Changes in pituitary responsiveness to exogenous hypothalamic hormones were assessed during seasonal anoestrous in dry, pregnant and lactating hinds. Of the fifteen adult red deer hinds monitored, five were non-pregnant, five had their calves removed immediately after birth, and five suckled their calves. All hinds were given a single i.v. injection of hypothalamic releasing hormones (5mg each of GnRH, GRF and TRH) on four occasions between Nov/Dec (10 days prior to calving) and March. The pituitary response was determined from changes in plasma concentrations of LH, growth hormone, and prolactin in samples obtained by jugular venepuncture at 0, 15 and 30 min after injection. Reproductive state significantly (P<0.001) affected LH release with a mean response (over all sample dates) of 1.12 ng/ml in dry hinds compared with 0.85 ng/ml in hinds that had their calves removed and 0.60 ng/ml in lactating hinds. Neither growth hormone (average 5.65 ng/ml) nor prolactin (average 33.9 ng/ml) responses were affected by reproductive status.
Proceedings of the New Zealand Society of Animal Production, Volume 61, Christchurch, 141-143, 2001
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