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Effect of age and time of day on the timing of the surge in luteinizing hormone, behavioural oestrus and mating in red deer hinds (Cervus elaphus)

Summary. The oestrous cycles of fourteen red deer hinds (six yearling; eight more than 2 years old) were synchronized during the early breeding season by removal of a progesterone-containing intravaginal device and blood samples were taken at intervals of 3 h commencing 13 or 25 h later and continued for 54 h. The controlled internal drug release devices (CIDRs) were removed at 08:00 h (group 1; three yearlings and four adults) or 12 h later at 20:00 h (group 2; three yearlings and four adults). There was no significant effect of time of removal of CIDR on the interval to the onset of oestrus (group 1, 34·5 ± 4·05 h; group 2, 42·14 ± 7·8 h) on the time of peak concentration (group 1, 41·81 ± 5·69 h; group 2, 41·71 ± 7·81 h) or on duration of the luteinizing hormone (LH) surge (group 1, 15·00 ± 0·95 h; group 2, 14·57 ± 0·78 h). The six yearling animals exhibited oestrus and LH surge significantly later than the adults (55 ± 4·2 versus 32 ± 6·3 h for the LH surge for yearling and adult females, respectively). In a further experiment, 20 hinds were synchronized during the breeding season by removal of CIDR at two times of day 12 h apart and placed with a stag. Mating took place at a mean time of 42·1 ± 2·4 h and 37·0 ± 1·3 h later in the two groups. There was no significant effect of time of removal of CIDR upon time to onset of oestrus. These data indicate that the timing of ovulation and onset of sexual behaviour in this species is unlikely to be controlled by a circadian gate. The significant delay in onset of oestrus in young animals suggests that either social or developmental factors may play an important role in timing ovulation in red deer following the decline of progesterone.

Keywords: red deer; oestrus; luteinizing hormone surge; circadian rhythm