Studies relating to the effects of environment and behaviour on certain diseases of sheep in the Goondiwindi district : with particular reference to haemonchosis

Abstract

The studies described in this dissertation had as an objective, the clarification of the affects of environment and grazing behaviour on the incidence of certain diseases of sheep, namely haemonchosis, posthitis, mycotic dermatitis and cutaneous myiasis. Although the investigation was conducted in the Goondiwindi district of south-eastern Queensland, the findings could have a much wider application. A study of the epizootiology of haemonchosis was continued from March, 1961 to June, 1964, during which time monthly faecal egg counts were recorded and fluctuations in counts were related to environmental factors. Also previous studies on the epizootiology of haemonchosis in the Goondiwindi district are reviewed, and the life-cycle of Haemonchus contortus is described. The present study showed that the haemonchus season in most years occurred between September and April. Bioclimatographs for 1961, 1962, 1963 and the average value of 30 years, indicated an association between the activity of H. contortus and the mean monthly minimum temperature of 50°F. The use of a mean monthly minimum temperature of 50°F as an indication of the onset of the haemonchus season was found to be more reliable than the use of a mean monthly maximum temperature of 63.9°F as suggested by Gordon (1948). As Gordon's hypothesis was based on a study of haemonchosis at Armidale, New South Wales, meteorological data for Goondiwindi and Armidale were compared in an effort to reconcile differences between Gordon's findings and those of the present study. The environments of Goondiwindi and Armidale were shown to differ appreciably and it was suggested that the use of temperature records to forecast seasonal activity of H. contortus may be used as follows: In environments such as Armidale with a narrow diurnal temperature range and relatively low maximum temperatures, the use of the mean maximum temperature may be the best criterion. On the other hand, in environments such as Goondiwindi where there is a wide diurnal temperature range and high maximum temperatures, the use of the mean minimum temperature is more reliable than the mean maximum temperature.