Effects of environmental temperature and season on hair coat characteristics, physiologic and reproductive parameters in Shetland pony stallions.

This research investigates the impact of environmental pressure, specifically temperature and season, on the physiology and reproduction of Shetland pony stallions. The study concludes that temperature during autumn and winter affects body temperature and hair characteristics in the ponies but its influence on semen characteristics is minimal, suggesting that reproduction function in these animals relies more on the length of day or geophysical year.

Research Methodology

• Healthy Shetland pony stallions were followed from October to June, comprising different seasons – Autumn, Winter and Spring. The ponies were divided into two groups; one group was kept in outdoor paddocks (group CON) and the other group in indoor stables (group ST).
• The research outlined the measurement of several parameters including rectal temperature, heart rate, heart rate variability, testosterone and cortisol concentrations in blood, as well as the quality and length of the coat, all of which were determined weekly.
• On a weekly basis, semen from the stallions was also collected for analysis. Additionally, the characteristics of cooled-stored and cryopreserved semen were determined once every month.

Findings of the Research

• During the stabling period, the average environmental temperature for group ST was significantly higher than group CON stallions, causing a higher average rectal temperature in the ST stallions.
• All hair coat parameters underwent seasonal changes and showed significant differences between the two groups, with the ST stallions showing shorter guard hair, slower hair regrowth and earlier hair change.
• The research found that the heart rate underwent seasonal changes; highest in Autumn, lowest in Winter and intermediate in Spring but it did not differ across the groups.
• Seasonal changes were also observed in testosterone and cortisol concentrations in blood as well as sexual behavior, but these did not differ between the two groups.
• Semen characteristics like gel-free semen volume and total sperm count reflected seasonal influence and exhibited a more pronounced increase from Winter to Spring in group CON than in ST stallions.
• However, there were no observed differences in sperm concentration in raw semen. Additionally, progressive motility of spermatozoa in raw semen was reported highest in Spring but was not influenced by the group.
• On evaluating cooled-stored and cryopreserved semen, the research found no seasonal or group effect on total motility, progressive motility or membrane integrity.

Conclusion

• The research concluded that environmental temperature during Autumn and Winter significantly influences body temperature as well as hair coat characteristics in Shetland stallions.
• The effects of temperature on characteristics of semen were minimal, indicating that the reproductive function of horses depends more heavily on day length or the geophysical year than other environmental factors.