Ask the Vet: Equine Reproduction

Courtesy of AAEP

Question: I have signed a contract to breed my mare. She is 18-years-old and this is the first attempt to breed her. The stud farm wants to start the beginning of February. I am penning her every night but rely only on a big yard light, which does sufficiently light up her pen. However, due to the cost ($350/cycle) at the stud farm, I feel I should wait until the end of March when our grass starts to green up and there are naturally more daylight hours. I am not interested in an early colt. Am I on the right track or am I standing in the way of success? The light is NOT on any timer so it stays on all night. I have been told that constant light is not good. I would appreciate your view on this whole subject.

Answer: This is an excerpt from notes that I wrote for a December lecture that I gave about mare management…

Light Management Systems – Melatonin and the Pineal Gland

Light Intensity – 100w bulb in 12 x 12 foot stall should be adequate. What effect does moonlight have? Neighbor’s security floodlights?

What if you already have a lighting system? How do you know if it’s adequate? Set camera ASA setting to 400. Shutter speed should be set to 0.25 seconds. Diffuse light with a piece of paper or Styrofoam cup. If camera can take a picture at f4 then there is at least 10 footcandles or 108 lux…

When to Begin Lighting – Vernal Transition takes six to eight weeks. Start no later than December 1. Short day exposure appears to be important.

Lighting Systems – Fluorescent bulbs can work if lux is high enough.

Required Length of Photostimulation – Natural exposure requires 14.5 hours of daylight. But the longest day of the year in Florida is only 14 hours and 3 minutes.

Evening only – This is reported NOT to work prior to sunrise and MUST be altered to coincide with sunset as it changes from day to day…involves adding 2 to 2.5 hours of daylight onto the end of the day…applied at sunset Pulse Lighting (also called Night Interruption) – 9.5 to 10.5 hours after the onset of darkness, a one hour exposure to adequate candlepower. This is convenient in stalled situations but defeats the purpose of ease of management in a paddock situation…horses would have to wait in an outside paddock to anticipate the pulse of light. This would minimize the benefits of having them in a paddock in the first place.

Effect of Photoperiod on Gestation – Mares bred early in the year (during a short photoperiod) will have longer gestations. Mares exposed to long days artificially in the last third of gestation had quicker onset to foaling. We are unclear whether the exposure to photoperiod enhances the speed of the fetal maturity or if the photoperiod changes the endocrine pulses of the mare.


Question: We have a mare that has been bred (easily) through live cover two or three times and will be breeding her to a stallion that only covers via artificial insemination (AI) this year. I understand this is not always as successful with such mares. Are there any tips you could offer or opinions on the matter?

Answer: Semen that is fresh from a stallion can be expected to live five to seven days. Once you cool it and extend it for shipping, it only lives about 48 to 72 hours. If you use frozen semen, that sperm is so damaged it will consistently live six to 18 hours.

The more you process semen, the more precise you have to be with ultrasounding mares during heat, giving them drugs to induce them to ovulate when you want, and then confirming that they have ovulated to insure you don’t need to re-order semen.