PHOTOPERIODIC CONTROL OF ANTLER CYCLES IN DEER .3. DECREASING VERSUS INCREASING DAY LENGTHS

Deer were exposed for 3 yr to photoperiods which increased or decreased 2 h every 4 mo; starting at 4L/20D or 20L/4D, respectively. Under both sets of conditions, antlers were repeatedly shed and replaced, usually in synchrony with every other time the day lengths were changed. On decreasing days, antler cycles were omitted as the photoperiod passed the equinox (12L/12D). On increasing days, the equinoctial photoperiod induced prolonged episodes of antler growth. The tendency for the antler replacement cycle to lock onto alternate changes in artificial photoperiods was consistent with the seasonal growth of antlers every other time the day lengths changed in the natural environment. Antler replacement was apparently triggered neither by shortening nor lengthening days, but by the alteration of such changes irrespective of the direction of the shift in the photoperiod.