Feedlot Performance and Carcass Characteristics of Lambs Sired by Texel, Romanov, St. Croix or Dorset Rams from Polypay and St. Croix Ewes

Over a 2-year period, crossbred lambs resulting from the mating of Texel (T), Romanov (R), and St. Croix (S) rams with Polypay (P) and S ewes, were finished during the summer and late fall to determine feedlot performance and carcass characteristics. A total of 175 wether lambs of the five genotypes (R x P, R x S, S x S, T x P and T x S) were fed a high-energy diet for an average of 110 d (Experiment 1). Purebred St. Croix lambs weighed less (P < 0.05) at the beginning and end of the finishing period, had the lowest average daily gain (ADG) (P < 0.05), and the lowest Gain:Feed (P < 0.10) of the five genotypes evaluated. All five genotypes produced carcasses with a quality grade ≥ Choice. In a subsequent 2-year experiment (Experiment 2), 251 lambs sired by either Dorset or St. Croix rams from the ewes created in Exp.1 were used. Dorset-sired lambs were heavier (P < 0.10) at the end of the feeding period and had greater ADG (P < 0.10) than lambs sired by St. Croix rams. Wether lambs were heavier (P < 0.10), grew faster (P < 0.10) and ate more (P<0.05) feed than female lambs. Lambs from crossbred ewes were heavier (P <0.05) at the beginning and end of the finishing period and grew faster (P < 0.10) than lambs from purebred St. Croix ewes. When Dorset rams were used as the terminal sire, lamb feedlot performance was similar among the five ewe genotypes used in this study.