Megan Campbell, D.V.M.

Thoroughbred and Standardbred breeding farms want their foals to be born as close as possible to the universal birthday of January 1st.  The eleven-month gestation period dictates that breeding should start in February for these horses.  Very few mares will be cycling at this point.  Mares that tend to have difficulty conceiving have more opportunities to be bred if they start cycling earlier in the year.  If left to their own devices, most mares will not begin to cycle normally until approximately April.  Increasing the day length artificially can trick these mares into thinking that spring has come early.  Putting your mare under lights does not skip the normal fall transitional period, it simply makes the whole process begin sooner.  The fall transitional period lasts anwhere from 40-60 days or more.  Therefore, if February breeding dates and January foals are yur goal, your mares should be put under lights for 16 hours a day starting December 1st.  A good rule of thumb is to use one 200 watt bulb for a 12 foot by 12 foot box stall.  If you have any other questions regarding getting your mares to cycle earlier in the season, feel free to contact of the Mid-Atlantic veterinarians.