Direct and indirect anthelmintic effects of condensed tannins in sheep

Anthelmintic activity of condensed tannins (CT) was evaluated both in vitro and in vivo. In vitro tests included egg hatch test and paralysis/mortality assay on adult Haemonchus contortus. In vivo anthelmintic effect was determined by faecal egg count reduction test in lambs. To this end, 18 lambs were divided into three groups (low tannin, high tannin and control). The lambs of low and high tannin groups were fed diets containing 2 and 3% CT while the control group was fed on diets without CT. In vitro trials showed a dose-dependent inhibition of nematode egg hatching; whereas, there was no effect of CT on adult H. contortus. In vivo trials indicated reduction in faecal egg counts in lambs fed diets containing CT. Feed intake and nutrient digestibility of CT-fed sheep was lower and nitrogen balance was higher as compared to control. Maximum weight gain was observed in animals fed diets containing 3% CT. The direct anthelmintic effect of CT, therefore, was evidenced by inhibited egg hatching; whereas, faecal egg counts reduction in sheep was through improved nutrient utilization.