Improved performance in commercial broiler flocks with subclinical infectious bursal disease when fed diets containing increased concentrations of vitamin E

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Abstract
The economic effects of increased vitamin E supplementation in 79 commercial broiler flocks incorporating over 1.5 million birds was assessed. Approximately half of the flocks were fed on either a high (178 IU/kg) or normal (48 IU/kg) vitamin E-containing diet. In addition, in approximately half of the flocks subclinical infectious bursal disease (IBD) was present. Analysis of the performance data demonstrated that flocks with subclinical IBD were consistently worse (P< 0.001) for net income, feed conversion ratio and average weight per bird than flocks without the subclinical disease. The trial also indicated that the average net income of flocks with subclinical IBD and fed a high vitamin E-containing diet was 10% better (P < 0.05) than flocks with subclinical IBD and fed a normal vitamin E-containing diet. However, the trial also demonstrated that the difference between the average net income achieved by flocks without subclinical IBD and being fed on either a high or a normal vitamin E-containing diet was only 2% and not significantly different. It is suggested that the increased improved performance from high vitamin E-containing diets recorded in flocks with subclinical IBS is due to enhanced immunocompetence and increased resistance to disease. It is also suggested that under field conditions, high dietary inputs of vitamin E are most beneficial where there is a challenge to the host's defence system and significantly improved performance will occur more predictably under such conditions.