Date of Award
Master of Science
Food Science and Technology
H. Dwight Loveday
Jim Riemann, Frank Masincupp, E.R. Livdall
The purpose of this study was to determine the potential of various subjective and objective evaluations of feeder pigs predicting USDA pork carcass grades. Feeder pigs (N=220) representing U.S. No. 1-3 feeder grades purchased from a Tennessee feeder pig sale were weighed, measured, subjectively evaluated and photographed from which several linear measurements were taken. Subjective evaluations included frame height, frame length, overall frame, muscle score, body width, estimated fatness, and substance of bone. Objective measurements obtained were body depth, hock length, height from belly to floor, poll to tail length, shoulder to tail length, height of midpoint between shoulder and tail and ultrasonic fat measures at the last lumbar, last and first rib regions. A scatter plot diagram of weight versus poll to tail length was developed to allot feeder pigs to slaughter weights of 91, 104 and 118 kg (SWI, SWII, and SWIII, respectively). Animals were slaughtered as they reached the assigned endpoint weight (± kg), standard carcass measurements were taken and one side was standardized (Grisdale et al., 1984) and fabricated into four lean cuts (Cole, 1951). Prediction equations were developed by stepwise regression for USDA pork carcass grades (1984) utilizing feeder pig subjective and objective traits with R2 values ranging from .20 to .66. Equations derived from objective measurements and from SWI, II and pooled slaughter weights tended to have lower R2 values than equations using subjective evaluations and SWIII. The best model was developed from SWIII pigs, carcass grade = 5.88 - .44 (frame length) + .26 (frame height) - .21 (muscle score) - .64 (sex), R2 = .66. These data suggest that characterization of feeder pigs may be useful in predicting slaughter potential.
Furthermore, gilts had superior carcass grades as compared to barrows, especially at the heavier slaughter weights with the average carcass grade for barrows and gilts, 3.30 and 1.92, respectively. Subjective evaluations of feeder pigs for frame length and muscle score were found to be as effective as feeder pig grade in predicting slaughter potential with 63% of pigs with the largest muscle score yielding a U.S. No. 1 carcass. Gilts were found to be leaner as compared to barrows at all fat measurements with larger loineye areas and longer carcasses. The greatest differences were found at SWIII with average backfat for barrows and gilts, 42.21 and 36.75 mm., respectively. The carcasses were deboned and chemical analysis performed on each primal cut and the percent carcass fat was calculated. Gilts were significantly leaner at all slaughter weights with percent fat at SWIII for barrows and gilts 39.58 and 31.14 per cent, respectively.
Pace, Robert D., "Effect of subjective and objective evaluations in determining carcass composition of feeder pigs fed to 91, 104, and 118 Kilograms. " Master's Thesis, University of Tennessee, 1986.