Cycles of antler and testicular growth in an aseasonal tropical deer (Axis axis).

Antler and testicular cycles were studied in a group of free ranging axis deer stags kept out of doors in southern England. Within the herd, there was little evidence of a clear seasonal synchrony in the antler cycle. Detailed information obtained from 4 stags indicated that there was a fixed relationship between stage of the antler cycle and testis diameter; minimum testis diameter occurred 1-2 months after antler casting whereas maximum testis diameter occurred when stags were in hard antler. Changes in body weight, circumference of the neck and plasma testosterone concentrations largely paralleled those of testis diameter. Motile spermatozoa were collected at all stages of the testis cycle. Six animals in the early stages of antler growth were selected from the herd in May and 3 of these were implanted with 1 g melatonin in a Silastic rubber envelope. Each animal was captured on 3 subsequent occasions at monthly intervals. Melatonin was without effect on the rate of increase in size of the testis, circumference of the neck or growth and cleaning of the antlers although 1 of the treated animals failed to cast his antlers at the expected time 8 months after cleaning. We conclude from this study that there is little or no seasonal photoperiodic entrainment of the antler and testicular cycles of males in this population of axis deer.