Age as a Factor in the Development of Resistance of the Chicken to the Effects of the Protozoan Parasite, Eimeria tenella

Abstract

C. E. HOLMES Department of Poultry Husbandry, University of Wisconsin Age has for many years been recognized as an important factor in the resistance of animals to the development and effects of their parasites. The work of Ransom (I92I) showed that young chickens were quite susceptible to infection with Syngamus trachea and were seriously affected by the infection whereas older chickens were refractory to infection. Herrick (1925) showed that the chicken became increasingly a more unsuitable host for the development of Ascaridia lineata as it increased in age. Johnson (I923) was of the opinion that age was an important factor in the resistance of chickens to coccidiosis and in his later work (I928) states, Young fowls infected with a large number for the first infection regularly die with the disease. This is more especially true of growing stock. Older fowls may show considerable bleeding and recover. . .. Tyzzer (I932) infected chickens with E. tenella when 6, 33, 50, and 7I days old. The resultant mortality was respectively 50, 37.5, 5o, and 100 per cent. He explained the greater susceptibility of the older chickens on a mechanical rather than a humoral basis. Mayhew (I934) concludes from his work that age is not a factor in the development of resistance of chickens to coccidiosis. Stafseth (193I) pointed out that older chickens were infectable but were more resistant to the effects of the parasites than were younger chickens. Many references might be cited, but from these studies there is evidently a difference of opinion regarding the importance of age as a factor in the resistance of the chicken to coccidiosis. In order to obtain further evidence on this point chickens of various ages kept under carefully controlled conditions were infected and studied throughout the course of the infection.