Comparison of methods for estimating carcass fat content of young Charolais bulls in performance testing station

Abstract

With the purpose to integrate carcass composition in the selection criteria applied in performance testing stations, accuracy of four in vivo techniques for predicting carcass fatness was evaluated on a sample of young Charolais bulls ( n = 136) that were relatively homogeneous (standard deviation of carcass fat content: 2.2%) and representative of young bulls performance tested in France. Carcass composition was estimated from dissection of the 6th rib and the weight of internal fat. In vivo measurements were: (a) handling scores, (b) fat thickness measured on scans performed at the 10th and 13th thoracic and 3rd lumbar vertebrae, (c) speed of ultrasound through the back and the hind limb, (d) the diameter of subcutaneous adipose cells in a biopsy removed from the top of the thigh. Except for the latter technique, each value was the average of two measurements taken at proximate locations. The techniques were compared on their ability to explain variation in carcass fat in addition to that using live weight in a model with contemporary group effect fitted. Adipose cell diameter and the speed of ultrasound through the back ranked first and explained 42% of the variance in fat content. The speed of ultrasound through the hind limb explained slightly less: 31%, while handling scores and scanning explained only 12% to 17%. Taking into account these differences in accuracy and differences in repeatability and practicability of these four techniques, measurement of the speed of ultrasound through the back appears to be the method that is most potential for inclusion in performance tests in beef bulls.