Manipulations of the Reproductive Physiology and Endocrinology of the Ewe

Audicana, Lina (1992) Manipulations of the Reproductive Physiology and Endocrinology of the Ewe. MVM(R) thesis, University of Glasgow.

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Abstract

The study is divided into three main parts, which investigate the manipulation of reproduction in the ewe with various drugs. The first part investigates the luteal function during and following progestagen synchronization of oestrus. In the second part, the efficacy of two commercially available prostaglandins (PGs) in inducing luteolysis and termination of early pregnancy is assessed. The third part studies the effect of intravaginally administered prostaglandin E2 (PGE2) on the cervix and vagina during the luteal phase. In the first part, the lifespan of the CL (assessed by daily progesterone levels and oestrous detection) was investigated during two periods of the breeding season following oestrus induction with progestagens alone (controls) or with a superovulatory dose of PMSG (PMSG+). Short cycles (<12 days) were observed at the peak of the season and in association with the use of PMSG. Results suggested that insufficiency of gonadotrophins to support the CL was not the mechanism involved in the premature CL demise. The CL function was also studied during the progestagen treatment (MPA) which was administered on different known days of the cycle. MPA, when administered at metoestrus did not suppress the maintenance of the existing CL in most ewes (6/8). This result indicates that if the CL outlasts the lifespan of the exogenous progestagen, the resulting asynchrony may be mistaken for premature regression of the supposedly induced CL. There are conflicting results about the time after maternal recognition when the CL recovers its responsiveness to PGs. Progesterone was measured (with ELISA) following PG injections at various stages of early pregnancy at doses which are luteolytic in cyclic ewes. On day 20 of pregnancy resistance was observed towards both PGs, however Estrumate produced faster luteolysis and a higher frequency of abortions than Lutalyse. Resistance to Lutalyse was demonstrated on day 28 of pregnancy, which encourages more studies in the maintenance of pregnancy after maternal recognition and embryonic attachment. In the third part, the ripening effect of intravaginal PGE2 alone or in combination with oestradiol in early pregnancy or at oestrus was evaluated. Treatment with PGE2 produced softening of the cervix but did not allow complete catheterisation. Further studies were carried out on superovulated ewes on day 6 of the cycle (PGE2 treated vs controls), using histology and SEM of the vagina and three portions of the cervix. The ultrastructural changes observed in the CT of both the connective tissue (CT) vagina and cervix of the treated animals were similar to those described in sheep and humans undergoing physiological ripening of the cervix at pregnancy and parturition. Changes were greater at the external os, suggesting that PGE2 administered intracervically may be advantageous. Squamous metaplasia was also observed in treated ewes, a change which has neither been described in the ewe nor man and warrants further investigation as metaplasia is a precancerous lesion in humans.

Item Type: Thesis (MVM(R))
Qualification Level: Masters
Keywords: Animal sciences, Endocrinology, Physiology
Date of Award: 1992
Depositing User: Enlighten Team
Unique ID: glathesis:1992-78401
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 28 Feb 2020 12:09
Last Modified: 28 Feb 2020 12:09
URI: http://theses.gla.ac.uk/id/eprint/78401

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