Epidemiology of gastrointestinal helminths in stationary and migratory sheep flocks in arid Rajasthan

To study the epidemiology of gastrointestinal (GI) parasites, 3872 faecal samples from 14 flocks (10 stationary and 4 migratory) of arid Rajasthan were evaluated at monthly interval. The monthly incidence of strongyle infection ranged from 35.2% (March) to 82.3% (July) in migratory and remained almost similar to stationary flocks during monsoon (July to October). The incidence of other GI nematodes was low in both the rearing systems. The monthly intensity of strongyle infection ranged significantly (p<0.001) from 77.4±11.5 (March) to 1202.5±183.0 epg (July) and from 10.3±2.0 (February) to 1188.9±139.7 epg (July) in migratory and stationary flocks, respectively. In migratory flocks relatively higher proportion of animals found to shed >1000 epg during September-October compared to stationary flocks. Generic composition of strongyle larvae exhibited predominance of Haemonchus contortus followed by Oesophagostomum spp. and Trichostrongylus spp. The incidence was higher in migratory flocks from October to March i.e. during migration and this could be attributed to travelling stress and en route exposure of flocks to contaminated pastures in semi-arid/irrigated area. During February-March the major source of grazing was post harvested fields in migratory route and this resulted in further decrease in FECs possibly as a consequence of absence of infection in post-harvested crop residues and occurrence of hypobiosis phenomenon. Unfavourable climatic conditions, possible onset of hypobiosis, failure of larval translation on pasture, denudation of grass cover/mat in grazing area, practices of grazing in harvested field or on top feeds resulted in significant decline in FEC from November onwards without any anthelmintic intervention. The flock performance remained almost similar in both the system of flock management. Thus, worm management programme based on interaction between epidemiology, weather and management of flocks resulted into reduction in drench frequency, reduced selection pressure in parasite population, extend life of existing anthelmintics and reduced the unwanted expenditure incurred by farmer on anthelmintic use.