Rate and course of sporulation of oocysts of Eimeria acervulina under different environmental conditions

An experiment was conducted to determine the rate and maximum percentage of sporulation of Eimeria acervulina oocysts at various environmental conditions relating to temperature (21 versus 33 °C) and relative humidity (RH) (40 versus 80%). Measurements were made during 44 h after excretion of oocysts in 3 substrates: dry litter, clammy litter and pure faeces respectively. Maximum sporulation percentage in both dry (22.6%) and clammy litter (19.5%) was higher (P < 0.005) than in pure faeces (11.6%). Neither temperature nor RH had a significant influence on percentage of oocysts that sporulated. Under these simulated practical conditions approximately 25% of all oocysts sporulated, whereas sporulation under optimal conditions (29 °C, aeration, 2% K₂Cr₂O₇) showed a higher (68%) sporulation ability of oocysts. At 33 °C sporulation proceeded at a faster pace than at 21 °C (P < 0.005). With respect to RH and substrate, once sporulation started, the rate of increase to maximum percentage was not different. Time of onset of sporulation was influenced by temperature (P < 0.0001) and RH (P < 0.001). Time of onset occurred 15 h later at 21 °C compared with 33 °C and 5 h later at 40% RH compared with 80%. Also, an interaction effect (P < 0.01) was found with effect of RH being stronger at 21 °C compared with 33 °C. It was concluded that the most important aspect in the epidemiology of E. acervulina during a flock cycle is the time of onset of sporulation with temperature being the most important factor.