Effect of Mercury-Dominated Heavy-Metal Emission on the Course of Pasture Helminthoses in Sheep

Veterinarni Medicina 40, 1995, 11-15

A group of 30 improved Valashka sheep, grazed in submontane pastures 3 and 6 km far from the emission source of mercury-dominated heavy metals (L1 and L2) and in pasture situated out of mercury emission fall-out (K), were investigated for the prevalence and mean intensity of pasture helminth infection. Hg concentration in the grass stand was determined by the distance of emission source. The amount of mercury was increasing in the direction from control locality to locality 1, lying 3 km from the emission source. With the mean concentration of 4.298 mg Hg/kg in grass stand, 0.346 mg Hg/kg in the liver, 0.591 mg Hg/kg in the kidneys and 0.030 mg Hg/kg in the muscles (Tab. I) a high prevalence of pasture helminths was recorded in sheep. This prevalence was increasing in the direction from control locality to the nearest emission source (Tab. II). The only exception was Moniezia spp. and Strongyloides papillosus, with values at locality 2 being lower than those at control locality. Trichostrongylus spp. and Cooperia spp. were equally prevalent at all the localities studied. Mean infection intensity (Tab. III) showed an increasing tendency from control locality towards locality 1. Only Dicrocoelium dentriticum and Strongyloides papillosus were an exception, with the highest mean infection intensity recorded at locality 2 (5.3 and 3.3 specimens, respectively). The highest mean intensity at control locality was recorded for Cooperia spp. infection (4.5 specimens). Mean infection intensity at locality 2 (6 km from emission source) and control locality showed proximate values in Moniezia spp. (1.3-1.2 specimens), Nematodirus spp. (2.6-2.4 specimens) and Cooperia spp. (4.0-4.5 specimens). The highest differences in mean infection intensity between locality 1 and control locality were recorded in Trichostrongylus spp. (24.3-13.3 specimens), Ostertagia spp. (15.4-7.4 specimens) and Nematodirus spp. (5.1-2.4 specimens). With high values of mercury in pasture, grass grazing animals cumulate mercury in their organisms, mainly in the parenchymatous organs (liver, kidneys). Consequently, the immunity of animal organism is impaired, which is manifested by an increased prevalence and mean infection intensity of most pasture helminths

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