Equine Health Update Issue 1 Volume 16 - Page 21

This study shows that the reproductively active period of a nonpregnant mare can be advanced using lowlevel blue light to one eye fromhead-worn light masks and that this method is as effective as maintaining mares indoors under artificial lighting. While it was expected that a high proportion of mares in the barnlit and light mask wearing groups would be cycling by the end of our study, what was surprising was the large proportion of mares from these groups that were still reproductively active at the beginning of the study in mid November. As reproductive examinations are not commonly carried out at this time of year, it is often assumed that mares enter winter anoestrus earlier in the year. However, we observed a transition to anoestrus that occurred between late December and early January in the mares that were still expressing cyclicity at the start of the study in our control group. Of interest is that a lower proportion of mares from Group 3, the control group, were still expressing oestrous cyclicity at this time. It is believed that the maintenance history of each of the experimental groups contributed to their reproductive status at the beginning of the study. Due to the size of the study, it was not possible to randomly allocate mares into 3 groups from a homogeneous population. The control mares were maintained outdoors on a farm within an 8 km radius of the mares in the other experimental groups and had been living outdoors as a herd for several years prior to the study. Mares with constant exposure to the natural climatic challenges of the environment are known to exhibit a tighter breeding seas ۈ[