95 Evaluation of variation attributable to lab and technician for measurements of beef carcass traits made using ultrasound

Abstract

Abstract Carcass data that is collected using ultrasound contributes to national genetic evaluation of beef cattle. Cattle are scanned by many technicians and the resulting images are processed by three laboratories providing data to breed associations. The Ultrasound Guidelines Council certifies technicians and laboratories as being proficient. However, there has been no comprehensive evaluation of non-genetic sources of variation that affect the data. The objective of this study was to partition the variance of ultrasound carcass measurements to animal genetic effects, ultrasound scanning technician and image interpretation laboratory. Ultrasound carcass data for longissimus muscle area, percent intramuscular fat, and subcutaneous fat depth were provided by the American Angus Association (n=65,971), American Hereford Association (n=43,380), and American Simmental Association (n=48,298). For each breed variance components were estimated for additive genetic effects of each animal, technician, contemporary group nested within technician and residual. Genetic correlations were estimated treating measurements from the different interpretation laboratories as separate traits. Across all three breeds, additive genetic effects explained between 15 and 30%, 11 and 25%, and 6 and 13% of the phenotypic variance for IMF, SQF, and LMA, respectively. Similarly, technician explained 12-27%, 4-28%, and 4-26% of the phenotypic variance; contemporary groups within technician accounted for 25-45%, 20-54%, and 43-73% of phenotypic variance. Among the image interpretation laboratories, the ratio of greatest to least residual variance was 3.96, 1.62, and 1.50 for IMF, SQF, and LMA, respectively. Genetic correlations between labs ranged from 0.79 to 0.95 for IMF, 0.64 to 0.94 for SQF and 0.78 to 0.98 for LMA. These results suggest the potential for the residual variances to be heterogeneous, particularly for IMF, depending on the image interpretation laboratory.