Paget, Walpole & Richardson (1961) reported that the oral administration of the hydrazine derivative methallibure (1-α-methyl-allyl-6 methyldithiobiurea, ICI 33828, Aimax) to rats resulted in a selective and reversible inhibition of pituitary gonadotrophic function. Subsequent work (Gerrits & Johnson, 1964; Polge, 1964) has demonstrated that this compound can be included in the ration and is highly effective for synchronization of oestrus in swine. Satisfactory results have been obtained in many controlled breeding trials and results indicate that methallibure would be of practical use in commercial breeding programmes. Some side effects, such as appetite suppression (Stratman & First, 1965) and inhibition of milk secretion in sows (Gerrits, Johnson & Kraeling, 1965), have been reported but these are not persistent or serious.One problem with any medicated feed is that quantities in excess of that actually required for feeding
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