Trichostrongylus colubriformis: relationship between ageing of infective larvae, infectivity and egg production by adult female worms.

Relationships between egg production and infectivity were studied with infective larvae of Trichostrongylus colubriformis which had been stored for up to 22 weeks at 24 degrees C. After different storage times, larvae were administered to lambs and the number of parasites which reached the adult stage was counted five weeks after infection. Egg production was estimated for the same batches of animals by performing a quantitative coproscopic examination from the third week of infection onwards. Infectivity was maximum and constant during the first six weeks of storage and then decreased regularly from the 9th week to the end of the experiment. However, the number of eggs produced per female worm was constant during the first 6 weeks then doubled and remained constant from the 9th to the 22nd week of storage.