|Greiner, Scott - VIRGINIA TECH UNIV|
|Rouse, Gerald - IOWA STATE UNIV.|
|Wilson, Darrell - IOWA STATE UNIV.|
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 22, 2002
Publication Date: March 1, 2003
Citation: Greiner, S.P., Rouse, G.H., Wilson, D.E., Cundiff, L.V., Wheeler, T.L. 2003. The relationship between ultrasound measurements and carcass fat thickness and longissimus muscle area in beef cattle. Journal of Animal Science. 81:676-682. Interpretive Summary: Results from this study indicate that ultrasound technology has the potential to determine fat thickness and longissimus muscle area with a high degree of accuracy when done by an experienced, well trained technician. Therefore, ultrasound can be used to describe carcass traits in live cattle and allow for selection and management decisions to be made. Differences in accuracy for ultrasonic measurements across years emphasize the importance of proper maintenance of technique by technicians, and the need for periodic proficiency testing. The strong relationship between ultrasonic measurements of rump fat and body wall thickness with carcass 12th-rib fat thickness suggests the need for further investigation of these variables as additional indicators of composition.
Technical Abstract: Five hundred thirty four steers were evaluated over a two year period to determine the accuracy of ultrasonic estimates of carcass 12th-rib fat thickness (CFAT) and longissimus area (CREA). Within 5 d prior to slaughter, steers were ultrasonically measured for 12th-rib fat (UFAT) and longissimus area (UREA) using an Aloka 500V real-time ultrasound machine equipped with a 17.2 cm, 3.5 MHz linear transducer. Overall, correlation coefficients between UFAT and UREA with CFAT and CREA were 0.89 and 0.86, respectively. Correlations for UFAT with CFAT were similar between years (0.86 and 0.90), while the relationship between UREA and CREA was stronger in year 1 (r = 0.91, n = 282) than in year 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 0.06 cm and overestimated CREA 0.71 cm**2 across both years. Overall mean FDEV and RDEV, which are an indication of the average error rate, were 0.16 cm and 3.39 cm**2, respectively. Analysis of year effects revealed FDIFF, FDEV, and RDEV were larger (P < 0.01) in magnitude in year 1. Further analysis of FDEV indicated that leaner (CFAT < 0.51 cm) cattle were overestimated and fatter (CFAT > 1.02 cm) cattle were underestimated with ultrasound. Similarly, steers with small CREA (< 71.0 cm**2) were overestimated and steers with large CREA (> 90.3 cm**2) were underestimated. The thickness of CFAT had a significant (P < 0.05) effect on the error of UFAT and UREA 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 cm**2 for UFAT and URERA, respectively. Differences in SEP were observed for UREA, 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. Although significant (P < 0.01) differences were noted for accuracy variables between years, these differences were small in magnitude.