Recovery of sheep lice (Damalinia ovis) from baled wool: A technique enabling nation-wide surveillance of louse ridden flocks

Abstract

Abstract Wool from pre-sale core samples was examined for sheep body lice. Wool was dissolved in boiling 20% NaOH, and the lice were collected by washing the treated sample over a 75 μm sieve. A total of 1112 samples from throughout New Zealand were processed. Six percent of these samples had more than 20 lice per 20 g of greasy wool, 3% had 16–20, 4% had 11–15, 9% had 6–10, and 78% had 5 or fewer lice per 20 g of greasy wool. The incidence of lice in baled wool was highest in the north of the North Island, and generally decreased from north to south. Samples gathered from 7 previous trials, for which the nocks' scoured wool yields had been recorded, were processed in a similar manner to determine the relationship between louse numbers and wool yield. There was a high correlation between louse numbers and loss in yield: 1 louse per g of greasy wool represented a loss of about 1%, 2 lice per g — about 4%, and 6 lice per g — about 5%. An estimate of the current annual louse-related loss of marketable fibre, based on the trial and survey data, is 0.2% of the national clip. The dissolution method we used could easily be adapted for routine louse surveillance.