Abstract
Increasing day length in spring stimulates reproductive functions in horses. In this study, we have analysed the effect of artificial long days on the quality of cooled-stored and cryopreserved semen in Shetland stallions. Stallions of the treatment group (AL, n=8) were exposed to 16h light and 8h darkness from 15th December to 20th March while control stallions (CON, n=7) were kept under natural photoperiod. Semen was collected once weekly and processed for cooled-storage and cryopreservation once per month. Total and progressive motility and percentage of membrane intact spermatozoa were analysed at 24, 48 and 72h of cooled-storage and after freezing-thawing, respectively. Total and progressive motility and membrane integrity decreased during cooled-storage for 72h in each month and both groups (p<0.001). All these parameters were lower in CON versus AL stallions (p<0.05) and the decrease was more pronounced in group CON (storage time x group p<0.05). Differences between groups decreased throughout the observation period from January (p<0.05 between groups) to July (e.g. total motility after 72h of cooled-storage in January for group AL 80±3 and group CON 49±12%, respective values in July, 83±2 and 72±6%). Neither total and progressive motility nor percentage of membrane-intact and morphologically defect spermatozoa in frozen–thawed semen differed between groups and months. In conclusion, motility of cooled-stored semen was reduced in January and increased in stallions kept under a long day light programme for at least 30 days.
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