106 Effect of Sire Breed on Gain, Carcass Characteristics and Parasite Resistance of Katahdin Crossbred Feedlot-Finished Lambs: Year 2

Abstract

Improvement of carcass merit while maintaining parasite resistance is critical to retain profitability in Katahdin sheep. In year 2 of this study different Katahdin (KT), Suffolk and Texel (TX) sires were used to mate Katahdin ewes. Lambs were born and raised in confinement until weaning, then shipped to the West Virginia University Animal Science Farm. Lambs were transitioned onto a complete pellet (16% CP) and were fed ad lib throughout the study. After transition all lambs (n = 7 KT, 13 SU, 11 TX) were infected with 10,000 Haemonchus contortus larvae and weight, blood and fecal samples were collected weekly for the duration. After 5 wk all lambs were treated with levamisole (8mg/kg) and lambs were challenge infected 3 wk later with 10,000 H. contortus larvae. Ultrasonic determination of REA and fat depth occurred 1 wk prior to the end of the 77 d study. Upon study completion 5 lambs from each sire group were randomly selected for carcass analysis at the Virginia Tech Meats Laboratory. Analysis of parasitological data indicated no effect of sire during the primary infection however sire effects were observed during challenge infection as SU-sired lambs had a greater fecal egg count (FEC) (269 eggs/g) compared to KT-sired lambs (116 eggs/g; P = 0.04) whereas FEC of TX-sired lambs was not different from either sire group (170 eggs/g) P > 0.05. Upon slaughter no differences in worm burden of representative sire groups were observed. No significant differences were found in growth data between the sire groups, however, SU-sired lambs tended to have higher ADG (0.34 kg/d) vs. KT (0.25 kg/d; P = 0.051) but no advantage compared to TX-sired lambs (0.28 kg/d). Analysis of REA using ultrasound and direct carcass measurements revealed no sire effect (SU 15.19 cm2; TX 14.91 cm2, KT 12.71 cm2; P > 0.05). Leg score favored SU (11.6) and TX (11.2) lambs vs. KT-sired lambs (10.4) P < 0.05. A consistent trend can be observed across years, however there is a significant amount of sire variation which has the potential to impact performance of Katahdin crossbred lambs. These data indicate a need to further evaluate variation within the Texel breed to better identify superior rams.