The relation between the natural worm burden of steers and the faecal egg count differentiated to species.

The relation between the faecal egg count and the worm burden was investigated in 104 steers of three breeds, 9-24 months of age, which were subjected to natural infection with nematode larvae from pasture at The National Cattle Breeding Station near Rockhampton in central Queensland. The worm species found were Cooperia spp., Haemonchus placei, Trichostrongylus axei, Oesophagostomum radiatum and small numbers of Bunostumum phlebotumum. The faecal egg count was found to be a reliable measure of the size of the worm burden. Steers slaughtered at 24 months of age had 90% fewer worms and 96% fewer eggs g-1 faeces (P less than 0.001) than those slaughtered at 9 months of age. Adjusted for age, the estimated faecal egg count increased 14 times (95% confidence limits 7.2, 35) for each 10-fold increase in estimated worm numbers. The proportion of each species of larvae obtained from faecal culture (larval differential count) was related to the composition of the worm burden as measured by the proportion of worms in selected maturity categories and in selected length categories for each species (P less than 0.001).