Luteal stage dependence of pituitary response to gonadotrophin-releasing hormone in cyclic dairy ewes subjected to synchronisation of ovulation

dc.contributor.author	Amiridis, GS	en
dc.contributor.author	Valasi, I	en
dc.contributor.author	Menegatos, I	en
dc.contributor.author	Rekkas, C	en
dc.contributor.author	Goulas, P	en
dc.contributor.author	Papanikolaou, T	en
dc.contributor.author	Deligiannis, C	en
dc.date.accessioned	2014-06-06T06:46:43Z
dc.date.available	2014-06-06T06:46:43Z
dc.date.issued	2005	en
dc.identifier.issn	10313613	en
dc.identifier.uri	http://dx.doi.org/10.1071/RD05068	en
dc.identifier.uri	http://62.217.125.90/xmlui/handle/123456789/3155
dc.subject	Luteinising hormone	en
dc.subject	Progesterone	en
dc.subject	Sheep	en
dc.subject	Timed insemination	en
dc.subject.other	gestagen	en
dc.subject.other	gonadorelin	en
dc.subject.other	luteinizing hormone	en
dc.subject.other	progesterone	en
dc.subject.other	prostaglandin F2 alpha	en
dc.subject.other	animal experiment	en
dc.subject.other	animal tissue	en
dc.subject.other	article	en
dc.subject.other	artificial insemination	en
dc.subject.other	blood sampling	en
dc.subject.other	concentration response	en
dc.subject.other	conception	en
dc.subject.other	controlled study	en
dc.subject.other	estrus	en
dc.subject.other	female	en
dc.subject.other	hypophysis	en
dc.subject.other	luteal phase	en
dc.subject.other	nonhuman	en
dc.subject.other	ovulation	en
dc.subject.other	sheep	en
dc.subject.other	Animals	en
dc.subject.other	Breeding	en
dc.subject.other	Estrus Synchronization	en
dc.subject.other	Female	en
dc.subject.other	Gonadotropin-Releasing Hormone	en
dc.subject.other	Insemination, Artificial	en
dc.subject.other	Luteal Phase	en
dc.subject.other	Luteinizing Hormone	en
dc.subject.other	Ovulation	en
dc.subject.other	Pituitary Gland	en
dc.subject.other	Pregnancy	en
dc.subject.other	Progesterone	en
dc.subject.other	Sheep	en
dc.subject.other	Time Factors	en
dc.subject.other	Animalia	en
dc.subject.other	Ovis	en
dc.subject.other	Ovis aries	en
dc.title	Luteal stage dependence of pituitary response to gonadotrophin-releasing hormone in cyclic dairy ewes subjected to synchronisation of ovulation	en
heal.type	journalArticle	en
heal.identifier.primary	10.1071/RD05068	en
heal.publicationDate	2005	en
heal.abstract	Possible hormonal aberrations precluding conception or maintenance of pregnancy in dairy ewes subjected to ovulation synchronisation were investigated in this study. The pituitary response to exogenous gonadotrophin-releasing hormone (GnRH) was tested at different luteal stages in 36 ewes. Oestruses were synchronised by using progestagen-impregnated sponges and the animals were randomly allotted into one of three treatment groups (A, B and C; n = 12 for each). Treatments commenced on Days 4, 9 and 14 of the new cycle (oestrus was defined as Day 0). Ewes were given two GnRH injections, 5 days before and 36 h after a prostaglandin F2α (PGF2α) injection, and the animals were inseminated 12-14 h after the second GnRH injection (modified OVSYNCH). For luteinising hormone (LH) determination blood samples were withdrawn from six ewes of each group at the time of GnRH administration, and 30, 90, 180, 270 and 360 min later. Progesterone was assayed in samples taken every other day starting from oestrus and for 17 days after the second GnRH injection, and in an additional sample collected on the day of insemination. After the first GnRH injection, the LH concentration was higher in Group C than in Groups B and A (mean ± s.d.: 64.8 ± 10.0 ng mL-1, 41.3 ± 3.7 ng mL-1 and 24.6 ± 9.0 ng mL-1, respectively; P < 0.05), whereas after the second GnRH injection a uniform LH release was found in all groups. PGF2α caused a significant decrease in progesterone (P4) concentration in all groups; however, at artificial insemination ewes that conceived had significantly lower P4 concentration in comparison with those that failed to conceive. As early as Day 5, pregnant animals had higher P4 concentrations than non-pregnant animals. Overall, 21 animals conceived (seven, nine and five ewes from Groups A, B and C, respectively). These results indicate that the proposed protocol is equally effective in inducing a preovulatory LH surge at any stage of the luteal phase, and that elevated P 4 concentration along with a delayed P4 increase should be considered as a causative factor for inability to conceive. © CSIRO 2005.	en
heal.journalName	Reproduction, Fertility and Development	en
dc.identifier.issue	8	en
dc.identifier.volume	17	en
dc.identifier.doi	10.1071/RD05068	en
dc.identifier.spage	769	en
dc.identifier.epage	774	en