Live Animal, Carcass and End Point
Real-Time Ultrasound: What Does Image Quality Mean to Genetic Evaluation?
Abstract:
Ultrasonic measurements for the traits of ribeye area (UREA), percentage intramuscular fat (UPFAT) and 12th-rib fat (UFAT) and their associated image quality scores (IQ) obtained from Ultrasound Guidelines Council (UGC) certifications in Ames, Iowa, from 2002-2006 were utilized to quantify the relationship between IQ and the absolute value of prediction bias (ABS). More than 5,000 records were used for each trait.
Currently, IQ are utilized as a subjective criterion to partially determine the proficiency of an ultrasound technician. IQ represents a 1-7 scale where those images classified as a 1 or 2 are acceptable, 3-5 are marginal, and images scored as a 6 or 7 are rejected and not interpreted in practice. Only IQ scores of 1-5 were used in the current study. The GLM procedure of SAS was used to predict ABS with potential explanatory variables of interpreting technician, IQ, machine, animal and year. For UPFAT an additional explanatory variable of categorical nature was added (CAT). CAT was a subjectively defined categorical variable used to account for any potential differences in predictive ability by animals that had different levels of ether extract values that are used as the carcass reference for UPFAT.
IQ was not statistically significant in the prediction of ABS for the traits of UREA and UPFAT. Although IQ was significant (P=0.0018) for the prediction of ABS for UFAT, IQ did not numerically contribute to the predictive ability of the model.
The results from the current investigation suggest that the subjective measure of IQ is not strongly related to ABS and, as a consequence, bias should not be introduced into genetic evaluations by including multiple IQ scores in a contemporary group for any of the three traits considered here. As a caveat to the objectives of the current study, the effects of machine and CAT, as well as their interaction, were significant in the prediction of ABS for UPFAT. Further investigation is warranted to determine if differences between interpreting software exist with particular regards to the reduction of variation for the trait of UPFAT.
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