsequent feedlot per-formance, carcass grade and yield, was conducted at the University of Tennessee's Blount Farm at Knoxville. The experiment involved 180 feeder heifers weighing from 420 to 615 pounds, purchased from graded feeder calf sales in the East Tennessee area. Grades represented were Choice, Good and Medium. The grades were based on Tennessee Department of Agriculture grading standards. Breeds represented were 141 Hereford, 29 Angus and 10 Hereford-Angus crosses. The average daily ration during the 140 day roughage phase was com silage, fed ad libitum, plus 6 pounds of concentrate. Heifers reaching 10 mm. or more of subcutaneous fat thickness as measured ultrasonically over the 1. dorsi between the twelfth and thirteenth rib, were slaughtered at the end of the 140 day roughage phase. Heifers not attaining 10 mm. of subcutaneous fat at the end of the 140 day roughage phase, were fed and 8:1 concentrate fullfeed ration until 10 mm. of subcutaneous fat was reached. It was found that initial feeder grade had a significant effect on average daily gain on roughage and average daily gain over the entire feeding period. Medium grade heifers gained significantly faster than Choice grade heifers. However, no significant differences were found in average daily gain between Medium and Good grades nor Good and Choice grades. Initial feeder grade did not significantly effect yield grade, carcass grade or percent retail yield. No significant differences were found for the effects of initial weight on average daily gain on roughage, average daily gain overall or carcass grade. However, initial weight did significantly affect yield grade and percent retail yield. Simple correlation coefficients of 0.002, 0.002, 0.06, 0.30, -.30 were found for initial weight on average daily gain on roughage, average daily gain overall, carcass grade, yield grade and percent retail yield, respectively. No significant differences were found for the effects of initial subcutaneous fat thickness on average daily gain on roughage, average daily gain overall or carcass grade. However, initial subcutaneous fat thickness did significantly affect yield grade and percent retail yield. These results indicated that each mm. increase in initial subcutaneous fat thickness resulted in a decrease of .16 of a percent in percent retail yield. Simple correlation coefficients of -.13, -.13, 0.13, 0.29, -.29 were found for initial subcutaneous fat thickness on average daily gain on roughage, average daily gain overall, carcass grade, yield grade and percent retail yield, respectively. The heifers were marketed when they reached 10 mm. of sub-cutaneous fat measured ultrasonically, at a point three-fourths the longitudinal distance of the 1. dorsi from the chine end, between the twelfth and thirteenth rib. Data collected from the 178 carcasses resulted in 67 percent grading Choice and 33 percent grading Good. Seventy-one percent of the Good carcasses graded high Good. In conclusion, this data indicated that initial feeder grade might possibly be used to predict feedlot performance. Initial subcutaneous fat thickness could possibly be used to predict carcass yield. Therefore, initial feeder grade and initial subcutaneous fat thickness might be useful to the feedlot operator to estimate feedlot performance and carcass yields.
Harrell, Irby Jackson, "The effects of initial subcutaneous fat thickness and grade of feeder heifers upon subsequent feedlot performance, carcass grade and yield. " Master's Thesis, University of Tennessee, 1971.