Overberg Research Projects. IV. The development of resistance to Nematodirus in lambs and spontaneous cure of Teladorsagia in weaners

Abstract

Soon after 12-week old suckling lambs reached a peak infestation of Nematodirus resistance developed, worm burdens falling by 43,1-97,5% in 18 week and 11-month old sheep respectively. Both Teladorsagia (syn. Ostertagia) and Trichostrongylus reached a peak geometric mean (G) of 18 099 and 3 278 worms on 02 December 1987 in weaners 5-6 months old. Within 6 weeks--6 months of sheep grazing on safe pastures, spontaneous cure of Teladorsagia occurred, worm burdens falling by 77,3-98,7 % but not of Trichostrongylus which was only reduced by 34-40%.