Pharmacological manipulation of the mammalian circadian clock: implications for the control of seasonal reproductive cycles.

Although artificial control of the light cycle can be used to regulate the seasonal reproductive cycle of many animals under laboratory conditions, such regulation is often not possible in a standard agricultural environment. An alternative strategy for regulating the seasonal reproductive cycle of photoperiodic animals is to use drugs that either mimic the effects of light on reproductive function or that induce an alteration in the way the circadian clock system is entrained by the light cycle. The ability to use drugs to achieve these objectives has been demonstrated in the laboratory, but it remains to be determined if such an approach can be used to regulate the breeding season of farm animals under normal agricultural conditions.