Gastrointestinal parasite resistance is a heritable trait important to breeders of hair sheep. However, the U.S. Maternal Hair Index, provided by the National Sheep Improvement Program, omits parasite resistance. Selection indexes were designed in this study to continue improving total weight of lamb weaned per ewe lambing (TW), the current goal, and reduce postweaning fecal egg count (PFEC), an indicator of parasite resistance. These indexes placed varying emphasis on PFEC relative to TW. Annual genetic gains in TW and PFEC were predicted. Measurements for the traits used to construct the indexes were simulated to compare selection decisions—the number of rams and ewes chosen in common—between the current and the alternative indexes. Placing 79% of the selection emphasis on TW, and thereby 21% on PFEC, appeared preferable. With this balance, genetic gains in TW were reduced by only 2% relative to the current index, while PFEC was reduced favorably by as much as 8%. Additionally, over 60% of the males and 80% of the females were chosen in common between the current index and the proposed index including PFEC. Parasite resistance, therefore, can be incorporated as another selection criterion, with a positive impact on the productivity and fitness of hair sheep.

Read the full article in the Journal of Animal Science.