There are environmental factors to take into consideration when fighting the war against cocci. Extreme cold, freezing and heat wave conditions will go along way to keeping numbers down. Unfortunately spring , as it is here, is the time of year when conditions are perfect for them to ' go forth and multiply '
http://www.merckmanuals.com/vet/poultry/coccidiosis/overview_of_coccidiosis_in_poultry.html#v3340210
http://www.merckmanuals.com/vet/poultry/coccidiosis/overview_of_coccidiosis_in_poultry.html#v3340210