1. Three experiments were conducted to investigate the relationships between blood pyruvate carboxylase (pyruvate: carbon dioxide ligase (ADP-forming), EC 126.96.36.199; PC) activity, growth performance and dietary biotin level in broilers under different husbandry conditions. Blood PC activity was also used to gain information on the ingestion of biotin of faecal origin by birds housed on wood shavings and the effect of steam-pelleting on the biotin content of diets.
2. Blood PC activity and relationship to dietary biotin level were similar in birds kept under different husbandry conditions.
3. Biotin requirement for growth was higher in birds kept under conditions that allowed them to reach their growth potential more fully.
4. The contribution of biotin of faecal origin to the biotin intake of birds housed on wood shavings was negligible at 3 weeks of age but by 7 weeks was equivalent to approximately 0.01 mg/kg diet.
5. Steam-pelleting did not affect the stability or availability of biotin of natural or synthetic origin in diets.
6. It is concluded that blood PC activity is a good criterion of biotin status and requirement in fast-growing
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