Influence of coccidiosis on growth rate and feed conversion in broilers after experimental infections with Eimeria acervulina and Eimeria maxima.

Under experimental conditions, the effects of subclinical Eimeria (E.) acervulina and E. maxima infections on growth and feed conversion in broilers of different ages were analysed. It was concluded that infection with E. acervulina and E. maxima led to a process which was independent of the age at which the birds were infected. The infection adversely affected growth and feed conversion for 2 to 3 weeks, followed by a recovery period of 2 to 3 weeks when compensatory growth took place. From this study it may be concluded that subclinical coccidiosis in the first weeks of life and in the last week of life of broilers does not lead to appreciable damage on growth and feed conversion. Since coccidiosis cannot be avoided in practice, systems in which broilers contact subclinical coccidiosis either in the first weeks of life or in the last week of life should be aimed for. It is suggested that in a coccidiostat programme an efficient anticoccidiosis agent is particularly desirable in the 3rd and 2nd week before slaughter. Examinations performed one week or less before slaughter can hardly be justified, on the grounds that there is a risk of a negative effect on growth an feed conversion due to subclinical coccidiosis.

[Analysis of losses due to subclinical small intestinal coccidiosis caused by Eimeria acervulina and Eimeria maxima under field conditions]. / Een analyse van de schade van subklinische dunne darm coccidiosis veroorzaakt door Eimeria acervulina en Eimeria maxima onder praktijkomstandigheden.

Subclinical coccidiosis of broiler chickens caused by Eimeria (E.) acervulina and E. maxima results in a negative effect on feed conversion and retardation of growth. In the present report investigations in 80 broiler flocks are described in which the relationship between age of infection and economic effects were analysed under field conditions. Under these conditions, infections with E. acervulina and E. maxima were found to have a negative effect on growth and feed conversion, that this negative effect persists and accumulates for approximately three weeks following infection, and is subsequently completely or partly compensated for by increased growth rates. In the present study it was established that the losses due to subclinical coccidiosis of the small intestine in the 80 flocks investigated amounted to 6.4 cents per chicken under conditions occurring in the Netherlands. Ionophorous coccidiostats did not prevent infection with E. acervulina and E. maxima but did prevent infections with E. brunetti, E. necatrix and E. tenella.