Document Type

Thesis - Open Access

Award Date


Degree Name

Master of Science (MS)

Department / School

Animal Science

First Advisor

Michael Gonda


beef, carcass merit, imaging laboratory, ultrasound


Ultrasound technology provides cattle breeders a relatively quick, non-invasive, and economical way to gather carcass data on live animals. Ultrasound provides the means to accurately predict body composition and develop estimated breeding values; however, national cattle genetic evaluations assume homogenous additive genetic and residual variances. These assumptions may be violated when estimating genetic merit for carcass traits by ultrasound because of differences in variance due to scanning technician and image interpretation laboratory. The objective of this study was to partition the phenotypic variance of measurements of carcass traits that were made using ultrasound into components attributable to additive genetic effects, scanning technician, contemporary group, and residual effects. Data for longissimus muscle area (LMA), percent intramuscular fat (IMF), and subcutaneous fat depth (SFD) were provided by the American Angus Association (AAA; N=65953), American Hereford Association (AHA; N=43180), and American Simmental Association (ASA; N=48298) representing a sample of animals scanned between 2015 to 2017. Data provided by each association included ultrasound carcass measurements, contemporary group, technician ID, imaging lab, and a three-generation pedigree for each animal. First, variance components for ultrasound carcass measurements were estimated with a univariate animal model for each breed and imaging laboratory separately by multiple trait derivative free restricted maximum likelihood. Genetic correlations between laboratories for longissimus muscle area, percent intramuscular fat, and subcutaneous fat were estimated with tri-variate animal models treating measurements from each image interpretation laboratory as a separate trait. Technician explained 12-27%, 5-23%, and 4-26% of variance for IMF, SFD and LMA respectively across all three breeds. Variance contributed by technician was often greater than variance contributed by additive genetics but almost always less than that explained by contemporary group. Genetic correlations between labs across breeds ranged from 0.79 to 0.95 for IMF, 0.26 to 0.94 for SFD and 0.78 to 0.98 for LMA. Most genetic correlations were relatively high (rg > 0.80). Overall, both technician and imaging laboratory contributed to phenotypic variation of ultrasound carcass measurements.

Library of Congress Subject Headings

Beef cattle -- Carcasses.
Beef cattle -- Composition.
Ultrasonic imaging.



Number of Pages



South Dakota State University

Included in

Beef Science Commons



Rights Statement

In Copyright