Study links seminal plasma DNase to donkey sperm release from NETs

A new donkey reproduction study in Animals points to a possible role for seminal plasma DNase in helping sperm escape neutrophil extracellular traps after insemination, while also shifting sperm motility toward faster, straighter movement patterns. In the authors’ in vitro model, sperm that were first trapped by NETs and then released by DNase showed increases in CASA-measured velocity, linearity, straightness, and oscillation metrics, findings the researchers suggest may relate to physiological changes that occur before capacitation. (papers.ssrn.com)

The work fits into a larger effort to improve reproductive efficiency in donkeys, a species where assisted reproduction has lagged behind horses and other domestic animals. Prior reviews note that jennies can develop a pronounced post-breeding endometrial inflammatory response, with polymorphonuclear neutrophils entering the uterus and contributing to NET formation. Earlier donkey studies from related research groups also found that seminal plasma influences sperm-PMN binding, and that single-layer centrifugation or seminal plasma fractionation can change how sperm interact with neutrophils. (pmc.ncbi.nlm.nih.gov)

According to the study abstract and preprint record, the investigators collected donkey ejaculates, isolated PMNs from jenny blood, and created five experimental groups, including sperm with PMNs, sperm with PMNs plus DNase, and filtered sperm populations prepared with silica gel filtration. They assessed viability with eosin-nigrosin staining and motility with CASA at one, two, and three hours. Sperm viability stayed stable in PMN-containing groups, but declined in the control semen group, which the authors interpreted as a possible protective effect from PMNs under these experimental conditions. The main kinetic shift came after DNase-mediated release from NETs, with higher VCL, VSL, VAP, LIN, STR, and WOB. (papers.ssrn.com)

That mechanistic idea has precedent in equine reproduction. A 2005 Biology of Reproduction paper reported that sperm-activated neutrophils extrude DNA that traps sperm and hinders motility, and that DNase activity in seminal plasma digests that DNA and frees entangled sperm, potentially improving transport toward the oviduct. More recent donkey-specific work has suggested that a seminal plasma fraction in the 30 to 50 kDa range may contain the DNase-related activity involved in modulating sperm-PMN interaction. (academic.oup.com)

Direct outside commentary on this specific paper appears limited so far, which is not unusual for a niche reproductive biology study. Still, the broader field has framed NET biology as an important reproductive gatekeeper rather than just an antimicrobial response. Reviews of donkey reproductive disorders and NETs in reproduction both describe sperm trapping by neutrophils as part of post-insemination selection, while also highlighting the tradeoff: the same innate immune response that helps clear contaminants can reduce sperm transport if not tightly regulated. (pmc.ncbi.nlm.nih.gov)

Why it matters: For veterinarians and theriogenologists, the practical relevance is less about immediate clinical adoption and more about refining assisted-reproduction strategy in donkeys. Donkey semen preservation and AI protocols are still less standardized than in horses, and prior studies have shown that seminal plasma can be both beneficial and problematic depending on timing, concentration, and handling conditions. This new study suggests DNase activity may be one of the functional components worth preserving, mimicking, or at least accounting for when semen is processed for cooling, freezing, or in vitro embryo work. That could eventually matter for breeding programs, endangered donkey populations, and clinics trying to improve post-thaw sperm performance. (pubmed.ncbi.nlm.nih.gov)

There are also important caveats. The available details indicate an in vitro experiment, not a fertility trial, so the findings shouldn’t yet be read as evidence that DNase supplementation improves pregnancy rates. And because sperm motility changes can reflect multiple physiological states, including capacitation-associated shifts, the clinical meaning of “improved” kinetics will need confirmation in vivo and across different semen-processing workflows. That’s especially relevant in donkey reproduction, where uterine inflammation, semen storage effects, and sperm selection dynamics interact in ways that may not be fully captured in bench models. (papers.ssrn.com)

What to watch: Watch for follow-up studies testing whether DNase-linked sperm release improves AI fertility, embryo production, or post-thaw semen performance in live jennies, and whether the authors or other groups can identify a protocol-ready seminal plasma fraction or additive that preserves the beneficial effect without worsening inflammatory responses. (mdpi.com)