SEASONAL PATTERNS OF GROWTH, VOLUNTARY FOOD-INTAKE AND PLASMA-CONCENTRATIONS OF PROLACTIN, INSULIN-LIKE GROWTH-FACTOR-I, LH AND GONADAL-STEROIDS IN MALE AND FEMALE PRE-PUBERTAL RED DEER (CERVUS-ELAPHUS) REAREDIN EITHER NATURAL PHOTOPERIOD OR CONSTANT DAYLENGTH

Red deer calves were reared from birth to 16 months in either constant intermediate 12L: 12D daylength (ID) or in natural photoperiod (NP) ( four males and four females per group) to investigate effects on the s omatotropic and reproductive axes, and to compare responses between th e sexes. Measurements, starting from 3 months (September), were made e ach week of live weight (LW), voluntary food intake (VFI), plasma prol actin, plasma insulin-like growth factor-1 (IGF-1), and plasma progest erone (females), and every 2 months of pulsatile LH secretion, plasma testosterone (males), responses to exogenous GnRH, and antler developm ent (males). Both sexes in ID compared with NP had significantly highe r LW gain (males, P < 0.001; females, P < 0.01) and VFI (P < 0.001) be tween winter solstice (WS) and spring equinox (SE), and VFI between SE and summer solstice (SS) (males, P < 0.05; females P < 0.01). Both se xes had significantly lower plasma prolactin concentrations in ID than in NP (males, P < 0.05; females, P < 0.01) between SE and SS. However ; plasma IGF-1 teas only significantly altered in males, being signifi cantly higher In ID than NP between WS and SE (P < 0.01). ID and NP fe males showed no significant differences in pulsatile LH secretion nor in the timing of pubertal ovulation. However, ID compared with NP male s at 10 months (just after SE) had higher LH and testosterone pulse fr equencies (P < 0.01), and at 12 months (just before SS) had higher mea n testosterone concentrations (P < 0.01) and testosterone response to GnRH challenge (P < 0.001). ID antlers hardened earlier at 11 months t han NP antlers at 14 months (P < 0.01). Thus ID compared with NP in bo th sexes prevented the winter reduction in growth and appetite and the summer elevation in prolactin secretion, and in males, but not in fem ales, stimulated higher IGF-1 secretion in winter, an earlier increase in LH pulse frequency, and an earlier increase in gonadal steroid pro duction. This study has therefore revealed some intriguing similaritie s and contrasts in the responses to photoperiod shown by young male an d female deer.