| | Ultrasound has been used in the beef industry for several decades as a non-invasive method to determine body composition. More recently, feedlots have used ultrasound on a large scale to sort cattle into management and optimal market end point groups during finishing. Scientific studies now show that real time ultrasound (RTU) measurements of fat thickness and ribeye area in pre-slaughter beef cattle result in correlations above 0.80 (1.0 means perfect correlation) with carcass data. In our research with cattle prior to slaughter, 70% of RTU ribeye area measurements were within 1 in. of the carcass measurements, while 80% of RTU fat measurements were within 0.05 in. of the carcass measurements. Researchers generally agree that ultrasound, since it is non-invasive and based on its relative accuracy, is the most promising technology to evaluate carcass merit in live beef cattle.
From a genetic perspective, we have been investigating the use of RTU in breeding animals to make selection decisions for improving carcass merit. Ideally, yearling RTU measurements on bulls and heifers could be used to estimate EPD for carcass traits, and therefore be used as tools to select replacements.
For three years, cattle at the Onefour research substation were used to develop carcass EPD based on RTU measurements. Yearling bulls and heifers had RTU ribeye area and fat thickness measurements taken. Steers that were siblings or progeny of these cattle had extensive carcass data collected after a standard finishing period. The genetic correlation between biologically equivalent traits should be one. Our results indicated that at the genetic level, the correlation between a yearling bull RTU ribeye area measurement and a steer carcass ribeye area measurement was approximately 0.70. Due to differences in age at measurement (i.e., yearling for the breeding animals versus about 15 months for the steers), differences in gender (i.e., intact breeding cattle versus steers) and differences in management, RTU and carcass measurements of similar traits may not be biologically equal. This means that it may be more appropriate to consider RTU and carcass measurements, even of similar traits such as live muscle area, as separate but correlated traits. In other words, RTU measurements on yearling breeding cattle are not simply a proxy measurement for steer carcass measurements.
The genetic correlation between steer carcass fat and yearling RTU fat in heifers was about 0.66, however, the same correlation with yearling RTU fat in bulls was only 0.23. These genetic correlations seem to indicate that fat deposition in breeding animals versus slaughter cattle is quite different. Also, it is apparent that steer carcass fat is more similar to heifer RTU fat than RTU fat in yearling bulls. The explanation of the lower genetic correlation among fat measures probably involves several gender and management effects. The implication for estimating fat EPD is similar to that for ribeye area, where fat could be considered separate but correlated traits according to whether measured on a yearling breeding animal or on a steer carcass.
Research will continue on the use of RTU in genetic improvement programs in several areas. In a collaborative project, we will investigate the relative value of RTU versus carcass measurements in genetic evaluation. This will lead to recommendations on appropriate testing programs to realize the most value from data collection, as well as answer questions about pre-selecting potential replacements on the basis of RTU data. Further, we will be looking at expected rates of genetic progress and increases in accuracy of genetic evaluation when selection is based on RTU versus carcass data, or a combination of both. Also, it is of interest to predict composite measures of carcass merit with RTU. Rather than evaluation of component traits alone such as ribeye area and fat, RTU may be effective in providing improvement tools for total yield as well as other economic traits.
Prepared By:
Dr. Denny Crews
Research Scientist, Beef Cattle Genetics
Agriculture and Agri-Food Canada, Lethbridge, AB
Southern Alberta Beef Review - April/May, 2001. Volume 3, Issue 2 |
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