Prior experience and response of chickens to a streptococcal infection

Streptococcus fecalis infection was diagnosed in a population of individually caged meat-type pullets. A retrospective analysis showed that the infection occurred in pullets fed ad libitum and not in those whose feed intake was restricted. Among the former, resistance as measured by changes in body weight and blood heterophils and lymphocytes was greater for those from which blood samples had been obtained than from those which had not been bled. These data are consistent with the hypothesis that handling and feeding programs can modify an individual's resistance to infectious agents. Moreover, these experiences do not have to be extreme; rather they may be consistent with routine production practices such as restricted feed intake and removal of blood for serological testing.