The influence of birth date on the development of seasonal cycles in red deer hinds (Cervus elaphus)

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Abstract
The relative importance of age and photoperiod in the timing of seasonal 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 born 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 seasonal voluntary food intake (VFI) cycle, or in the timing of seasonal changes in rate of live‐weight gain, although mean live‐weight gain was significantly greater for group L than group E during the first winter of life.Four animals in group L retained their calf coats throughout the first winter. In group L, the first summer coat fibres appeared approximately four weeks earlier, and mean fibre length for the subsequent 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 mean 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 corrected for differences in VFI were similar throughout the year.It is concluded 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 towards the end of the calving season.