Feedlot performance and carcass characteristics of spring-born wethers finished and processed in the fall or spring

Seasonal availability of lamb in the Western United States contributes to a large fluctuation in lamb supply. However, alternatives to fall marketing may not be practical unless feedlot performance and carcass characteristics of older lambs finished in the spring is equal to or superior to fall finished lambs. Our objective was to evaluate feedlot performance and carcass characteristics of spring-born wether lambs that were either feedlot finished in the fall and slaughtered at 7-8 months of age, or feedlot finished in the spring and slaughtered at 14-15 months of age. April- and May-born whiteface wethers (n = 240) were used in a complete random design experiment with wethers finished on an 80% whole barley-based diet starting when they were either 5-6 months (FALL), or 12-13 months (SPRING) of age in October or May, respectively. Wethers were fed in outdoor pens with 12-pens/finishing trial, four lambs/pen, and six finishing trials (three fall and three spring) during a 3-year period. Feedlot response variables included BW, DMi, gain:feed ratios, ADG, and body composition. Carcass variables were body wall thickness, back fat, yield, and USDA quality grade. Year x treatment interactions were detected for all feedlot variables (P < 0.05), but not for carcass characteristics (P > 0.50). Intake, ADG, final BW (years 2 and 3 only), and body wall thickness were greater (P < 0.05) for SPRING than FALL wethers. Quality grade, yield, and fat thickness depth did not differ (P > 0.05) between FALL and SPRING finished lambs. Gain:feed ratio did not differ (P > 0.05) between FALL and SPRING wethers in year 1, but was greater (P < 0.05) for SPRING wethers in year 2, and lower (P < 0.05) for SPRING wethers in year 3. We concluded that older wethers finished on a barley diet and managed under conditions of our study perform better in the feedlot than younger lambs. Combining these results with previous work demonstrates that older lambs are similar in terms of tenderness and flavor as younger wethers, and older lambs finished in spring are a desirable commodity for the feedlot industry and the consumer. (c) 2005 Elsevier B.V. All rights reserved.