The proposed use of melatonin in controlled sheep breeding.

The regulation by melatonin of hypothalamic-pituitary events in the ewe to advance seasonal oestrous activity, with no undesirable effects upon fertility, and its induction of those seasonal responses associated with short days indicates an essential role for melatonin in controlled-breeding programs in major sheep-producing countries. The development of suitable controlled-release systems to provide a choice of practical methods of melatonin delivery under field conditions is discussed as also are geographical and breed factors in controlled breeding with melatonin.