Abstract
Abstract Improvements in growth and carcass conformation through terminal sire crossbreeding systems may improve lamb value in a pasture-based system. Therefore, the aim of this study was to compare the effects of different terminal sires on parasitism, growth, composition, and marketability of grazing lambs. Suffolk (SU; n = 2) and Texel (TX; n = 2) sires were mated to commercial ewes at the WVU Organic Farm. April-born lambs were managed on pasture as one group until weaning in midJune, then were separated into 3 replicates per sire breed. Lambs were rotationally grazed for 93 d with paddock movement every 10 d. Lambs were supplemented at a rate of 2% of bodyweight with a 16% CP corn-soybean meal supplement. Weights were collected at weaning and then weekly for the duration of the study. Fecal egg counts (FEC) and FAMACHA scores were collected biweekly. Lambs were de-wormed when FAMACHA score was ≥ 3. Ultrasound measures of rib eye area (REA) were obtained at study conclusion and lambs were marketed at a graded auction. Sire breed did not impact weaning weight or growth rate throughout the test. Fecal egg count was slightly higher in TX vs. SU-sired lambs (257 vs 191 eggs/g; P < 0.05). FAMACHA scores were lower in TX vs. SU-sired lambs (1.58 vs. 1.96; P < 0.0001). Fewer deworming treatments were necessary in TX-sired lambs at 10% (4/39) whereas as SU-sired lambs required 55% (22/40) (P < 0.0001). TX-sired lambs had greater REA (11.57 vs 9.42 cm2; P < 0.0001) and graded better at the saleyard. Grading was set to a 6 pt scale with higher equating to higher sale price. Lambs sired by TX rams graded 5.2 and SU-sired lambs graded 3.6 (P < 0.0001). These data demonstrate that Texel-sired lambs required fewer dewormer treatments and were compositionally more desirable when marketed
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