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Vitamin A deficiency and Eimeria acervulina infection in the chick Coles, Barbara Margaret

Abstract

The present investigation was conducted to determine the effect of an infection with Eimeria acervulina on vitamin A deficient birds. One hundred day-old chicks were divided into 2 equal groups, and one group was raised on 440 I.U. vitamin A per kilogram of feed, while the second group received the normally recommended 4400 I.U. per kilogram. At 5 weeks of age, half the birds from each group were given an immunizing infection with 3 million oocysts of E. acervulina. The clinical symptoms were more acute, and the oocyst production, mortality, and weight losses significantly higher, in the birds on the low vitamin A diet. When the birds were 9 weeks old, half were subjected to a second infection and the other half held until they were 19 weeks old. The 9-week-old birds were given an oral inoculation of 10 million oocysts to evaluate the effect of a low vitamin A diet on: the strength of the immune response; a primary infection with E. acervulina in 9-week-old birds; and the early tissue stages of the parasite in immune and non-immune birds. The results from this experiment showed that the degree of immunity is not affected by a low vitamin A ration, but primarily determined by the severity of the initial infection; and that the primary infection in 9-week-old chicks is clinically very similar to that in younger birds. The histological examinations demonstrated that the low vitamin A level used in this study did not affect the integrity of the intestinal epithelium, nor the development of the endogenous forms of the parasite. It was also shown that the sporozoite invasion was the same in immune and non-immune birds, but the schizont development was severely inhibited in the immune birds regardless of the vitamin A level. The non-immune birds on the low vitamin A ration did not show as distinct a heterophil response to infection as did the other groups. The remaining birds, half which were immunized, were maintained on their respective diets until 19 weeks of age, and during this period there was no clinical evidence of a vitamin A deficiency, and the growth rate was not significantly affected by the level of vitamin A in the diet. When 19 weeks old, the birds were inoculated with 25 million oocysts of E. acervulina to assess the effect of an extremely heavy primary infection in older birds, and to evaluate the degree of immunity still retained 14 weeks after an initial infection. The mortality was very high, and the weight losses significantly greater, in birds on the low vitamin A dietary level. Immunity, although decreased from the earlier experiment, was still present in birds on both levels of vitamin A.

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