Oocysts of Eimeria in the litter of broilers reared to eight weeks of age before and after withdrawal of lasalocid or salinomycin.

Forty-six broiler houses were examined for the presence of oocysts of Eimeria in the litter before and after withdrawal of lasalocid or salinomycin from the feed. A decrease in number of small oocysts (Eimeria acervulina or Eimeria mitis) was observed following withdrawal of medication. Numbers of medium-sized oocysts (probably Eimeria tenella) remained the same, but an increase in large oocysts (Eimeria maxima) was recorded. No lesions attributable to Eimeria tenella were found in the ceca of birds after withdrawal of the drug. More small- and medium-sized oocysts were found at sites with new litter than at sites where the litter had been employed for previous flocks. No difference in the number of oocysts was found, whether birds were reared on oak shavings or a mixture of pine shavings and rice hulls. The number of oocysts was positively correlated with the moisture content of the litter, but there was no correlation between oocysts present and the final BW or feed conversion of the birds. Moisture levels were highest (after withdrawal of drug) for new litter or oak shavings. There was no correlation between moisture content of the litter and BW or feed conversion.