The prevalence of coccidiosis in small and large scale poultry farms in Debre Zeit and comparison of the effect of management systems
Ort und Jahr der Promotion
In the planning of modern intensive poultry units very little attention is given to the effect ofsuch intensification on disease. Coccidiosis is an example of a major problem that has to bebrought under control before intensive production of poultry really can expand. The economiclosses due to coccidiosis are high and increases in the size of production units create conditionseven more favourable to the spread of coccidiosis. While peracute infections cause very heavymortality, morbidity due to latent and more insidious infections are not easily analysed, yet theyoften are of more grave significane from the economic stand point.Coccidiosis results from manifold interactions between agent factors (pathogenicity, endogenousreproduction, prepatent period) and host factors (age, immunity, genetical disposition).Management factors (housing, climate hygiene, feed) are of utmost importance, serving aspredisposing factors both in regards to the susceptibility of birds and the spread of infection.This investigation had the objective to establish baseline data on coccidia infections of chicken intwo different farms in Debre Zeit in Ethiopia and to assess the likely effects of management factorson infection intensity.The study was conducted from October to December 1996 in two study farms, Lemlem, a stateowned and managed poultry farm and Tsedey, a private farm.Representative faecal samples of houses of differently aged chicken were taken at two weeksintervals and numbers of oocysts (OPG) established. Post-mortem examinations were done on alldead chicken (total: 750) during the study period.OPG"s did increase with age of chicken from 200 at 1 week of age o maximum values of 300 (3weeks), 5500 (4.5 weeks) and 6700 (6 weeks) for houses 12, 1 1 and 10 in Lemlem, respectively.In Tsedey farm the highest OPG recorded was 6800.From the 518 autopsied at Lemlem farm, 245 showed lesions of coccidia infections. Of the 232 chickens at Tsedey 50 showed such lesions. This translated to prevalence of lesions in dead birds of 44.8% in Lemlem and 21.5% in Tsedey farm.Crude and coccidiosis proportional mortalities, calculated from farm records and post-mortem results were 78.0% and 37.7% in Lemlem and 25% and 18% in Tsedey, respectively.From the location of and kind of lesions it was inferred that E. tenella, E. acervulina and E. maxima with prevalences of 52.8%, 32.2% and 15.0%, respectively, were the dominant species involved in both farms. While keeping, management and feeding factors in both farms showed some deficits, the most striking difference was that in Lemlem farm birds of house 10 were subject to inadequate and suddenly changed feed rations, due to financial problems of the farm o purchase sufficient and adequate feed. No such problems were seen in Tsedey farm.It is inferred that such constraints in feeding in Lemlem did exert particular stress to the chicken, resulting in the unusually high (coccidia specific) mortality. High infections with coccidia spp. as such, as seen in Tsedey farm, were not accompanied by high mortality or other losses as long as birds were not subjected to sudden and unusual stresses.