INFLUENCE OF GLUCOSINOLATES AND FREE OXAZOLIDINETHIONE IN A LAYING DIET CONTAINING A CONSTANT AMOUNT OF SINAPINE ON THE THYROID SIZE AND HEPATIC TRIMETHYLAMINE OXIDASE ACTIVITY OF BROWN-EGG LAYERS

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Abstract
The effects of varying amounts of glucosinolate and free oxazolidinethione (OZT) in laying diets containing a constant amount of sinapine on thyroid size, hepatic trimethylamine (TMA) oxidase activity, and TMA levels in plasma and egg contents were studied. The diets fed contained aqueous extracts of RSM produced from high, medium and low glucosinolate cultivars (Oro, Span and Tower) which were included in amounts that provided the same level of sinapine in each diet. Thyroid size, plasma TMA levels and liver TMA oxidase activity were determined and eggs from individual birds in each treatment were analyzed for TMA content. The presence of progoitrin and free OZT in a laying diet significantly increased (P < 0.05) thyroid size and severely depressed hepatic TMA oxidase activity of the birds as compared to those fed a control diet. The degree of thyroid enlargement was largest for birds fed the Oro extract and was least for birds fed the Tower extract. The decrease in hepatic TMA oxidase activity, however, was greatest for layers fed the Tower extract and least for those fed the Oro extract. The decrease in TMA oxidase activity led to elevated plasma TMA levels and increased TMA content of eggs of brown-egg layers. Key words: Rapeseed meal, glucosinolate, oxazolidinethione, thyroid size, TMA oxidase, brown-egg layers