2012 Annual Report 1a.Objectives (from AD-416): In a range sheep production environment, evaluate different biological types of sheep for reproductive efficiency, rate and efficiency of growth, carcass composition, meat quality, and mature size. Use quantitative genetic methods to identify physical and physiological criteria for enhancing reproductive efficiency and other economically important traits, including meat quality, quantity, and flavor. 1b.Approach (from AD-416): Reproductive efficiency, rate and efficiency of growth, carcass composition, meat quality, and mature size will be evaluated for different biological types of sheep in a range sheep production environment. New genetic information gained from these evaluations on traits affecting production efficiency, and the relationship of the traits to growth and carcass characteristics, will be used to develop new composite terminal sire lines. These sire lines will be used with appropriate maternal lines to meet target market specifications for commercial lambs and produce more desirable end products that meet consumer demands, without sacrificing reproductive efficiency. 3.Progress Report: This project involves characterization of sheep breeds and development of composite lines suitable for range environments. The U.S. sheep industry lacks paternal genetic lines that will enable the industry to adequately address current and future grower, feeder, packer, retailer, and consumer demands for market lambs and their byproducts. U.S. Sheep Experiment Station scientists and their collaborator at Virginia Tech University have analyzed a portion of the data collected during a 3-year study to characterize Columbia-, USMARC Composite-, Suffolk-, and Texel-sired F1 lambs for traits of survival, growth, feed efficiency, carcass composition, and meat quality. In 2012, four manuscripts were written. All four manuscripts were submitted to peer-reviewed scientific journals. Three of the manuscripts have been accepted for publication, and the fourth manuscript has been reviewed, edited, and returned to the journal for final consideration. The genetic information gained from this study has been used to initiate the development of a new composite (i.e., in this case, genetics from three breeds of sheep) terminal-sire genetic line of sheep. The initial breed crosses, with the planned proportion of each of the three founding breeds, were realized in 2010, and, as of 2012, approximately 1015 of the sheep have been produced and are under evaluation. This progress relates directly to Objective 1 and Objective 2 of the in-house project, "Evaluate different breeds and crosses as specialized paternal and maternal lines in an extensive western rangeland, terminal crossbreeding system", and , "Strategically manipulate management factors to increase the likelihood that a ewe will be productive at 18 months of age". We have substantially completed these objectives as a result of this research.