Several topics relating to parasite life cycles need to be addressed to apply this knowledge in prevention and control programs. Seasonal Development of Infective Larvae Peak infective levels of larvae on contaminated pasture occur during late summer and fall. It may be most beneficial to use dewormers early in the grazing season to prevent escalation of the worm problem. Some parasites may overwinter on pastures. Thus deworming prior to the grazing season may not always provide desired levels of prevention.
Environmental factors leading to the highest level of infective larvae occur during summer and fall.
Pasture parasite control programs need to prevent these buildups and provide treatment of animals infested under these conditions. Periparturient rise This term is used to define the increase in worm egg production in ewes around lambing time. This situation occurs when, for reasons which remain unsolved, certain worm species undergo a period of arrested development in the animal. Then, at about lambing time, these parasites suddenly begin to mature. This characteristic, called hypobiosis, results in high numbers of worm eggs being shed into the environment which can heavily expose newborn lambs.