Weaned merino lambs, grazing pastures low in
selenium, were used to investigate the effect of
selenium status on immunity to trichostrongylids. Six weeks following
selenium supplementation to 14 of the 27 sheep using intraruminal
selenium pellets, 5000 Ostertagia circumcincta and 5000 Trichostrongylus colubriformis larvae were administered orally to all sheep. At four weeks after
infection, the mean total worm burden in the
selenium supplemented sheep (5537 +/- 343, n = 14) was not significantly different (P greater than 0.05) from that in the unsupplemented sheep (5614 +/- 374, n = 12) and faecal worm egg concentrations were also similar in the two treatment groups. At this time, mean red cell
glutathione peroxidase activities in the supplemented and unsupplemented groups were 430 and 11 U g-1 haemoglobin, respectively, and clinical
white muscle disease had been observed in the latter group. These results suggest that increasing
selenium status of
selenium deficient sheep by the use of intraruminal
selenium supplementation, has a negligible effect on resistance to an artificial challenge
infection of O circumcincta and T colubriformis.