Thermoregulation of the testicle in response to exercise and subsequent effects on semen characteristics of stallions

Abstract

Stallions (n = 8) were implanted with a thermal sensory device in the muscle of the neck and the subcutaneous tissue of the scrotum and then assigned to either a nonexercise (Non-EX; n = 4) or exercise (EX; n = 4) group. A motorized equine exerciser was used to work EX stallions 30 min/d for 4 d/wk during a 12-wk period from July through October 2010. Temperatures (subcutaneous scrotal, intramuscular neck, and rectal) were recorded at 0, 22, and 30 min after the start of exercise, as well as 60 and 120 min post-exercise. Hourly ambient temperature and relative humidity data were also obtained. Semen was collected at 0, 4, 8, and 12 wk and analyzed for volume, sperm concentration, total sperm numbers, percentages of total and progressively motile sperm, sperm morphologic characteristics, and sperm DNA quality. No effect (P > 0.05) of exercise was observed on any of the measured semen variables. Implantation of thermal sensory devices had no demonstrable acute or chronic effects on the scrotal or neck tissue, indicating that the thermal sensory devices are a safe and effective way to measure subcutaneous scrotal and neck temperatures. At 22 and 30 min of exercise, rectal and neck temperatures increased (P < 0.0001) approximately 1.9 and 2.4°C, respectively, and scrotal temperatures simultaneously increased, although not significantly (P = 0.33), approximately 0.8°C. Correlations existed between scrotal, neck, rectal, and ambient temperatures, with the correlation between scrotal and rectal temperatures being greatest (r(s) = 0.76; P < 0.0001). Although moderate exercise for a short duration in extreme heat and humidity did significantly increase core body temperatures in stallions, scrotal temperatures did not significantly increase, and sperm parameters were unaffected.

The relationships between scrotal surface temperature, age and sperm quality in stallions

“…Hypoxia can lead to cell death, thus initiating testicular degeneration . After evaluating the effect of thermal stress on bovine semen, Fernandes et al (2008) observed a reduction in semen quality after scrotal insulation, whereas Mawyer et al (2012) did not observe this result in miniature horses.…”

A Preliminary Comparison of Semen Quality between Competing and Non-Competing Equine Stallions

“…Thermal stress has more recently been associated with decreased semen parameters, including progressive motility [32,33]. In equine research, thermal stress is a debated topic area with no conclusive results [34], suggesting further research into the effect of testicular thermal stress with regards to semen quality and exercise could be completed.…”

Sperm DNA quality evaluated by comet assay and sperm chromatin structure assay in stallions after unilateral orchiectomy

“…Some studies have failed to report an adverse effect of extreme exercise or elevated environmental temperature on sperm quality [11,12]. Scrotal insulation for 24 to 48 hours, however, results in a significant reduction in sperm quality [5,10].…”

“…The effect of heat stress on stallion sperm quality has been studied previously using models that insulate the scrotum, revealing an associated decline in sperm motility, morphology, and DNA quality, as well as total sperm numbers [5,6,10]. In contrast, physical exercise during hot weather was modeled to study the effects of moderate-to-strenuous exercise on sperm quality [11,12]. In both studies, despite an increase in both body and scrotal temperatures, sperm quality (i.e., sperm motility, morphology, DNA quality, and total sperm number) was not affected.…”