Not Such a Stud on the Treadmill?

Treadmill training can be detrimental to your stallion's fertility, say Swiss researchers who recently published a paper on the topic. Not only can repeated strenuous treadmill sessions adversely affect sperm quality and freezability, but the effects can last up to a month after training is concluded.

"The objective of this study was to investigate changes of quality and freezability of stallion semen in response to repeated acute treadmill exercise," wrote the researchers, who completed the study at the University of Zurich's Clinic of Reproduction. This study appeared in the June issue of Theriogenology.

The scientists collected, evaluated, and froze ejaculates from 11 stallions on a weekly basis during four four-week periods. Each week was defined as before (Period 1), during (Period 2), or after (Periods 3 and 4) intense exercise. They evaluated the gel-free volume, sperm concentration, motility, normal sperm, and sperm with major defects in fresh semen. Sperm motility and viability were examined in frozen-thawed semen.

The stallions were exercised during Period 2 twice a week on an indoor high-speed treadmill (eight sessions total on the treadmill for each horse) using an incremental workload test. "Please note that the stallions were not in good training condition and that treadmill does not represent a 'regular' work in the horse," said Dr. Fredi Janett, lead author on the study.

Heart rates and blood concentration of cortisol, testosterone, and lactates were measured.

"Results of our investigation demonstrate that heart rate and the plasma concentrations of cortisol (a sign of stress), testosterone, and lactate significantly increased during each exercise session," wrote the researchers. "Furthermore, significantly more major sperm defects were present in Periods 3 and 4 than in Periods 1 and 2."

They also noted acrosome (a membrane-bound compartment at the tip of the head of the sperm) defects increased toward the end of the exercise period, but had returned to pre-exercise value within three weeks.

"The adverse effect of physical stress might be the result of elevated glucocorticoid (any group of corticosteroids involved in metabolism) levels or increased body temperature compromising testicular thermoregulation during strenuous exercise," wrote the researchers. "Direct or indirect action of glucocorticoids on spermatogenesis has been observed in bulls, and damage to spermatogenic cells is also known to occur by increased testicular temperature in the stallion and other species."

A previous study showed regular exercise on the longe line at a walk and trot didn't influence semen quality. Another study showed that sperm motility improved in Warmblood stallions that were competing on a regular basis as compared to stallions that were only used for breeding. The researchers on the current study say it's difficult to compare the results from those other studies to the current one because in the other studies, exercise intensities were either minimal or not standardized, semen quality and sperm morphology were not evaluated in every case, and none them tested freezability.

"In frozen-thawed semen, motility was significantly lower in Period 2 compared to Period 4 and viability was significantly lower in Period 2 than in Periods 1 and 4," they continued. "Our results clearly demonstrate that in the stallion, repeated strenuous treadmill exercise can negatively influence semen quality and freezability.

"Furthermore," they concluded, "repeated physical stress during four weeks can compromise the quality of fresh and frozen-thawed semen during and up to one month."

About the Author

Stephanie L. Church, Editor-in-Chief

Stephanie L. Church, Editor-in-Chief, received a B.A. in Journalism and Equestrian Studies from Averett College in Danville, Virginia. A Pony Club and 4-H graduate, her background is in eventing, and she is schooling her recently retired Thoroughbred racehorse, Happy, toward a career in that discipline. She also enjoys traveling, photography, cycling, and cooking in her free time.

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