Economic losses attributed to internal parasites in cattle in Australia have been estimated at A$93.6 million per annum. The objectives of this study were to investigate chemical control strategies adopted by beef cattle producer, to ascertain the anthelmintics selected for use, and to evaluate the effectiveness of a summer anthelmintic treatment targeting inhibited O.ostertagi larvae.
A survey was developed to gather information on the control programs used, the anthelmintic used in these control programs and the delivery method of the anthelmintic. An interventional longitudinal study was designed to estimate the effect of an anthelmintic treatment targeting inhibited O.ostertagi larvae at the start of summer on growth rate of yearling heifers. The effectiveness of two laboratory tests (faecal worm egg count and serum pepsinogen) used to assist with the diagnosis of Ostertagiosis were evaluated.
One in four beef cattle producers followed a gastrointestinal parasite control program developed for the region. Of the producers using gastrointestinal parasite control, 89% relied on the macrocyclic lactone class of anthelmintic with 63% preferring a pour-on application. An anthelmintic treatment in early summer targeting inhibited O.ostertagi resulted in a substantial (66g/day) and significant increase in average daily weight per heifer (treated 344±0.0144g/d vs control 278±0.006g/d; P <0.001).
This study identified a reliance on the macrocyclic lactones class of anthelmintics, a preference for a pour-on delivery and a poor adoption of regional specific gastrointestinal programs. It showed a beneficial effect on the growth rate in yearling heifers treated with an injectable anthelmintic treatment targeting inhibited O.ostertagi larvae in early summer and highlighted the need to develop better tools to assist in the diagnosis of Ostertagiosis.