Seasonal Variation in the Incidence of Gastro-intestinal Nematodes in Sheep in Iran

To record the seasonal variations in the incidence of gastro-intestinal nematodes of sheep around Shiraz, Fars Province of Iran, 1114 sheep in different age groups were examined. Adult sheep showed higher (P<0.05) infection (52.3%) as compared to young ones (38.17%) in all the seasons of the year. Infection was higher (P<0.05) in summer and spring seasons. Nematodes of 11 genera were recorded and Haemonchus sp., Marshallagia sp., Ostertagia sp. and Trichostrongylus spp. predominated in adult sheep while Nematodirus spp. were more common in young animals. Mixed infection with 2–6 different nematode spp. was common in both categories of animals but emergence of Marshallagia sp. as common parasite in adult sheep and lambs was interesting. High infection in all seasons, suggested their endemicity in the area and need effective control measures.