EPIDEMIOLOGY OF GASTROINTESTINAL NEMATODES OF SHEEP IN WET TROPICAL CONDITIONS IN MALAYSIA

A study on the seasonal variations in the population structure of Haem onchus contortus and Trichostronglyus colubriformis was conducted for a period of 12 months in a typical large scale sheep farm on improved pasture in Peninsular Malaysia which has a wet tropical climate. Succe ssive groups of helminth-free tracer lambs were grazed for 4 weeks tog ether with naturally infected sheep and were necropised for worm count s 2 weeks after their removal from the pasture. The monthly population s of H. contortus fluctuated slightly except in May and August during which more worms were found in the tracer animals. The numbers of T. c olubriformis were comparatively high from October to December 1992 and again in March 1993, low during April and June 1992. Small numbers of hypobiotic larvae of H. contortus were detected in the tracer animals . Development and survival of infective larvae of H. contortus and T. colubriformis on pasture were investigated by spreading faeces contain ing eggs on grass plots in October 1993, February and May 1994. Develo pment of the eggs to the infective larvae occur red within one week an d their survival, times were 7 weeks in the 3 experiments. The potenti al for control by rotational grazing is discussed.