Effects of toltrazuril on the growth of piglets in herds without clinical isosporosis.

Isospora suis is a widely prevalent and economically important parasite. The antiprotozoal compound, toltrazuril, was given as a single treatment to piglets without clinical signs in 10 herds. The daily weight gain (DWG) and mortality between the treatment date and weaning was compared on each herd in 10 treated and 10 control litters. The faeces of control litters were examined for oocyst excretion. In six herds, no oocysts were detected and treatment had no effect on DWG or mortality. In four pig herds, oocysts were detected and toltrazuril treatment significantly improved DWG by 25 g (P=0.003). Mortality rate was not affected. The partial economic benefit of toltrazuril treatment in positive herds was 0.20 euros per piglet. A single toltrazuril treatment of piglets in herds without clinical signs of isosporosis but with oocysts detected significantly improved DWG and was considered economically justified on each farm.