- Title
- Advances in oestrous synchronisation technology for assisted breeding in marsupials
- Creator
- Witt, Ryan Robert
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2018
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- Oestrous synchronisation technology has the capacity to advance genetic conservation outcomes for threatened marsupials by making use of selected spermatozoa in artificial insemination (AI). A technique capable of precise control of oestrus and ovulation in marsupials, of which most are spontaneous ovulators, remains the key limiting factor in developing practical AI programs. The major impediment is the corpus luteum (CL) which in marsupials becomes independent of hypothalamic-pituitary support after formation and persists in both pregnant and non-pregnant cycles. For this reason, eutherian synchronisation techniques that rely on targeting CL life have failed to induce luteolysis in marsupials. The aim of this thesis was to investigate the potential to circumvent the marsupial CL and synchronise oestrous by targeting the hypothalamic-pituitary gonadal (HPG) axis with a gonadotrophin-releasing hormone (GnRH) agonist. GnRH agonists are small molecules rapidly removed from the body and thus are traditionally delivered as multiple injections or in slow release implants not suitable for assisted breeding applications. In contrast, Lucrin® Depot (AbbVie), a GnRH agonist in microspheres effects a one-month suppression of pituitary function after a single injection. In this thesis, I detail the potential for Lucrin Depot to synchronise oestrous in two taxonomically distinct marsupials with alternative reproductive strategies, a dasyurid, the fat-tailed dunnart (Sminthopsis crassicaudata,) and a macropod, the tammar wallaby (Notamacropus eugenii). In the fat-tailed dunnart, a dose of 5 mg kg–1 or 10 mg kg–1 of Lucrin Depot, resulted in reproductive suppression for 4 to 8 weeks, a return to reproductive activity at 8 to 12 weeks, and a complete return to cycling at 16 weeks. Following Lucrin-induced suppression, female dunnarts were fertile and conceived as early as 8 weeks after receiving 5 mg kg–1 but did not conceive until 14 or 15 weeks after receiving 10 mg kg–1. In tammar wallabies that underwent removal of pouch young (Day 0 RPY), Lucrin Depot inhibited the growth of pre-ovulatory follicles (all follicles <2mm, Day 31 RPY). An effective dose, 1.25 mg kg–1, delays oestrus until between Day 39-66 RPY if Lucrin-treated at the time of RPY, and between Day 43-71 RPY if Lucrin-treated on Day 10 RPY. The outcome of work in both the fat-tailed dunnart and tammar wallaby resolved that Lucrin Depot has the capacity to inhibit ovarian follicular activity, but alone does not synchronise oestrous to a degree needed for assisted breeding. In the final research chapter, I show Lucrin Depot can be combined with exogenous gonadotrophins for ovarian stimulation and synchronisation. Pre-treatment of tammar wallabies with 1.25 mg kg-1 of Lucrin Depot on Day 0 RPY prior to single doses of 20IU of PMSG on Day 20 RPY and 500IU of hCG on Day 23 RPY, synchronised oestrus and copulation to within 1 day (Day 26±0.1 RPY, n= 5 of 6). At autopsy and follow-up ovarian histology, it was determined that 20IU of PMSG adequately stimulates the heathy growth of pre-ovulatory follicles (around 10+ follicles >3mm per ovary Day 31 RPY). However, both the control superovulation group, and the Lucrin Depot-superovulation group did not ovulate in response to a single 500IU injection of hCG. Together the data presented in this thesis confirm that Lucrin Depot can form the basis of an oestrous synchronisation strategy in marsupials, and with further work to resolve the optimum ovulation treatment, it can be expected to become a practical assisted breeding tool for the recovery of threatened marsupials.
- Subject
- marsupial; thesis by publication; conservation; assisted reproduction; oestrus synchronisation; GnRH; GnRH agonist; superovulation; wildlife
- Identifier
- http://hdl.handle.net/1959.13/1388197
- Identifier
- uon:32726
- Rights
- Copyright 2018 Ryan Robert Witt
- Language
- eng
- Full Text
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| Thumbnail | File | Description | Size | Format | |||
|---|---|---|---|---|---|---|---|
| View Details Download | ATTACHMENT01 | Thesis | 8 MB | Adobe Acrobat PDF | View Details Download | ||
| View Details Download | ATTACHMENT02 | Abstract | 559 KB | Adobe Acrobat PDF | View Details Download |