Dr. Abebe Wosene, Dr. Ph. JacquietRAHMETO, ABEBE2020-06-122023-11-082020-06-122023-11-082005-06http://etd.aau.edu.et/handle/123456789/21536A cross-sectional study was undertaken from September 2004 to March 2005 on selected 40 dairy farms located in Central Ethiopia to determine the prevalence and species of the major protozoal causes of calf diarrhea, and the factors associated with their occurrence. Fecal samples were collected once from a total of 580 calves 0-345 days old and examined for the oocysts of Cryptosporidium and Eimeria spp. by centrifugal fecal flotation technique using concentrated sucrose solution. Accordingly, an overall point prevalence of 17.6% and 68.1% was recorded for Cryptosporidium and Eimeria spp., respectively. Of the 40 dairies sampled, 26 (65%) had one or more calves shedding Cryptosporidium oocysts whereas all of the farms had calves shedding Eimeria oocysts. In this study the species of Cryptosporidium circulating in the farms was presumed to be Cryptosporidium andersoni (formerly known as Cryptosporidium muris) based on morphology of the oocysts and certain epidemiological features of the parasite. With regard to the species of Eimeria, a total of 11 species were identified namely Eimeria bovis, Eimeria zuernii, Eimeria auburnensis, Eimeria canadensis, Eimeria ellipsoidalis, Eimeria subspherica, Eimeria cylindrica, Eimeria alabamensis, Eimeria wyomingensis, Eimeria bukidnonensis, and Eimeria brasilensis in descending order of their relative prevalence. Neither Cryptosporidium nor Eimeria spp. were found to be statistically associated with diarrhea (P>0.05). Both parasites were detected in a wide age range of calves: Cryptosporidium in 21-345-day old calves and Eimeria spp. in 15-345-day old calves. Among the risk factors studied, the frequency of cleaning the calf rearing houses was the most important factor associated with the likelihood of infection with Cryptosporidium spp. whereas geographical zone where samples were taken from and age of the calves were the most important factors associated with the likelihood of infection with Eimeria spp. The mean and maximum Eimeria oocysts per gram of feces (OPG) determined by using McMaster technique was 5109 and 267,000, respectively. There was a strong association between OPG and age of the calves (P<0.001) and consistency of the feces (P<0.001), the mean OPG was significantly higher in younger and diarrheic calves.enCalf diarrheaCryptosporidiumEimeriaPrevalenceRisk factorsThesis