Factors affecting the survival and migration of the free-living stages of gastrointestinal nematode parasites of cattle in central Queensland

Faecal pats containing parasitic nematode eggs were deposited monthly on worm-free pasture, from mid-1975 to early in 1979, near Rockhampton in central Queensland. Pasture samples were collected monthly from beside these pats and the number of infective larvae on the samples was counted. Cooperia spp. were the most numerous larvae on pasture all year round and Haemonchus placei were commonly present in low numbers. Small numbers of Oesophagostomum radiatum larvae were found, mostly during summer. Dung beetle activity and rainfall influenced larval populations on pasture, but temperature did not. Beetles were not active in winter, and pats deposited in spring, summer and autumn when beetles were active yielded only 42, 44 and 26%, respectively, as many larvae per 1000 eggs deposited as winter pats. Pats in which beetle activity was minimal (feeding only), moderate and intense (complete destruction), yielded 43, 10 and 6%, respectively, as many larvae per 1000 eggs as intact pats. Larval densities on pasture were highest after the first saturating rains during the spring-summer period and most of these larvae migrated from unattacked pats deposited in winter. Beetle numbers and activity increased with the summer rains and so few larvae were available to migrate onto pasture during late summer and autumn when the highest falls of rain were recorded. The regression of larval recovery on rainfall was positive and statistically significant when data collected soon after these very heavy rainfall periods were omitted from the analysis. In 1977, drought-breaking rains increased the normal larval density on pasture 10-fold because larvae in pats deposited in the last 4 months of the drought migrated onto pasture immediately after the rains. This work suggests that in summer rainfall areas where dung beetles are active, helminth control may be achieved by reducing the worm egg output from cattle during the winter.