DEVELOPMENT AND SURVIVAL OF INFECTIVE LARVAE OF NEMATODE PARASITES OFSHEEP ON PASTURE IN A COOL TROPICAL ENVIRONMENT

The development and survival of nematode parasites of sheep were studi ed in a cool tropical environment of the highlands of Ethiopia on 24 p lots serially contaminated with Haemonchus contortus, Longistrongylus elongata and Trichostrongylus colubriformis eggs over a period of 2 co nsecutive years from June 1993 to May 1995. The availability of infect ive larvae was monitored by monthly pasture sampling and larvae recove ry. Infective larvae were recovered from the herbage collected from th e plots contaminated in June, July, August, September and October of b oth years. The longevity of infective larvae varied between two and si x weeks when eggs were deposited on pasture in June and October, respe ctively. During the dry and short rainy season (November through May), eggs failed to develop into L-3 stage. It is suggested that the long period (7 to 8 months) of lack of development of trichostrongylid infe ctive larvae on the pasture can be efficiently used in a strategic tre atment programme to interrupt transmission of H. contortus, L. elongat a and T. colubriformis in sheep in this environment. (C) 1998 Elsevier Science B.V. All rights reserved.