Some Relationships Between Trichostrongylid Infestation and Cobalt Status in Lambs * *—'Lambs' is used here to mean sheep in their first year. : Haemonchus Contortus Infestation † †—An abstract of this paper was presented at the First International Congress of Parasitology, Rome, 1964. Extracted from a thesis presented to Dublin University for the degree of Ph.D

SUMMARY An experiment is described in which 28 lambs reared under worm-free conditions were fed on a low cobalt diet. When the lambs were approximately nine months of age they were randomly divided into four groups, two of which were supplemented with cobalt. Four weeks later the lambs of one supplemented and of one non-supplemented group were given 70,000 H. contortus infective larvae. Though there was no growth response to cobalt administration, liver cobalt levels of non-supplemented lambs were in the range associated with cobalt deficiency. In the early stages of infestation, cobalt-supplemented lambs showed higher egg counts, more severe anaemia and a 43 per cent mortality compared with lambs whose low cobalt diet was not supplemented and in which there was no mortality. It is concluded that a low level of cobalt in the diet of the host is detrimental to H. contortus.