This study investigated whether dietary supplementation with a multi-strain probiotic mixture (Slab51®, Sivomixx®) modulates systemic and seminal redox status and improves semen quality in healthy breeding dogs. Fourteen dogs were randomly assigned to receive either a control diet or the same diet supplemented with 400 billion CFU of lyophilized bacteria for 70 days, covering a complete spermatogenic cycle. Serum biochemical parameters and systemic antioxidant defences were evaluated at baseline and day 70. Semen was collected prior to supplementation and after 35 and 70 days of treatment. Probiotic supplementation significantly increased sperm concentration ( p 0.001) and improved key kinematic parameters, including average path velocity (VAP, p 0.05), straight-line velocity (VSL, p 0.05), curvilinear velocity (VCL, p 0.01), amplitude of lateral head displacement (ALH, p 0.05), and linearity (LIN, p 0.001), whereas beat-cross frequency (BCF), straightness (STR), and static sperm percentage remained unchanged. These improvements were accompanied by a marked reduction in seminal reactive oxygen species (ROS) and a significant increase in biological antioxidant potential (BAP) and total antioxidant capacity (TAC), indicating enhanced seminal antioxidant capacity. Systemically, probiotic-treated dogs exhibited reduced blood urea nitrogen, triglycerides, and total cholesterol, together with significantly increased superoxide dismutase, catalase, glutathione peroxidase activities, and TAC ( p 0.001). In conclusion, these findings demonstrate that multi-strain probiotic supplementation enhances systemic and seminal antioxidant defences and promotes functional improvements in semen quality in healthy dogs, highlighting the biological relevance and practical implications for breeders and clinicians. However, further studies are ongoing to deeply elucidate the effects of probiotics on semen parameters and the relationship between probiotic-induced modulation of the gut microbiota and semen characteristics, with the aim of clarifying the role of the gut–testis axis in canine fertility and reproductive health.
Losacco et al. (Fri,) studied this question.