Last Updated on June 1, 2022
Interested in breeding from your mare? Let’s find out all about breeding horses, including the light effects on estrous cycle in horses!
What Is The Estrous Cycle In Horses?
Horses, like many other mammals, have an estrous cycle. This is a series of hormonal and physical changes that occur within the body over a set period of time, in order to allow the horse to breed. The average length of an estrous cycle in the horse is 22 days.
The estrous cycle of horses is divided into two stages:
The diestrus part of the estrous cycle of the mare lasts for 15-19 days. During this part of the cycle the mare will not be receptive to the stallion, as she is not fertile.
Estrus – Light Effects On Estrous Cycle In Horses
This part of the cycle is when the mare is fertile. Changes occur within the reproductive tract, and the mare will ovulate. Ovulation means that she has produced an egg, ready for fertilization if mating occurs.
Estrus lasts for 3-7 days, and is often referred to as the mare being ‘in heat’ or ‘in season’. If the mare is not pregnant at the end of estrus, she returns to diestrus and the cycle starts again.
Read more about What Is High Hind End Lameness In Horses?
Light Effects On Estrous Cycle In Horses Explained
Horses are seasonal breeders – they do not breed all year round, but instead have a mating season that lasts for several months. This is similar to many large herbivores, who time their pregnancy and birthing period to take advantage of the optimum weather conditions.
The gestation period of a horse is around 11 months, and in the wild, a mare will normally give birth during the spring. This means she must have mated by late spring, to give birth just under a year later. Being born in the spring gives the foal the best chance of survival, as the weather is warmer and food for the mare is more abundant.
Seasonally Polyestrous Or Anestrous – Light Effects On Estrous Cycle In Horses
The annual breeding cycle of a horse is referred to as ‘seasonally polyestrous’, meaning that she only cycles during the reproductive season. During the rest of the time, the mare goes through a period called anestrous, where no reproductive cycles happen at all.
Depending on the location, most mares finish anestrous in early spring and start to come into season. These may follow an irregular pattern at first, but will soon settle into a regular cycle. But how does a mare know when the time is right to start becoming reproductively receptive? Well, she has no physical control over this process, but the changes are initiated by light! It is the lengthening of the day in the spring that triggers hormonal changes within the body, kick starting the reproductive period. Then, if she is pregnant by the time fall comes around, the shortening days will trigger the start of anestrous, so she does not cycle during the winter months.
When a mare becomes pregnant, the reproductive cycle also stops, and hormonal changes occur that alter the physiology of the reproductive system. This is termed the gestational period, and the mare will not cycle again until after the foal is born.
Why Are Lights Used To Alter The Estrous Cycle Of Horses?
In domesticated horses, some breeders use artificial lights to alter the breeding cycle of horses. By gradually extending the length of the day, the hormonal system of the mare can be tricked into thinking it is spring, kick-starting the breeding cycle earlier than normal. This is normally started in the middle of winter and will enable the mare to start cycling by early spring.
The reason for doing this is that it brings forward the earliest time a mare can be mated, and also extends the breeding season. When a mare is mated early in the spring, her foal will be born earlier the next year. In some circumstances, this can be a huge advantage, although early foals do need more care to nurture through the colder months.
Putting a mare under lights also reduces the tricky period where she is cycling irregularly. This can be a problem in maiden mares, making it difficult to assess when they are ready to be mated.
Summary – Light Effects On Estrous Cycle In Horses
So, as we have learned, light effects on estrous cycle in horses triggers the mare to begin her reproductive cycle in the spring. The lengthening days stimulate the hormonal system to start producing reproductive hormones, that cause physical and behavioral changes in the mare. In domesticated horses, artificial lights are sometimes used to stimulate a mare to start cycling earlier in the breeding season.
We’d love to hear your thoughts on the light effects on estrous cycle in horses! Do you have a mare that comes into season at odd times of the year? Or perhaps you’ve got some questions about the best time to breed your mare? Leave a comment below and we’ll get back to you!
What Does Light Influence In Female Horses?
When the mare receives less light in the fall, the brain starts to produce a hormone called melatonin. This suppresses ovarian activity, enabling the mare to into anestrous for the winter.
How Does Light Affect The Estrous Cycles Of The Mare?
In the spring, lengthening days mean that the brain stops producing so much melatonin. This happens gradually, and as melatonin levels decrease the reproductive cycle will resume.
How Long Should A Mare Be Under Lights?
In the northern hemisphere, mares are normally put under lights in early December. The lights should be left on in the evening, with the time gradually increased to give 14 to 16 hours of daylight. The mare should then be cycling normally by mid February.
Do Pregnant Mares Need To Be Under Lights?
Some studies have shown that early foaling mares will benefit from being under lights for the last trimester of their pregnancy. This stimulates growth hormones that help the development of a healthy foal, as well as the production of milk from the dam. Lights may also improve the chances of the mare cycling normally after the foal is born.
Kate Chalmers is a qualified veterinary nurse who has specialized in horse care for the vast majority of her career. She has been around horses since she was a child, starting out riding ponies and helping out at the local stables before going on to college to study Horse Care & Management. She has backed and trained many horses during her lifetime and competed in various equestrian sports at different levels.
After Kate qualified as a veterinary nurse, she provided nursing care to the patients of a large equine veterinary hospital for many years. She then went on to teach horse care and veterinary nursing at one of the top colleges in the country. This has led to an in-depth knowledge of the care needs of horses and their various medical ailments, as well as a life-long passion for educating horse owners on how to provide the best possible care for their four-legged friends.
Kate Chalmers BSc (Hons) CVN, Dip AVN (Equine) Dip HE CVN EVN VN A1 PGCE