Analysis of the Osmolarity of the Liquid Fraction of Squirrel Monkey's Semen (Saimiri collinsi Osgood, 1916) in Fattening and Non-Fattening Conditions

BACKGROUND: The aim was to determine seminal osmolarity in S. collinsi and evaluate whether it, along with seminal parameters, varies between fattening and non-fattening conditions and across age groups. METHODS: Biometric and seminal parameters were evaluated in nine S. collinsi males across conditions. Mixed-effects models assessed reproductive parameters and seminal quality. RESULTS: Seminal osmolarity ranged from 300 to 500 mOsm/L and varied with age and fattening condition. Testicular volume was lower during non-fattening. Seminal osmolarity showed linear and quadratic associations with reproductive biometry and sperm quality. Seminal volume decreased with increasing osmolarity, whereas sperm morphology and vigor showed non-linear associations. Age was negatively associated with plasma membrane integrity and sperm morphology, while sperm concentration and motility were not significantly affected. CONCLUSION: Seminal osmolarity and age are associated with reproductive and sperm functional parameters, establishing the first baseline for seminal osmolarity in this species and supporting reproductive biotechnology and conservation strategies.