|Rouquette, Jr, F - TEXAS A&M|
|Brown, Jr, A - UNIV OF ARKANSAS|
Submitted to: Grassland International Congress
Publication Type: Proceedings
Publication Acceptance Date: September 25, 2000
Publication Date: N/A
Interpretive Summary: Real-time ultrasound also has potential for measuring compositional traits in grazing experiments. Many cattle producers are vertically integrating their operations (i.e., retaining ownership of feeder calves in the feedlot) and cattle marketing is becoming more value-based. Small and large farmers will need awareness of body condition and composition generated with their forages and management systems. A study was conducted with steers grazing rye-ryegrass pastures to evaluate breed type, initial body weight, and initial ultrasonic measures as sources of error in measuring compositional traits with ultrasound technology in grazing studies. The study was conducted with steers that had Angus x Brahman, Simmental x Brahman x Angus, and Simmental x Brahman x Hereford breeding. Ultrasonic scans were taken over the ribeye between the 12th and 13th ribs at the start and conclusion of grazing. Breed type did not affect external fat measurements, but did affect ribeye area. Final measurements of both compositional traits further showed to depend on initial body weights of the steers. Results of the study showed researchers should account for breed type and initial body weight differences when designing grazing experiments for measuring compositional traits with ultrasound technology. This research provided recommendations for improving the precision of using real-time ultrasound in grazing experiments. These experiments will provide technology to small farmers that want to be aware of how pasture management affects body condition and composition, and subsequent feedlot performance and efficiency.
Technical Abstract: Real-time ultrasound has potential use for measuring compositional traits in grazing studies. Sources of error with this application must be identified for designing experiments with adequate precision for determining treatment effects. A study was conducted to evaluate breed type (Angus x Brahman,AB; Simmental x Angus x Brahman, SBA; Simmental x Brahman x Hereford, SBH), initial body weight, and initial ultrasounic measures as sources of experimental error in the analyses of external fat (EF) depths and longissimus dorsi areas (LDA). Steers were scanned with an ultrasound at the start and conclusion of a grazing study with ryegrass (Lolium multiflorum L.) that was designed to examine stocking rate and grazing method effects on steer performance. Breed type did not affect (P > 0.10) final or increases in EF, and curvilinear trends were similar (P > 0.10) among the breed types over the range of average daily gains (ADG; range = 0.03 kg d-1 to 1.62 kg d-1). The three breed types showed curvilinear increases in LDA as ADG increased, but the trends were different (P < 0.05) between SBH and the other two types. Final and increases over the experimental period showed correlations (P < 0.05) with initial body weight and ultrasonic measures. Results of the study indicate that allotting cattle to pastures based on a combination of breed type and body weight should improve precision in detecting treatment effects.