Rate and course of sporulation of oocysts ofEimeria acervulinaunder different environmental conditions

Abstract

Summary: An experiment was conducted to determine the rate and maximum percentage of sporulation ofEimeria acervulinaoocysts 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 ofE. acervulinaduring a flock cycle is the time of onset of sporulation with temperature being the most important factor.