Pathological Changes and Vitamin B12 Metabolism in Sheep Parasitised by Haemonchus contortus, Ostertagia spp. and Trichostrongylus colubriformis

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Abstract
Groups of helminth-free weaner sheep were equilibrated on a ration containing almost no cobalt for 3 months. Cobalt supplementation was given orally thrice weekly to provide the minimum requirement for sheep. Infective larvae of Haemonchus contortus, Trichostrongylus colubriformis and Ostertagia spp. were given at two dosage levels to each of three groups, respectively, for 18 days, followed after a lapse of 30 days by small daily dosings of a mixed suspension of these helminths. Serum vitamin B12 was determined for a month before parasitization and for up to 12 weeks thereafter for every sheep. Sheep parasitized with higher numbers of T. colubriformis and Ostertagia spp. were significantly affected with loss of weight and in three cases, death, although there were no changes in the serum levels of vitamin B12 which remained fairly constantly at the lower end of the normal range during most of the parasitic stage. Sheep dying from these infestations showed terminal rises of serum vitamin B12 whilst those surviving showed falls in the last few weeks of the trial associated with significant decreases in liver cobalt levels. Morphological changes of some severity were found in the abomasum and intestines of the sheep receiving T. colubriformis and Ostertagia spp. and appeared to limit the uptake of vitamin B12. It is concluded that mild to moderate infestations of intestinal trichostrongyles and to a lesser degree Ostertagia spp. will interfere with the absorption of vitamin B12 and that these helminths may precipitate cobalt deficiency syndromes if cobalt is at or near the critical level in the feed.