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[