197 Utilization of Katahdin rams with lower fecal egg count estimated breeding values improves parasite resistance and fitness traits of progeny

Abstract

Abstract Genetic selection for internal parasite resistance in sheep is a valuable tool to mitigate effects of parasitism especially when significant within breed variability exists. To better understand the mechanism underpinning this variability, a divergent mating scheme was established. Katahdin rams (n = 4) were selected based on their estimated breeding value (EBV) for fecal egg count (FEC) and grouped as numerically high (HiFEC; n = 2) or low (LoFEC; n = 2). Rams were randomly mated to Katahdin ewes at the Southwest Virginia Agriculture Research and Extension Center. Lambs were born mid-March and managed as one group, then weaned in mid-June. Lambs were transported to the WVU Animal Sciences Farm where they were randomly allocated to four pens with even distribution of sire and sex. All lambs (n = 109) were infected with 10,000 H. contortus L3 and the infection persisted for 5 weeks. Weights, FEC, and packed cell volume (PCV) were collected weekly. Statistical analysis was performed using the Mixed Model procedure and repeated measures in SAS with fixed effects of sire group. Weaning FEC was numerically greater for HiFEC-sired lambs vs. LoFEC-sired lambs (2914 vs. 1821 eggs/g; respectively). However, death loss for HiFEC-sired lambs tended to be almost twice that of LoFEC-sired lambs (20% vs. 11%, P = 0.09; respectively). Weaning weights did not differ. Fecal egg count from the prepatent to patent period was greater in HiFEC vs. LoFEC-sired lambs (210 vs. 34 eggs/g; P = 0.05). Packed cell volume was numerically lower in HiFEC-sired lambs. There were no differences in post-weaning growth, ultrasound fat thickness, or loin depth in lambs from divergent sire groups. These data indicate that utilizing LoFEC EBV sires reduces FEC and improves disease resistance in progeny without affecting growth or carcass traits