Max R.A., Wakelin D., Dawson J.M., Kimambo A.E., Kassuku A.A., Mtenga L.A., Craigon J. and Buttery P.J. Effect of quebracho tannin on faecal egg counts, worm burdens and performance of temperate sheep with challenge nematode infections. Journal of Agricultural Science (2006) 143: 519-527. (DOI: 0.1017/S0021859605005691)