Responses of hair and wool sheep to a single fixed dose of infective larvae of Haemonchus contortus

Body weights, fecal egg counts (FEC), and packed cell volumes (PCV) of hair sheep and wool sheep crossbred lambs were compared over 8 weeks following administration of a single dose of approximately 10,000 third-stage larvae of Haemonchus contortus. Hair sheep lambs (n=17) were reciprocal crosses between mainland USA populations of Barbados Blackbelly (BB) and Virgin Islands White (VIW) sheep. Wool sheep lambs (n=64) were from a crossbred composite of 50% Dorset, 25% Rambouillet, and 25% Finnish Landrace breeding. Lambs of both breed types continued to grow during the period of infection. Mean weights were higher for wool lambs (39.7±0.8 kg) than for hair lambs (28.2±1.5 kg). FEC increased to week 5 in both breed groups and remained elevated in wool lambs through week 7 but declined sharply in hair lambs after week 5. Mean FEC for weeks 4 through 8 were 4011±361 eggs per gram of feces (epg) in wool lambs, and 1135±196 epg in hair lambs. PCV declined through week 7 in wool lambs but stabilized and then increased after week 4 in hair lambs. Mean PCV in weeks 4 through 8 were 22.4±0.3% in wool lambs and 24.3±0.5% in hair lambs. These results suggest that Caribbean hair breeds may be able to contribute significantly to development of parasite-resistant sheep populations.