Abstract

The incidence of flystrike in New Zealand flocks is about 3% in most years. This low level of prevalence makes it difficult to discriminate between potential flock replacements based on naturally occurring flystrike. Selection decisions could be improved if either the rate of flystrike could be raised artificially or an easily measured trait that has a higher level of occurrence could be found. The second approach is used in Australia where fleece-rot has both a higher incidence rate than flystrike and is highly genetically correlated to susceptibility to flystrike. However, the incidence of fleece-rot in New Zealand dual-purpose sheep is not sufficiently high to allow its use as an indirect indicator. In a effort to find a means of artificially increasing the incidence of flystrike, groups of hoggets were brought indoors and exposed to the Australian green fly Lucilia cuprina. In total, 5 trials (10 animals/treatment) were run to compare: the susceptibility of Romney vs Perendale sheep, using wetting, dung or homogenised liver as attractants. Wetting was applied along the back from a watering can while the other attractants were applied to a patch on the shoulder, mid-back and rump. About 2000 gravid flies were released into a fly-proof room along with the penned sheep. The main results of these trials were: a) It was very difficult to get an established maggot population on clean wet sheep; few eggs were laid and no cases of established strike occurred; b) Dung acted as a moderately successful attractant; maggots were hatched on the sheep but none developed to the skin penetrating stage; c) Liver acted as a very successful attractant and maggots developed on all treated sheep. No between-breed differences occurred with wetting, dung or liver attractants. Further studies are required to refine the use of attractants. In particular, an attractant that is less powerful than homogenised liver but more potent than wetting or dung is required before moving onto large-scale field trials.

GL, Blackwell, MA Potter, YH Cottam, and HT Blair

Proceedings of the New Zealand Society of Animal Production, Volume 57, , 37-40, 1997