Comparison of new composite breeds with the Suffolk breed as terminal sires in an extensive production system: carcass characteristics

Crossbreeding can provide the U.S. sheep industry with improvements needed to be competitive in the global protein market (Leymaster, 2002). Mating terminal sire breeds with excellent carcass characteristics to wool-type maternal breeds can add value despite fluctuating markets that are influenced by seasonality of production, import volume, and a variation in supply and demand (NRC, 2008). Evaluations of multiple terminal sire breeds suited for improving carcass traits in crossbred lambs reared in a rangeland system have been investigated at the U.S. Sheep Experiment Station (USSES). Initial results indicated Suffolk-sire crossbred lambs excel in many growth and carcass traits, but no single breed excelled in all carcass traits measured (Mousel et al., 2012; Notter et al., 2014). At present, the U.S. sheep industry and USSES developed terminal-sire composite (TSC) breeds for evaluation. Initially, an industry composite (Siremax) was developed from Hampshire, Suffolk, Columbia, and Texel breeds with focus on structural soundness, longevity, and lean growth. More recently, the Suffolk, Columbia, and Texel breeds were used to develop the USSES TSC breed, with selection emphasis placed on lamb survival, growth, efficiency, and carcass traits. To date, the TSC and Siremax breeds have not been compared with breeds traditionally used as terminal sires (e.g., Suffolk) in western U.S. range production systems. We hypothesized that the composite breeds would produce crossbred lambs with similar consistency and yield of carcass characteristics as Suffolk-sired crossbred lambs. The objective of this study was to compare the carcass characteristics of lambs produced by the TSC, Siremax composite, and Suffolk rams, when used as terminal sires mated to range-type ewes. The results described herein are the carcass component of a 3-yr study with a broader focus of comparison, including lamb survival, growth, efficiency, and retail traits.