High dietary concentrations of biotin did not prevent foot pad dermatitis in growing turkeys and external scores were poor indicators of histopathological lesions.

1. A randomised block experiment was conducted to determine the effects of increasing dietary biotin supplementation (0, 200, 800 and 1600 microg/kg) on macroscopic and histological changes associated with the development of foot pad dermatitis (FPD) in growing turkeys. 2. Each treatment was replicated in 4 pens containing 36 birds at the start of the experiment. The birds were weighed and external foot pads were scored at 2-week intervals from 2 to 14 weeks of age. A blood sample was obtained at the same ages from two birds in each pen and tissue from one foot pad was processed for histological examination. Liver samples were obtained for determination of fat content. 3. Increasing dietary biotin supplementation was associated with higher initial plasma concentrations of biotin but there was no effect on external scores or histopathology of foot pad lesions. FPD increased rapidly from 2 to 6 weeks and remained similar thereafter. There was no effect of dietary biotin on liver fat content. 4. The correlations between external foot pad scores at different ages were all less than 0.4. The correlation between external and histopathological scores was 0.56 and the respective correlations with body weight were 0.52 and 0.65. There were no differences between the body weights of birds with different external scores but high histopathological scores were associated with lower body weights. 5. It was concluded that current recommendations for biotin in wheat-soy rations for growing turkeys are adequate for normal growth and development and that higher supplements of biotin in these experimental conditions did not prevent the occurrence of FPD.