Selection practices and evaluation of growth and composition in three lines of synthetic beef cattle

摘要: Data in the present study came from two separate beef cattle breeding projects at Iowa State University. set-I included growth and carcass information of progeny small, medium, large lines synthetic cattle. Progeny were bom during years 1978 through 1990 Rhodes McNay research farms. used to evaluate selection practices three lines, effects some crossbreeding parameters on traits, estimate genetic trends for traits. set-II serially measured live-animal traits collected over a 6-year period (1991 1996). Most data purebred Angus Simmental sires with known expected difference females previous project. was sex breed composition feedlot determine best strategy adjust constant age end point. The overall mean generation interval 4.11 years. When averaged by line, 1.82, 1.47, 1.28 generations made respectively. Mean actual sire index differentials per were, 1.28, -.47, .84o There significant (P .10). Heritability hot weight, dressing percentage, longissimus muscle area, fat thickness, percentage kidney, pelvic, heart small line .30, .09, .21, .34, .15, respective values medium .52, .35, .33, .29, .07. order .31,. 18,. 17, .31, .18,