- Title
- Molecular mechanisms governing fertility maintenance in thoroughbred stallions
- Creator
- Griffin, Róisín
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2021
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- The equine breeding industry suffers from many inefficiencies, arising from deficits in our understanding of the mechanisms governing stallion subfertility. The delayed detection of periods of subfertility sparks a cascade of deleterious events, commencing with a rise in failed conceptions, leading to increased stallion workload as mares will have to be rebred, and culminating in a drift in the mare’s future foaling date. This in turn, significantly impacts the future sales price and racing success of offspring. Repeated breedings also lead to increased boarding and transport costs, and veterinary interventions pertaining to the mare. Improving our understanding of the molecular mechanisms underlying stallion subfertility is paramount if we are to improve the productivity and welfare outcomes of the breeding industry. Our approach to bridging this knowledge gap should focus firstly on identifying the molecular markers predictive of stallion fertility status, and secondly on identifying causal factors and the mechanisms by which they deleteriously affect sperm function and therefore, fertility. The studies encompassed within this thesis aimed to address this paucity of knowledge; first, by harnessing mass spectrometry technology to gain a greater understanding of the proteomic differences between high-quality and low-quality spermatozoa, and second, by investigating the effects of heat stress on stallion fertility as a possible causal factor of fertility losses. Herein, we present the first study to identify proteomic differences between the high- and low-quality sperm fractions of stallion ejaculates. Mass spectrometry proteomic analysis identified 1069 proteins, of which, 22 proteins were significantly more abundant in high- quality spermatozoa. The abundance of two promising candidates, a-kinase anchor protein 4 (AKAP4) and hexokinase 1 (HK1), was confirmed via immunoblotting. Furthermore, we established the functional relevance by highlighting significant correlations between protein abundance and motility parameters. The successful utilisation of high-throughput mass spectrometry technologies to identify proteomic markers of sperm quality, led us to pursue a similar methodology in identifying the key molecular pathways governing short-term fertility fluctuations in commercial stallions. We identified an inverse relationship between endogenous caseins (κ-, α-S1 and α-S2-casein) and several epididymal and seminal plasma proteins, including epididymal sperm binding protein 1 (ELSPbP1), horse seminal plasma protein 1 (HSP-1) and clusterin; with caseins being significantly more abundant during ‘high-fertility’ periods. Our subsequent in vitro experiments confirmed that caseins play an integral role in fertility maintenance, via the prevention of HSP-1 binding to spermatozoa and the preservation of lipid membrane integrity. In the final studies presented in this thesis, we focused on investigating ambient heat stress as a possible factor adversely influencing fertility and sought to elucidate the mechanisms through which fertility is affected. Our investigations revealed that current management regimens―involving stabling overnight, with paddock access during the day―expose stallions to highest ambient temperature and humidity. Through polynomial distributed lag modelling, we identified that the fertility of 40% of the studied population is likely adversely affected by ambient heat stress. Following DNA integrity assessments, we concluded that fertility losses are most likely mediated through oxidatively damaged DNA in one third of this subpopulation. Taken together, the findings reported in this thesis have enhanced our understanding of the factors affecting stallion fertility. Importantly, this collection of studies offers a molecular understanding of the pathways governing fertility maintenance and the mechanisms through which fertility is lost, and in turn, identifies novel clinical targets for the development of a multi-biomarker diagnostic platform, for the early detection and prediction of fertility decreases.
- Subject
- spermatozoa; equine; thesis in publication; infertility; capacitation; heat stress; proteomics; biomarker; fertilisation; subfertility; membrane stability
- Identifier
- http://hdl.handle.net/1959.13/1506921
- Identifier
- uon:55937
- Rights
- Copyright 2021 Róisín Griffin
- Language
- eng
- Full Text
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| Thumbnail | File | Description | Size | Format | |||
|---|---|---|---|---|---|---|---|
| View Details Download | ATTACHMENT01 | Thesis | 5 MB | Adobe Acrobat PDF | View Details Download | ||
| View Details Download | ATTACHMENT02 | Abstract | 339 KB | Adobe Acrobat PDF | View Details Download |