A study of the effect of gastrointestinal parasitism on physiological responses and food utilization in lactating sheep at pasture

Abstract

The effect of daily intake of Ostertagia circumcincta larvae on the performance of lactating sheep (Coopworth) on fresh herbage was investigated. The value of anthelmintic (Thiabendazole) treatment every 14 days in restoring or improving the performance of continuously infected sheep was also determined. Three groups of twin rearing ewes were formed within 4 weeks of parturition:- group (I) infected daily with 4000 larvae of O. circumcincta for 6 weeks, a further group (ID) was infected but treated with anthelmintic every 14 days and a third group (C) acted as the control. During the 6 weeks of the trial, all groups grazed together in the same paddock, using a 10 day rotation to prevent autoinfection.

The results suggest that O. circumcincta infection can impair the productivity of the breeding sheep and reduce lamb growth. Worm eggs in the faeces in group I were detected after 4 weeks of larval administration. Plasma pepsinogen concentration rose only slowly and after 4 weeks of infection. The reason for delay in both faecal egg counts and elevation of plasma pepsinogen concentration compared with other studies was discussed.

Over the whole trial, food intake, body weight, milk production and wool growth in group I were reduced by 12, 2, 8 and 13%, respectively, compared with group C. Growth rates of lambs reared by group C and I sheep were reduced significantly by 9 and 13%, respectively, compared with lambs reared by 10 sheep. It was suggested that these differences in lamb growth rates reflected the differences in milk production of their dams.

In general, similar performance was observed in both control and 10 groups, though for some parameters group 10 performed better than group C. Therefore, it was suggested that an additional control group would be needed to obtain an absolute measure of the real effect of anthelmintic treatment.