Gut-testis axis in roosters: Lactiplantibacillus plantarum supplementation improves reproductive performance

Probiotics are widely used in poultry farming and industry, as they offer numerous health and performance benefits for birds. Probiotic Lactobacilli maintain gut microbiota balance, aid nutrient utilization, boost the immune system, increase stress resistance and serve as antibiotic alternatives. However, their impact on male reproductive function is not yet fully understood. This study investigated the effect of a novel probiotic strain, Lactiplantibacillus plantarum SNI3 (LbSNI3), on the reproductive performance of roosters. Twenty adult roosters were used. LbSNI3 was administered orally (dose: 2 × 10⁷ CFU/animal/day) for 7 weeks to half of the animals. Control birds (10) received sterile tap water vehicle. Ejaculate volume, sperm concentration, sperm motility, number of IPVL penetration holes and testosterone plasma concentration have been measured weekly. Testis weight, dimensions and histology have been determined at the end of the experiment. mRNA levels of select genes, involved in spermatogenesis and sperm motility, oxidative and steroid synthesis have been measured in the testis samples by qRT-PCR. Total antioxidant capacity, superoxide dismutase (SOD) enzyme activity and malondialdehyde (MDA) levels were also analyzed. LbSNI3 administration increased the ejaculate volume, sperm concentration and the number of penetration holes, resulting in a significant improvement in the reproductivity index. In contrast, testosterone levels were not statistically different in control versus LbSNI3-treated groups. At the end of the experiment, testis size, the area, and the lumen of seminiferous tubuli were increased in LbSNI3-treated roosters. The testicular expression of Gpx1, Sepw1, Dio2, Birc5 and Rec8 genes was elevated following oral administration of LbSNI3. Total antioxidant activity, SOD activity significantly increased, while MDA concentration decreased, indicating enhanced antioxidant capacity in the testis. LbSNI3 produces a bacterial metabolite, γ-glutamyl-glutamate, which enters the glutathione cycle and strengthens the testicular defense mechanisms against oxidative stress. In conclusion, oral administration of probiotic LbSNI3 enhances antioxidant defense mechanisms in the testis, leading to increased reproductive index in adult roosters. This effect may be mediated through the gut-testis axis and could be utilized to improve productivity in the livestock industry.