Abstract

Terminal sire crossbreeding systems which improve growth performance while maintaining parasite resistance have the potential to enhance the profitability of hair sheep enterprises. Katahdin (KT, n = 5), Suffolk (SU, n = 4), and Texel (TX, n = 5) rams were randomly mated to KT ewes over three years (Y1, Y2, Y3) at the Virginia Tech Southwest Agricultural Research and Extension Center. Post-lambing until weaning (80 d), pairs were managed on fescue pasture. At weaning, lambs (n = 242) were moved to an ungrazed pasture and provided a concentrate pellet daily for a 90 d grazing trial. During this time, body weight (BW), strongylid egg count (FEC), FAMACHA score and packed cell volume (PCV) were collected every 14 d. FAMACHA score ≥ 3 was utilized as the basis for anthelmintic treatment. Post-grazing, lambs were fed to approximately 50 kg BW. Lambs were harvested at the Virginia Tech Meat Center and carcass evaluation performed 1 d post-harvest. Statistical analyses were conducted using SAS with fixed effects of sire breed. No differences existed between sire breeds for adjusted number of lambs born or number of lambs weaned. At weaning, KT-sired lambs had lower BW than terminal sired lambs (P < 0.05). During the grazing trials, lnFEC, FAMACHA and PCV varied over time (P < 0.001) with lower FAMACHA scores for KT-sired lambs than SU- and TX-sired lambs (P < 0.05). Of the terminal sire breeds, TX-sired lambs had a greater FEC at deworming and required a greater number of days before treatment in Y2 (P < 0.05). At harvest, terminal-sired lambs were heavier than KT-sired lambs (P < 0.05) in Y1 while SU-sired lambs had greater BW than TX-sired lambs (P < 0.05) in Y2. Terminal-sired lambs had greater LM area and leg scores than KT-sired lambs (P = 0.05). These results indicate the potential of terminal sires (SU- and TX-sires) to improve lamb growth and carcass merit. Texel-sired lambs had more similar parasite resistance characteristics to KT-sired lambs and may have potential as terminal sires in forage based hair sheep production systems.

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