Ecology of the free-living stages of 'Haemonchus contortus' in a cool temperate environment

Abstract

Current understanding of the ecology of 'Haemonchus contortus' is incomplete and seen as an impediment to effective control of the worm in summer rainfall regions, where outbreaks are common and can result in significant stock mortality. Although there has been a wealth of published research on the effects of temperature on free-living development of 'H. contortus', our level of understanding of how moisture in the micro- and macro-environments influences development to infective larvae on herbage is considerably lower. The current state of knowledge of the free-living ecology of 'H. contortus' is reviewed in Chapter 2, with a particular focus on research findings since the 1970s. Knowledge gaps are highlighted, and a proposal made for a framework on which future investigations of 'H. contortus' can be based in order to improve prediction of free-living development. The key hypotheses under investigation in the experimental studies concerned the quantitative effects of moisture on free-living development of 'H. contortus', and are summarised in Chapter 1 and in further detail in each of the experimental chapters (Chapter 4-6). Plot experiments were conducted in the Northern Tablelands of NSW, where 'H. contortus' is the most important parasite of sheep. Subsequent laboratory experiments, designed in order to extend and explain the findings of the plot experiments, were conducted in programmable incubators in which temperature was regulated to mimic conditions typical to the Northern Tablelands summer. All experiments focused on testing the effects of a range of rainfall and moisture-related variables on 'H. contortus' development from egg through to infective larvae.