How to improve the fertility of mares?

Every year in spring, as the days get longer, mares start to have their monthly cycles again and enter their reproductive period. Some mares will be more sensitive to these changes than others, presenting discomfort, pain and/or unpredictable behaviour, making them difficult to handle. For broodmares, again, not all mares will have equal fertility levels, but there are solutions that can improve fertility.

From the age of two until the end of their lives, mares go into heat in spring, after the winter period, called "anoestrus" when the reproductive system is at rest. The lengthening of the days has an impact on the reproductive hormones of the mares. Longer exposure to light generates a positive action on a part of the brain called the pineal gland, which slows the secretion of melatonin – the sleep hormone – and the hypothalamus produces more GnRH (Gonadotropin Releasing Hormone), a hormone that stimulates the ovaries. This means that the reproductive cycle can begin.

From March to October, the cycles last about twenty-one days. Two phases follow one another: oestrus and dioestrus. During the dioestrus phase, which lasts about sixteen days, a corpus luteum matures on the ovary and produces progesterone, a hormone that prepares the uterus for pregnancy. After about 16 days, if the mare is not pregnant, the uterus sends a signal to the ovary to destroy the corpus luteum and stop producing progesterone. In response, there is a strong production of oestrogen, which will trigger the oestrus, the follicular growth phase with ovulation.

It is during this period, which lasts about five days, that the mare is fertile. During this phase, commonly called "heat", the cervix opens up in response to the increase in oestrogen.

The mare's immunity is strengthened, and the uterus is prepared to combat infection from any germs introduced during insemination or natural mating. Nature knows what it's doing! The mare generally ovulates on day 4 of oestrus. When the egg is released, it descends into the uterus to meet a spermatozoon and form an embryo. If conception occurs, the embryo descends to lodge in the uterus and sends a signal indicating its presence. In this case, the uterus will not send the signal to the ovaries to destroy the corpus luteum. The corpus luteum will remain intact and continue to produce progesterone. The oestrus will stop and the pregnancy will go to term.

Poor nutrition, lack of natural sunlight, excessive exercise, high stress (e.g. transportation), or genetic causes can adversely affect the fertility of mares. Some mares may react negatively to changes in ovarian hormone levels, which can lead to irritability, especially due to pain or discomfort. Difficult, moody and temperamental are all words that are used to describe mares when their behaviour is inappropriate or unpredictable.

Fortunately, there are some simple steps that can be taken to promote the fertility of mares. Nutrition is the basic key to healthy, happy mares and, therefore better fertility. Mares need a certain amount of fat, especially good cholesterol, to produce sexual hormones. Moreover, being outdoors promotes well-being, reduces stress, and provides better access to natural light, needed for the reproductive cycle. Finally, natural solutions, such as food supplements, can also help mares cope better with oestrus and increase fertility by supporting their natural reproductive system.