Seasonal Effects
While the stallion is effected by season, it is not near as dramatic as the effects on the mare. Season was previously shown to effect testosterone levels in stallions. It is these changing hormonal levels that are presumed to change behavior in the stallion. Low levels of testosterone occur during the winter with peak levels during the summer. Several studies have been done to demonstrate the effect of season on the stallion and are shown in the following table:
| Criteria |
Month |
Average Response |
| *Reaction Time |
January |
13.6 min |
| *Reaction Time |
July |
1.1 min |
| Number of Mounts/Ejaculate |
January |
2.0 |
| Number of Mounts/Ejaculate |
July |
1.5 |
*Reaction time is the total time the stallion was in visual contact with the mare until the beginning of copulation.
In addition to the behavior characteristics shown above, the number of sperm in an ejaculate changes with season. During the fall and winter there are 50% less sperm per ejaculate but the quality of the ejaculate (percentage of motile sperm) does not change. The quality of the ejaculate however might be poorer if the stallion has been rested a while but will improve after 2 - 3 ejaculates and sperm reserves from the epididymis are refreshed. Under natural light, stallions usually reach peak sperm production in May and June. However if placed on artificial light December 1, they will reach this peak in February and March.
Effects of