Acute scrotal insulation in Nelore bulls impairs oxidative phosphorylation and estrogen signaling in epididymal sperm.

The objective was to assess effects of acute epididymal heat stress (HS) on bovine sperm and seminal plasma proteomes. Fourteen Nelore bulls, ∼18 mo old, with ≥70 % motile sperm and ≥70 % morphologically normal sperm were allocated into three groups: 12H (n = 5; 12 h of scrotal insulation [SI]); 24H (n = 5; 24 h of SI); and 48H (n = 4; 48 h of SI). Semen was collected before (control samples) and immediately after SI and differentially abundant proteins (DAPs) were identified in seminal plasma and sperm. Intratesticular temperature (at the end of HS; °C) was highest in 48H (mean ± SEM; 38.6 ± 0.5a, 37.3 ± 0.3ab, 35.6 ± 0.7b, and 35.2 ± 0.2b for 48H, 24H, 12H, and Control, respectively; P < 0.05). Sperm motility and morphology were not significantly different among groups. Scrotal insulation resulted in 172 and 518 DAPs in seminal plasma and sperm, respectively. Epididymal HS caused significant proteomic changes, in both seminal plasma and sperm. In seminal plasma, downregulated proteins were primarily associated with ATP production, oxidative stress protection, immune function, and sperm cytoskeleton integrity. In sperm, proteomic alterations were strongly linked to suppression of mitochondrial electron transport (oxidative phosphorylation) and estrogen signaling, along with increased proteins involved in glycolysis/gluconeogenesis pathways. Despite these changes, sperm motility remained unaffected.