Respostas termofisiológicas e reprodutivas de carneiros deslanados submetidos a estresse térmico moderado induzido por insulação escrotal

Abstract

This study investigated the effects of heat stress on thermoregulatory and reproductive responses in hair sheep, using scrotal insulation as an experimental model. Seven adult rams were subjected to scrotal insulation for seven consecutive days in a longitudinal design consisting of pre-insulation (4 weeks), insulation (1 week), and post-insulation (9 weeks). Four semen collections were performed during the pre-insulation phase and nine during the post-insulation phase, with continuous environmental monitoring. During insulation, thermophysiological parameters were recorded after 24 h (D2) and 96 h (D4). Semen was evaluated for sperm kinetics by CASA, concentration, morphology, DNA integrity, and binding pattern of Ram Seminal Vesicle Proteins (RSVPs) by immunocytochemistry. Reproductive variables were analyzed using the Friedman test, while individual thermotolerance was determined by principal component analysis (PCA), with group comparisons performed using the Kruskal–Wallis test. The maximum recorded temperature was 35.1 °C and the minimum was 25.8 °C. Relative humidity ranged from 84.1% to 45.0%. Scrotal insulation increased scrotal surface temperature by 0.75 °C and epididymal tail temperature by 0.90 °C compared with pre-insulation values (33.25 °C and 31.75 °C), without changes in rectal or ocular temperature. Thermal gradients decreased during insulation, from 3.00 °C to 1.96 °C (ocular–scrotal) and from 7.35 °C to 6.01 °C (rectal–epididymal), with recovery after insulation removal. Total motility decreased (p < 0.05) from 85.2 ± 2.2% to 40.6 ± 13.6% in the second post-insulation week, reaching 23.4 ± 10.4% in the fourth week, with recovery by the sixth week (67.7 ± 6.2%; p > 0.05). Progressive motility declined from 80.4 ± 2.5% to 38.3 ± 13.2% and 19.2 ± 8.9%, returning to 59.1 ± 6.9% in the sixth week. Scrotal circumference varied from 30.3 ± 0.7 cm (pre-insulation) to 31.4 ± 0.6 cm (p > 0.05) and decreased to 28.6 ± 0.5 cm in the third week (p < 0.05). Normal morphology dropped from 89.9 ± 4.2% to 39.7 ± 13.2% in the third week, recovering to 75.8 ± 5.6% in the seventh week (p > 0.05), while major defects increased from 4.9 ± 2.3% to 53.9 ± 9.9% in the fifth week. DNA integrity decreased from 92.9 ± 1.5% to 78.1 ± 1.7%, reaching 24.1 ± 9.8% in the fourth week, with recovery to 88.1 ± 1.4% in the seventh week. RSVP binding intensity declined from 3.8 ± 0.7 × 10⁶ AU to 0.7 ± 0.2 × 10⁶ AU, normalizing by the seventh week. PCA distinguished low- and high-thermotolerance groups, with HTT animals showing higher (p < 0.05) total motility (73.6 ± 2.7% vs. 62.2 ± 4.7%), progressive motility (68.2 ± 2.9% vs. 58.7 ± 4.5%), concentration (3.2 ± 0.07 × 10⁹ vs. 2.8 ± 0.1 × 10⁹ sperm/mL), and DNA integrity (81.2 ± 2.6% vs. 70.2 ± 4.4%). In conclusion, seven days of scrotal insulation impair thermoregulation and induce reproductive losses, with heterogeneous responses among animals, highlighting interindividual variability under heat stress.