Body Condition, Metabolic Parameters and Semen Traits in Purebred Spanish Horses

The growing relevance of the Purebred Spanish horse has driven the extensive use of assisted reproductive technologies to preserve elite stallion genetics. Optimal reproductive performance is intrinsically linked to systemic health and high semen quality. This study aimed to evaluate the impact of body condition on the stallion's metabolic and endocrine profiles and their seminal parameters. Semen and blood samples were collected from 26 stallions (February-May in 2024-2025) whose body condition score (BCS) was assessed using the Henneke scale. They were classified into two groups, low BCS with a score range of 4-6 (n = 14) and high BCS with a score range of 7-8 (n = 12). The low BCS is regarded as a normal condition, whereas the high BCS is regarded as obesity. Metabolic and endocrine parameters and semen quality variables were analyzed using ANOVA, and principal component analyses (PCA). Stallions with high BCS showed significantly increased insulin and triglycerides concentrations (p = 0.0263 and p = 0.0046, respectively), with a positive correlation between BCS and insulin levels (r = 0.576, p = 0.04), as well as between BCS and triglyceride levels (r = 0.525, p = 0.0049). A significantly lower sperm count was observed in stallions with high BCS (p < 0.0001), together with lower total sperm motility (p = 0.0055), when compared to stallions with low BCS. PCA of blood parameters revealed the first component (PC1) associated with glucose, insulin, triglycerides, and cholesterol. In semen's PCA, PC1 was associated with quality parameters, while PC2 was influenced by total sperm count. No direct correlation was found between PCA components and BCS. However, integration of both PCA showed that increased insulin, triglycerides, and cholesterol were significantly associated with a reduced total sperm count. These findings suggest that reproductive changes in stallions with high BCS are primarily mediated by metabolic and endocrine dysfunction rather than adiposity per se.