Male reproductive trends in the novel equine model: Investigations into anthropogenic environmental chemical exposure

Harris, Imogen

Abstract

Introduction: Adverse trends are reported in human, canine, and bovine reproductive health, associated with exposure to environmental chemicals (ECs). Poor testicular function in stallions poses an economic, health and welfare concern. Assessing equine testicular EC accumulation initiates this species as a sentinel for human reproduction and a biomonitor for terrestrial environmental health. Trends in semen quality in global and UK-based equines and the potential aetiological involvement of EC exposure are investigated within this thesis.
Methods: A comprehensive evidence synthesis and meta-regression analysis determined trends (1984-2019) in objectively analysed fresh sperm progressive motility (PMOT; %; n=230 articles) from global equine populations. Trends were analysed in sperm motility (TMOT; %), concentration (million/ml), volume (ml), and total sperm output (TSO; million) in a UK-based equine population from a single breeding facility (2001-2020; 11,387 samples; 1,036 stallions). A linear mixed model (REML) accounted for predetermined variables. For EC analysis; testes (n=6), soils (n=2), grass (n=2), and feedstuffs (n=6) were analysed for Σ7PCBs, Σ7PBDEs, Σ16PAHs, and DEHP (GC-MS). EC concentration statistics incorporated an ANOVA and Tukey’s post hoc, or an independent t-test.
Results: PMOT declined by 31.89% between 1984 and 2019, irrespective of sensitivity analyses (p<0.05). In the UK-based equine population, TMOT declined by 10.10% (2001 and 2010), whilst concentration, TSO, and volume increased. All chemicals analysed were detected in testicular samples, feedstuffs, and pastures.
Conclusions: Adverse trends in two sperm motion characteristics raises concern regarding the reproductive health and fertility of the equine population. This research provides novel data on equine testicular EC accumulation and suggests ingestion as a key exposure route. The research initiates the use of the novel equine model as a sentinel species for reproductive trends and as a biomonitor species for terrestrial ecosystems. Further research is required to determine whether EC exposure is associated with declining equine motility trends.

Citation

Harris, I. Male reproductive trends in the novel equine model: Investigations into anthropogenic environmental chemical exposure. (Thesis). University of the West of England. Retrieved from https://uwe-repository.worktribe.com/output/10017876

• Thesis Type: Thesis
• Deposit Date: Oct 3, 2022
• Publicly Available Date: Aug 10, 2023
• Public URL: https://uwe-repository.worktribe.com/output/10017876
• Award Date: Aug 10, 2023