Grazing Treatment Effects on Ultrasound Measures of 12th to 13th Rib Fat Thickness and Longissimus Area11Names are necessary to report factually on available data; however, the USDA does not guarantee or warrant the standard of the product, and the use of the name by the USDA implies no approval of the product to the exclusion of others that may be suitable.
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2002 American Registry of Professional Animal Scientists The management of cattle backgrounded on pasture for the feedlot could have residual effects on eventual carcass characteristics, but it is not known if variation of ultrasound measures is sufficiently low to determine grazing treatment effects. Yearling steers were ultrasonically scanned at the start and finish of two grazing experiments to determine whether 12th to 13th rib fat thickness (FT) and longissimus area (LA) could be estimated with ultrasound to determine treatment effects on these measures and to evaluate trends in the measurements over a range of ADG. One grazing trial was conducted with bermudagrass [Cynodon dactylon (L.) Pers.] using yearling steers to evaluate the effects of increasing levels of corn supplementation (CS; 0, 0.5, 1.4, and 2.3 kg/d per steer) on ADG. The second trial was conducted with a Maton'rye (Secale Cereale L.) and TAM90 ryegrass (Lolium multiflorum L.) mixture to determine effects of stocking rate (SR; 3.7, 5.2, and 6.7 steers/ha) on ADG. For the CS study, there were linear increases in FT (P<0.10) and LA (P<0.001) as corn consumption increased. For the SR experiment, FT decreased nonlinearly (P<0.05), and LA declined linearly (P<0.001), as SR increased. Longissimus area in both experiments increased linearly (P<0.05) as ADG increased. Fat thickness increased linearly (P<0.001) over the range of ADG measured in the CS experiment, but increased nonlinearly (P<0.01) over the range of ADG obtained in the SR experiment. Results indicated that ultrasound technology can be used to determine grazing treatment effects on FT and LA measurements.