Feedlot performance and carcass traits of feeder cattle sorted by hip height and ultrasound determined backfat

Call number: LD2668 .T4 ASI 1989 H46Master of ScienceAnimal Sciences and Industr

Partitioning Variation in Measurements of Beef Carcass Traits Made Using 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 \u3e 0.80). Overall, both technician and imaging laboratory contributed to phenotypic variation of ultrasound carcass measurements

The relationship between ultrasound measurements and carcass fat thickness and longissimus muscle area in beef cattle

Five hundred thirty-four steers were evaluated over a 2-yr period to determine the accuracy of ultrasonic estimates of carcass 12th-rib fat thickness (CFAT) and longissimus muscle area (CLMA). Within 5 d before slaughter, steers were ultrasonically measured for 12th-rib fat thickness (UFAT) and longissimus muscle area (ULMA) using an Aloka 500V real-time ultrasound machine equipped with a 17.2-cm, 3.5-MHz linear transducer. Overall, correlation coefficients between ultrasound and carcass fat and longissimus muscle area were 0.89 and 0.86, respectively. Correlations for UFAT with CFAT were similar between years (0.86 and 0.90), whereas the relationship between ULMA and CLMA was stronger in yr 1 (r = 0.91; n = 282) than in yr 2 (r = 0.79; n = 252). Differences between ultrasonic and carcass measurements were expressed on both an actual (FDIFF and RDIFF) and absolute (FDEV and RDEV) basis. Mean FDIFF and RDIFF indicated that ultrasound underestimated CFAT by 0.06 cm and overestimated CLMA by 0.71 cm2 across both years. Overall mean FDEV and RDEV, which are indications of the average error rate, were 0.16 cm and 3.39 cm2, respectively. Analysis of year effects revealed that FDIFF, FDEV, and RDEV were greater (P \u3c 0.01) in magnitude in yr 1. Further analysis of FDEV indicated that leaner (CFAT \u3c 0.51 cm) cattle were overestimated and that fatter (CFAT \u3e 1.02 cm) cattle were underestimated with ultrasound. Similarly, steers with small CLMA (\u3c71.0 cm2) were overestimated, and steers with large CLMA (\u3e90.3 cm2) were underestimated. The thickness of CFAT had an effect (P \u3c 0.05) on the error of UFAT and ULMA measurements, with leaner animals being more accurately evaluated for both traits. Standard errors of prediction (SEP) adjusted for bias of ultrasound measurements were 0.20 cm and 4.49 cm2 for UFAT and ULMA, respectively. Differences in SEP were observed for ULMA, but not UFAT, by year. These results indicate that ultrasound can be an accurate estimator of carcass traits in live cattle when measurements are taken by an experienced, well-trained technician, with only small differences in accuracy between years