Importance of gastro-intestinal helminths in calves in Papua New Guinea.

Gastro-intestinal nematodes caused poor growth rates and high mortality in undrenched calves when weaning preceded the wet season. Cooperia punctata and Haemonchus placei were the dominant species throughout the year with worm burdens and pasture contamination being highest during the wet season and lowest in the dry season. Histotropic stages occurred throughout the year in weaner calves but with a clear peak during the wet season. The development of host resistance against the most important worm species generally followed the pattern described by others but a breakdown in resistance against Cooperia occurred amongst some calves during the wet season. The number of H. placei, together with Bunostomum phlebotomum, was sufficiently large in some calves to cause death. It is likely that the even larger burdens of C. punctata observed would have contributed to if not caused death.