An Epidemiological Investigation into Coccidiosis and Drug Resistance in Broiler Chickens

SummaryTo avoid economic losses arising from the emergence of resistant strains, detection of the decline in activity of the anticoccidial drug in use is essential. A method is proposed based on the correlation between economic performance and the number of excreted oocysts in the fresh faeces of four week old chickens. Fresh faeces samples were taken from 608 flocks of broilers in 17 commercial companies.The relationship or correlation between the five variables (weight, age, food conversion, viability and daily weight gain) which defined a flock of broilers and the influence of management, density of birds per m2, anticoccidial drug used and number of oocysts found in the faeces was examined by a factorial analysis.This study showed that the number of oocysts in 1 g of fresh faeces taken at four weeks of age is a useful indication of the risk of reduced economic performance. When resistance to a particular product is noticed in a poultry house, it is rarely an only case and clinical coccidiosis generally appears in all houses receiving the same drug.