|Rouquette, Jr, F - TEXAS A&M UNIV|
|Miller, R - TEXAS A&M UNIV|
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 8, 2000
Publication Date: N/A
Interpretive Summary: Beef cattle production and marketing in the U.S. is presently changing to enhance product quality. Many cattle producers have vertically integrated their operations from cow-calf to stocker and/or to feeder. New approaches to grazing research will be needed to develop technologies for these producers. Two grazing experiments evaluated the use of real-time ultrasound for determining treatment effects on carcass-related traits for stocker steers. One experiment measured changes in backfat and ribeye area with increased levels of daily fed ground corn for steers grazing bermudagrass, and the other determined stocking rate effects on backfat thickness and ribeye area for steers grazing a mixture of 'Maton' rye and 'TAM90' ryegrass. Backfat thickness and ribeye area for steers on bermudagrass increased with increases in levels of daily consumed corn, and both of the measures for steers on the rye-ryegrass mixture decreased with increases in stocking rate. Real-time ultrasound was therefore shown to b effective in determining treatment effects on carcass-related traits. This technology can be used as a research tool in developing management systems for improving the profit potential of cattle production when ownership is retained from stocker to feedlot.
Technical Abstract: Real-time ultrasound technology has potential as a method for measuring changes in body condition and carcass-related traits of cattle in grazing trials. Ultrasound scans were collected for yearling steers at the start and finish of two separate grazing experiments to determine if measures of fat thickness (FT) over the 12th - 13th ribs and longissimus dorsi (LD) area can be taken with adequate precision to detect treatment effects on these traits. One grazing trial was conducted with common, and mixtures of common with'Tifton-44', and 'Midland' bermudagrasses [Cynodon dactylon (L.) Pers.] using commercial steers to evaluate the effects of corn supplementation (CS) on steer performance, and the other trial was conducted with a 'Maton' rye (Secale Cereale L.)- 'TAM90' ryegrass (Lolium multiflorum L.) mixture using three cattle breed types to determine stocking rate (SR) effects on steer performance. For the supplementation study, accretion in FT between the 12th and 13th ribs increased nonlinearly (P<0.10) and LD area accretion increased linearly (P<0.05) as daily corn consumption increased. Fat thickness and LD accretions for the stocking rate experiment both declined as SR increased (P<0.05), with the relationships being curvilinear for FT accretion and linear for LD accretion. Following a conversion of FT to an area, final fat percentage of final LD area showed a curvilinear decrease (P<0.05) as SR increased. Coefficients of determination (R2) were generally higher for the stocking rate experiment with the rye-ryegrass, which had less variation among breed types. Results of the study showed that real- time ultrasound technology can be used to determine responses of carcass- related traits to pre-feedlot treatments in grazing trials.