Winter shearing enhances basal and GnRH-stimulated testosterone secretion in rams.

Rams typically show seasonal declines in reproductive activity, characterized by reduced LH pulsatility, testosterone secretion, and hormonal responsiveness during winter and early spring. The objectives of this study were to compare basal testosterone concentrations, testicular fluid content, testicular artery blood flow, and scrotal temperature in rams that were or were not sheared in winter, and to evaluate their response to a GnRH challenge. Eleven adult Corriedale rams were sheared in August (winter in the Southern Hemisphere), while another 11 rams remained non-sheared. Sheared rams showed higher basal testosterone levels (P = 0.03) and a greater testosterone response to a GnRH challenge 14 days after shearing (P = 0.04). Maximum scrotal temperatures on the days following shearing and after the GnRH challenge were similar between groups. Regarding testicular blood flow, systolic velocity (SV) and diastolic velocity (DV) varied with time, and were higher in sheared rams than in non-sheared rams. Following the GnRH challenge, SV, pixel intensity, and resistance index (RI) also varied over time and were lower in sheared rams than in non-sheared rams. Other testicular flow variables were not affected by shearing or by the GnRH challenge. This study demonstrated that winter shearing induces a sustained increase in testosterone secretion in rams, persisting for at least 2 weeks. Sheared rams also presented an enhanced testosterone secretion after a GnRH challenge applied two weeks after shearing. Testicular thermoregulation does not appear to explain these effects, as scrotal temperature remained unchanged after shearing despite exposure to cold environmental conditions.