THE INFLUENCE OF BIRTH DATE ON THE DEVELOPMENT OF SEASONAL CYCLES IN RED DEER HINDS (CERVUS-ELAPHUS)

The relative importance of age and photoperiod in the timing of season al cycles was studied in red deer during the first 18 months of life. Seasonal cycles of appetite, live-weight change, coat growth, oestrus and metabolic rate were examined in two groups of seven hind calves bo rn in early May (group E) or nine weeks later in July (group L). There was no difference between groups in the timing or amplitude of the se asonal voluntary food intake (VFI) cycle, or in the timing of seasonal changes in rate of live-weight gain, although mean live-weight gain w as significantly greater for group L than group E during the first win ter of life. Four animals in group L retained their calf coats through out the first winter. In group L, the first summer coat fibres appeare d approximately four weeks earlier, and mean fibre length for the subs equent winter coat was longer in group L than in group E. There was no difference between groups in the timing or amplitude of the seasonal cycle of plasma prolactin concentration, or in the incidence and mean time of onset of puberty. There was no difference between groups in me an energy expenditure per unit of live weight at any time of the year. Mean daily energy expenditure was significantly higher in summer than in winter, but values measured when the animals were resting and corr ected for differences in VFI were similar throughout the year. It is c oncluded that the seasonal cycles of appetite, live-weight change and oestrus in young red deer hinds are not modified by age, although the normal cycle of coat replacement can be disturbed in animals born towa rds the end of the calving season.