Factors Influencing Ultrasound Estimates of Carcass Traits and their Relationships with Body Weight, Gain, Scrotal Circumference and Hip height in Feedlot Bulls

Abstract

Morsy, N.H.A., Makrechian, M., El-Feel, F.M.R. and Hassan, H.A. 1998. Factors influencing ultrasound estimates of carcass traits and their relationships with body weight, gain, scrotal circumference and hip height in feedlot bulls. J. Appl. Anim. Res., 14: 159–170. Body weight (WT), scrotal circumference (SC), hip height (HHT) and ultrasound estimates of backfat thickness (BF), lean meat yield (LMY) and rib eye area (REA) were recorded in 64 bulls from two synthetic breed groups. The bulls were fed either a high concentrate (85% grain) or low concentrate (55% grain) diet. WT, SC, HHT, BF, LMY and REA were recorded on days 100, 128 and 156 of feedlot test. The data were analyzed by general linear model analysis of variance to study the effects of energy level, breed group and their interaction on ultrasound estimates of BF, REA and LMY and their changes in feedlot test. Stepwise regression analysis considering the separate effects of each diet and breed group was applied to study the relative influences of final WT, SC and HHT on variation in the ultrasound estimates. The results indicated that HHT did not have any significant association with the carcass traits. Breed group and level of energy did not have significant effects on the relationships between WT and SC with BF which were significant and positive. The regression coefficient of BF on average daily gain (ADG) was significant only on high concentrate diet. There was significant difference in the regression coefficient of REA on WT between the two breed groups. The regression of REA on BW was greater in DSX breed. The regression coefficients of LMY on WT and SC were negative and significant. The regression of LMY on ADG was significant only at high level of concentrate in the diet. The level of energy in feedlot diet was a significant (P<0.01) source of variation for all the ultrasound carcass estimates. The bulls on high energy diet were significantly fatter (8.1 vs 4.9 mm BF) and had larger rib eye area (79.4 vs 64.3 cm2) compared to those on low energy diet. Breed group did not have any significant effects on the ultrasound carcass measurements. The results indicated that in general WT, SC and ADG had strong influences on the carcass traits and therefore, these measurements could be used to improve the prediction of carcass composition. However, these relationships could be influenced by the genotype of animals and the level of energy in the feedlot diet in young beef bulls.