Oxidative stress occurs when the levels of reactive oxygen species (ROS) overcome the antioxidant defenses of the organism, jeopardizing several biological functions, including reproduction. In the male reproductive system, oxidative stress not only impairs sperm fertility but also compromises offspring health and survival, inducing oxidative damage to lipids, proteins and nucleic acids. Although a clear link between oxidative stress and male fertility disorders has been demonstrated in humans and laboratory rodents, little information is available about the implications of impaired redox homeostasis in the male fertility of domestic and wild animals. Therefore, this review aims to provide an update regarding the intrinsic and extrinsic factors that are associated with oxidative stress in the male reproductive system and their impact on the reproductive performance of domestic and wild animals. The most recent strategies for palliating the detrimental effects of oxidative stress on male fertility are reviewed together with their potential economic and ecological implications in the livestock industry and biodiversity conservation.

Sperm preservation is a crucial factor for the success of assisted reproductive technology (ART) in humans, livestock, and wildlife. Irrespective of the extender and the storage conditions used, semen handling and preservation negatively affect sperm quality. Moreover, oxidative stress, which often arises during semen storage, significantly reduces sperm function and compromises the sperm fertilizing ability by inducing oxidative damage to proteins, lipids, and nucleic acids. Plant extracts have recently emerged as a cheap and natural source of additives to preserve and enhance sperm function during semen storage. The present work provides an update on the use of these natural compounds as alternative additives for sperm preservation in 13 animal species, including humans. A detailed description of the effects of 45 plant species, belonging to 28 families, on sperm function during semen storage is presented. The plant material and extraction method employed, dosage, possible toxic effects, and antimicrobial properties are provided.

Spermatogenesis is a costly process that is expected to be under selection to maximise sperm quantity and quality. Testis size is often regarded as a proxy measure of sperm investment, implicitly overlooking the quantitative assessment of spermatogenesis. An enhanced understanding of testicular function, beyond testis size, may reveal further sexual traits involved in sperm quantity and quality. Here, we first estimated the inter-male variation in testicular function and sperm traits in red deer across the breeding and non-breeding seasons. Then, we analysed the relationships between the testis mass, eight parameters of spermatogenic function, and seven parameters of sperm quality. Our findings revealed that the Sertoli cell number and function parameters vary greatly between red deer males, and that spermatogenic activity co-varies with testis mass and sperm quality across the breeding and non-breeding seasons. For the first time in a seasonal breeder, we found that not only is the Sertoli cell number important in determining testis mass (r = 0.619, p = 0.007 and r = 0.248, p = 0.047 for the Sertoli cell number assessed by histology and cytology, respectively), but also sperm function (r = 0.703, p = 0.002 and r = 0.328, p = 0.012 for the Sertoli cell number assessed by histology and cytology, respectively). Testicular histology also revealed that a high Sertoli cell number per tubular cross-section is associated with high sperm production (r = 0.600, p = 0.009). Sperm production and function were also positively correlated (r = 0.384, p = 0.004), suggesting that these traits co-vary to maximise sperm fertilisation ability in red deer. In conclusion, our findings contribute to the understanding of the dynamics of spermatogenesis, and reveal new insights into the role of testicular function and the Sertoli cell number on testis size and sperm quality in red deer.

Hydrogen sulphide (H 2 S) is involved in the physiology and pathophysiology of different cell types, but little is known about its role in sperm cells. Because of its reducing properties, we hypothesise that H 2 S protects spermatozoa against the deleterious effects of oxidative stress, a condition that is common to several male fertility disorders. This study aimed i) to determine the total antioxidant capacities of Na 2 S and GYY4137, which are fast-and slow-releasing H 2 S donors, respectively, and ii) to test whether H 2 S donors are able to protect spermatozoa against oxidative stress. We found that Na 2 S and GYY4137 show different antioxidant properties, with the total antioxidant capacity of Na 2 S being mostly unstable and even undetectable at 150 µM. Moreover, both H 2 S donors preserve sperm motility and reduce acrosome loss, although the effects were both dose and donor dependent. Within the range of concentrations tested (3-300 µM), GYY4137 showed positive effects on sperm motility, whereas Na 2 S was beneficial at the lowest concentration but detrimental at the highest. Our findings show that Na 2 S and GYY4137 have different antioxidant properties and suggest that both H 2 S donors might be used as in vitro therapeutic agents against oxidative stress in sperm cells, although the optimal therapeutic range differs between the compounds. Hydrogen sulphide (H 2 S) is the most recently discovered gaseous molecule that participates in a variety of biological functions, as do nitric oxide (NO) and carbon monoxide (CO). In mammals, H 2 S can be synthesised by enzymatic or non-enzymatic pathways 1. Overall, it seems likely that most of the H 2 S produced within an organism is generated by the H 2 S-synthesising enzymes: cystathionine γ-lyase (CSE), cystathionine β-synthase (CBS), and 3-mercaptopyruvate sulphurtransferase (3-MST), with the latter coupled with cysteine aminotransferase (CAT) 2. In the male reproductive system, the expression of H 2 S-generating enzymes has been reported in the testis 3,4 , epididymis 5 , penile corpus cavernosum 6 , and spermatozoa 7,8 , which strongly suggests that this gasotransmitter is involved in sperm physiology to some extent. In a recent study, Wang et al. found that asthenospermic men show reduced levels of H 2 S in their seminal plasma and that exogenous H 2 S supplementation improves their sperm motility 8. In contrast, in boar spermatozoa, H 2 S exerts no or negative effects on sperm motility, viability, and mitochondrial membrane potential 9. With both positive and negative effects documented, there is still controversy concerning the role of H 2 S in sperm cells. This apparent discrepancy might, at least partly, be a result of H 2 S dose-and donor-dependent effects 10. According to their chemical structure and source, H 2 S donors include inorganic salts and derivatives of phosphorodithioate, garlic extracts, thioaminoacids, and anti-inflammatory drugs 11. On the basis of their release mechanism, H 2 S donors can be classified in two categories: slow-and fast-re...