Effects of an oestrogen analogue on plasma LH concentrations in red deer (Cervus elaphus) hinds : A dissertation submitted in partial fulfilment of the requirements for the Degree of Bachelor of Science (Honours)
1996
Janes, Wendy L.
LH secretion is actively suppressed during anoestrus. Overcoming active inhibition toward the end of anoestrus would increase the secretion of LH and possibly advance the onset of the breeding season in a highly seasonal animal like the red deer hind. In the present study, the effect of tamoxifen, an oestrogen analogue, on LH secretion was examined in both intact and ovariectomized red deer hinds. Lactating (n=8) and non-lactating hinds (n=7) received daily injections of tamoxifen for 10 days. A further group of lactating hinds (n=8) received a vehicle injection. Plasma LH concentration was not affected by treatment with tamoxifen. Following progesterone/PMSG treatment, hinds from all groups showed oestrous behaviour and mating. Non-lactating hinds exhibited a significant decrease in the onset of oestrus (p<0.05) and increase in the duration of oestrus (p<0.05). In a second experiment ovariectomized hinds were treated with tamoxifen (n=5) or a vehicle (n=4) and given a subsequent injection of oestradiol. The suppressive effects of oestradiol on LH secretion were not affected by tamoxifen treatment. Collectively these two experiments indicate that tamoxifen does not act as an anti-oestrogen on LH secretion in red deer, and would be not be suitable for the manipulation of the breeding season. In a third experiment LH secretory patterns were measured before and after the injection of tamoxifen (n=5) or a vehicle (n=4) in ovariectomized hinds. The number of LH pulses after injection of tamoxifen was significantly reduced (p<0.05). Results of this final study show that tamoxifen acts as an oestrogen agonist on LH secretion in red deer hinds which explains why it would be unsuitable for manipulation of the breeding season in red deer hinds.
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