Table 1.

Eligibility criteria separated into study-specific, population, and outcome components.

Question elements	Eligibility criteria
	Inclusion	Exclusion
Study-specific	English language documents (original and translated)	Publications in a language other than English or without translation
	Peer-reviewed published literature including primary and retrospective data and case reports	Data presented in review or opinion articles
	Academic grey literature including dissertations and theses, conference presentations, and posters	Duplicate data sets
Population	Domesticated Equus caballus only	Alternative sub-species of the Equus genus
Outcome	Standard methods of semen collection including an artificial vagina	Non-standard semen collection methods including epididymal retrieval
	Semen quality analysis of PMOT and sperm concentration	Semen quality parameters presented for sexed semen samples
	PMOT values analysed via CASA or microscopy	Ejaculatory stimulation via pharmacological- and electro-methods
	Sperm concentration analysis via the NucleoCounter	Stallions displaying signs of perturbed reproductive health including anatomical, seminal, and bacterial or poor libido
	Fresh and cooled semen samples	Parameters reported for cryopreserved or frozen-thawed semen