A long-day light program accelerates seasonal coat changes but is without effect on semen and metabolic parameters in Shetland pony stallions.

This research analysed whether longer daylight periods influence physical well-being or breeding parameters of Shetland pony stallions. The study found that extended lighting hastened the seasonal shedding of their coats but didn’t affect their semen qualities or metabolic rates.

Objective and Methodology

• The study was performed to understand the influence of artificial long days on various aspects of Shetland pony stallions. These aspects involve rectal temperature, heart rate, variability in heart rate, hematology, changes in coats, semen parameters and plasma testosterone concentrations.
• The researchers divided the ponies into two groups: a control group (CON) that experienced natural day-night cycles, and a treatment group (AL) that was exposed to prolonged daylight from December to late March.

Results

• Throughout the 8-month study period, rectal temperature, heart rate, and variability in heart rate showed no significant difference in both CON and AL groups. Similarly, plasma total protein, hematocrit, leukocyte, and lymphocyte counts increased first and then decreased during the study but showed no difference between the groups.
• The length of the guard hair reduced over time in both groups but the decrease happened sooner in AL stallions compared to CON stallions. The CON stallions experienced faster hair regrowth than the AL stallions.
• Overall sperm count increased from January to April in the AL group and until May in the CON group. However, the total sperm count didn’t differ between both groups. Also, sperm motility and the percentage of membrane-intact spermatozoa didn’t show any apparent seasonal variations and the parameters of semen didn’t differ between the groups.

Conclusion

• The researchers concluded that Shetland stallions showed seasonal changes in hair coats and total sperm count. However, only changes in hair coat, not semen parameters, were accelerated under a long-day light program.