The production of developmental defects of enamel in the incisor teeth of penned sheep resulting from induced parasitism

Abstract

Thirty-four sheep were infected with nematode parasites (Trichostrongylus spp. and Ostertagia circumcincta) during central incisor formation. The tooth enamel was examined for defects of mineralization at eruption and compared with that of 14 control sheep. The type and number of parasites given, the duration of the infection and the age of the sheep were varied. Sheep receiving high doses of parasites e.g. 200,000 T. vitrinus + 20,000 O. circumcincta showed severe systemic effects (debilitation, scouring and weight loss) which were of short duration (7-10 days) as the infections were terminated by anthelmintic treatment. Hypoplastic enamel (a break in continuity) was induced in all 5 sheep infected at 8 1/4-9 months of age and demarcated opacities (an alteration in the translucency) in 3 out of 4 sheep infected at 10 months of age. Sheep given 150,000 or 40,000 T. colubriformis showed less obvious systemic effects although the weight loss continued in some sheep for up to 54 days. Although opacities of the enamel in the form of parallel lines, sometimes with localized increase in width or with a diffuse opacity superimposed, were seen by microscopic examination (X 10) of teeth in this group, many of the teeth from the control sheep showed similar lesions. Only the hypoplastic lesions can be attributed with confidence to the experimental manipulations.