The effects of nematodiasis on weaner sheep in Western Victoria

Abstract

The development of nematodiasis and its subsequent effect upon production from Merino weaner sheep in western Victoria was studied at Hamilton during 1975-77. In each year, all weaners were drenched in summer and allocated to groups of 36, stocked at 15 sheep ha-1. The groups were given oral anthelmintics weekly, monthly or on five, two or one occasions between March and December of each year. A further two groups were not drenched, but one of these groups was given access to anthelmintic blocks. Nematodiasis was prevalent from the commencement of continuous pasture growth in autumn until early summer. Its effect varied considerably between both years and treatments. Undrenched sheep gained 39-66% less liveweight and grew 16-30% less wool than sheep drenched weekly. In two of the three years, liveweight gain and greasy fleece weight increased with frequency of anthelmintic treatment. The mean faecal egg count (EPG) in untreated sheep during the three years was over 500 eggs g-1 dry faeces and the mean number of nematode larvae ha-1 (LPH) was c. 1 x l06. Only those groups of sheep receiving 5, 12 or weekly drenches during the experimental periods had EPG or LPH that were significantly less than those of the undrenched sheep. Two to five anthelmintic treatments between March and December gave adequate control of nematodiasis.