Out-of-season breeding in thyroidectomized red deer hinds
G.M. Anderson and G.K. Barrell
Animal & Veterinary Sciences Group, P O Box 84, Lincoln
University, Christchurch
Proceedings of the New Zealand Society of Animal Production. 1998,
58: 20-24
Thyroid hormones are required for the neuroendocrine processes
that cause the onset of the non-reproductive state each spring in red
deer. To evaluate the feasibility of achieving out-of-season breeding
using thyroidectomized (THX) hinds and a THX stag, oestrous behaviour
and ovulation were compared in THX (n=9) and thyroid-intact control
hinds (n=6) following synchronization of oestrous cycles with CIDRs and
joining with a THX, vasectomized stag in the breeding and non-breeding
seasons. In the control group, oestrus and ovulation were recorded in
all (100%) and none (0%) of hinds during May (breeding season) and
October (non-breeding season) respectively (P<0.05), however in THX
hinds oestrus and ovulation ocurred in a proportion of the animals
(33-55%) and this incidence was not affected by season (P>0.05). Time
of onset after synchronization and duration of oestrus were not
significantly affected by thyroidectomy or season (P>0.05). To
determine if pregnancy could be established in THX hinds in the
non-breeding season, all 15 hinds were synchronized for oestrus using
CIDRs plus 200 I.U. PMSG and joined with a fertile, THX stag in early
December. Any hinds not mated on this occasion were resynchronized using
CIDRs plus 400 I.U. PMSG and again joined with a fertile, THX stag.
While the lower dose of PMSG was generally ineffective in inducing
oestrus (i.e. only 2 THX hinds mated), 50% of control and 71% of THX
hinds which received 400 I.U. PMSG exhibited overt oestrus. In all,
seven out-of-season calvings (3 from thyroid intact and 4 from THX
hinds) were obtained from 10 matings (all 3 unsuccessful matings
occurred in THX hinds). These results imply that although thyroid gland
secretions switch off reproductive activity at the end of the breeding
season, they do have a supportive role in the expression of overt
oestrus and occurrence of ovulation.
Keywords: NZSAPAB;
red deer; reproduction; seasonal breeding; thyroid gland;
oestrus.
Last Updated 12-09-1998
