Genetic selection for internal parasite resistance in sheep is a valuable tool to mitigate effects of parasitism, especially when significant within breed variation exists. Towards this objective, West Virginia University (WVU) and Virginia Tech researchers devised a divergent mating scheme using Katahdin rams selected for high or low estimated breeding values (EBVs) for fecal egg count (FEC).
High FEC EBV (n=2) and low FEC EBV (n=2) rams were randomly mated to Katahdin ewes at Virginia Tech's Southwest Virginia Agriculture Research & Extension Center. Lambs were born in mid-March and weaned in mid-June. They were exposed to parasites during the pre-weaning phase. After weaning, the lambs were transported to WVU's animal science research farm where they were put in pens. All lambs (n=109) were experimentally infected with 10,000 Haemonchus contortus L3 (larvae). Infections persisted for five weeks. Data were collected weekly.
Numerically, weaning FEC was higher in the lambs sired by rams with high FEC EBV than lambs sired by rams with low FEC EBV (2914 vs. 1821 epg). Fecal egg counts from the prepatent to patent period were greater in the high FEC EBV sired lambs (210 vs. 34 epg). Death loss was higher for lambs sired by high FEC EBV rams (20 vs. 11%). Packed cell volume (PCV) was numerically lower in high FEC EBV-sired lambs. Among the divergent sire groups, there were no differences in weaning weights and post-weaning growth or carcass traits, as determined by ultrasound.
The results showed that rams with low FEC EBVs sire lambs with lower fecal egg counts and vice Selection for parasite resistance did not have any negative effects on growth or carcass traits. It may improve disease resistance.
Source: Abstract, Annual meeting of the Southern Section of the American Society of Animal Science; Oklahoma City, Oklahoma; January 2019