Lacticaseibacillus rhamnosus OF44 Attenuates Bone Loss in Ovariectomized Rats

Estrogen deficiency compromises bone structure and mechanical competence, creating a need for interventions that preserve both. The bone-health effects of the probiotic candidate Lacticaseibacillus rhamnosus OF44 have not been established. We evaluated OF44 in ovariectomized (OVX) rats, using micro-CT and biomechanical testing to assess skeletal outcomes and serum assays, histology, protein profiling, and 16S rRNA gene sequencing to characterize accompanying biological changes. Thirty female Sprague–Dawley rats were assigned to Sham, OVX, and OF44 groups (n = 10 per group; n = 6 per group for endpoint analyses). OF44 was administered by oral gavage at 5 × 108 CFU/kg body weight/day for 90 days. Relative to OVX controls, OF44-treated rats had higher femoral bone mineral density (0.179 versus 0.132 g/cm3; +35.5%), trabecular bone volume fraction (10.10% versus 7.01%; +44.1%), and maximum load (+17.7%). These improvements were accompanied by a favorable serum bone turnover profile, fewer TRAP-positive osteoclasts, and increased serum IL-10. OF44 treatment also altered bone-remodeling-related protein expression and gut microbial composition, including enrichment of Ruminococcaceae and S24-7/Muribaculaceae. The convergent structural and mechanical outcomes provide strain-specific preclinical evidence for OF44 as a probiotic candidate for bone health under estrogen-deficient conditions.