Role of host and environment in mediating reduced gastrointestinal nematode infections in sheep due to intensive rotational grazing

• Published in: Veterinary parasitology 2012-03, Vol.184 (2-4), p.180-192
• Main Authors: Colvin, A.F., Walkden-Brown, S.W., Knox, M.R.
• Format: Article
• Language: English
• Subjects: Animals; Antibodies, Helminth - blood; Blood Cell Count; Body Weight; Environment; Feces - parasitology; Feeding Methods - veterinary; Female; Gastrointestinal Diseases - immunology; Gastrointestinal Diseases - veterinary; Grazing management; Haemonchus contortus; Hematocrit; Host-Parasite Interactions; Immunoglobulin G - blood; Larva; Male; Nematoda; Nematode Infections - immunology; Nematode Infections - veterinary; Parasite Egg Count; Resistance; Rotational grazing; Seasons; Sheep; Sheep Diseases - immunology; Sheep Diseases - parasitology; Sheep Diseases - pathology; Sheep–Nematode; Trichostrongylus
• ISSN: 0304-4017; 1873-2550
• DOI: 10.1016/j.vetpar.2011.08.027

We have previously reported marked reductions in faecal worm egg counts (WECs) and drenching frequency in sheep on an intensive rotational grazing system (IRG) in a cool temperate environment with summer-dominant rainfall. These experiments were designed to determine the role of the host and environmental factors in mediating this. The role of host factors was investigated by administering a fixed larval challenge in each of the 4 seasons of the year to groups of 20 young sheep on three different management systems, including IRG. This comprised a mixed larval challenge containing infective larvae of Haemonchus contortus and Trichostrongylus colubriformis 7 days after short-acting anthelmintic treatment. A range of measurements was then made up to day 35 post-challenge. The role of environmental factors was determined by assessing pasture infectivity in four seasons using faecal worm egg counts (WECs) and pooled faecal culture of worm-free tracer sheep. The management systems were high input (HI) with high fertiliser inputs high stocking rate and relatively long grazing periods; typical New England management system (TYP) with moderate fertiliser inputs and stocking rate and relatively long grazing periods and; Intensive rotational grazing (IRG) with moderate fertiliser inputs and stocking rate but very short (mean 5 days) grazing periods and long (mean 103 days) rest periods. IRG sheep had higher mean WEC at 28 and 35 days after fixed larval challenge than HI and TYP sheep in spring (IRG: 9500±1000; HI: 4000±1000; TYP: 7200±1000 eggs/g, P