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

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%.