The Effect of Different Levels of Larval Intake on the Output of Eggs by Ostertagia Circumcincta in Lambs

Abstract

Groups consisting of six eight-week-old lambs were subjected to different infection regimens with Ostertagia circumcincta and the rate of faecal egg output was followed. Animals receiving 15 doses of 50 larvae followed by 30 doses of 2500 showed a similar faecal egg output to a group of lambs receiving only the second dose. Animals receiving 15 doses of 10 larvae showed a higher faecal egg count following the second infection than the group receiving only the second infection. The group which received 30 doses of 10 larvae followed by 30 doses of 2500 had a similar faecal egg count to the group of sheep receiving only the second infection. The group which received 30 doses of 50 larvae followed by 30 doses of 2500 larvae had a faecal egg count which was significantly lower than the group receiving only the second infection. Ten doses of 25 000 larvae given to all five of these groups produced no effect on their faecal egg output but in a sixth group of worm-free sheep the faecal egg output reached a peak of 4000 eggs/g. The significance of these results is discussed particularly in relation to the choice of grazing management regimes designed to reduce the effects of worm infections.