Those Fiesty Mares:
How a Mare's Cycle Can Affect Performance
By Debra Ottier
Iron Horse Equine
You begin your normal daily ride, like so many other days, when your mare decides to be a very unwilling partner. All that work, conditioning and training her, yet sometimes she fights every move you make, pinning her ears back, switching her tail and refusing to do anything you ask of her. She usually is a wonderful mount, but now she seems as stubborn as a mule. Why the change? This situation is common in the horse world and is usually referred to as the "mare" syndrome, but what is it and why does it happen? The underlying reasons for cycle related performance problems are not really understood, but if your mare does act abnormally or is difficult during training exercises, you need to assess the reasons behind this behaviour.
Common signs of this "syndrome" are aggression towards you or other horses, abnormal behaviour, nymphomania, lameness, abdominal and/or back pain and general difficulty while riding. Aggression or nymphomania may be caused by hormone producing tumours on the ovary, the primary reproductive organ of the mare. This can be a major concern, as tumours can affect fertility and may become cancerous. Lameness or back pain may be caused by musculo-skeletal or neurological problems, but can also be due to painful ovaries. When pressure is applied from a rider, some mares may show pain near the ovaries, especially at the time of ovulation. As an egg bearing follicle develops on the ovary, fluid fills into the center which can be painful to some mares. When ovulation occurs, there is a small amount of tissue damage on the ovary resulting in the formation of what is termed a corpus luteum, again resulting in some discomfort to the mare. Abdominal pain is usually associated with the intestinal tract, however, colic like pain has been described in association with ovulation. If it is found that none of these problems are the cause of your mare's behaviour, the problem may be associated with her estrous cycle.
Erratic behaviour may be due to the changes throughout the estrous cycle of your mare, with problems usually seen in the heat portion of the cycle, but may also occur during the non-heat or diestrus period as well. The normal estrous cycle of the mare is approximately 21 days with a period of estrus or heat lasting 5-7 days, and a diestrus period lasting 14-16 days. The estrus period is characterized by frequent urination, teasing of other horses, and general irritability. The major hormone active during this time is estrogen, a steroid which activates the reproductive system to prepare for possible breeding and subsequent pregnancy. This hormone effects the behavioural center as well, causing the mare to become receptive to a stallion, or other horses. While you are riding your mount during the heat phase, your mare has estrogen and other raging hormones throughout her body having an innate hold which, unfortuneatly, is stronger than any command you use.
The major hormone of the diestrus period is progesterone, also known as the hormone of pregnancy. Progesterone prepares the mare for possible oncoming pregnancy by changing the tone of the uterus by reducing edema, and this hormone has a calming effect on the mare's system, subduing ovarian activity. This is why many "hot" mares settle down when pregnant. Prostaglandin is a hormone normally produced in the mare by the uterus to start the estrous cycle over. This hormone will cause contractions of the uterus, resulting in a small degree of colic like symptoms including sweating, kicking at their sides and general discomfort. Other estrous hormones may have similar effects on the mare.
What can you do about this situation? There are hormonal therapies which can be used to manipulate the estrous cycle of the mare. Progesterone is a natural progestogen prepared from the oil of seeds from sesame, cotton or sunflower plants. It is also prepared from polyethylene glycol, to allow for a slow or prolonged release following intramuscular injection. Progesterone therapy has been used to subdue the normal heat cycle and suppress the activity level of the ovary of the mare. The purpose of this treatment is to prolong or extend the estrous cycle by lengthening the diestrus phase. Progesterone has a negative feedback effect on the ovulation hormone called luteinizing hormone (LH), thus preventing ovulation from occurring. Altrenogest or Regu-mate has a high efficacy rate and is very easy to administer, making it the most used form of progesterone therapy available. Estrogens can also be used to suppress follicular growth. The active form used is estradiol -17b which is combined with daily progesterogen and given intramuscularly. Colorado State University is conducting trials for efficacy of other forms of progestogen and delivery systems in suppressing estrus and delaying ovulation. Some foods, herbs and spices have components which mimic the effects of estrogen and progesterone as well as androgens. Some herbs and spices which contain estradiol binding components include soy milk, licorice, red clover, mandrake and thyme. Licorice, mandrake, red clover and thyme also contain progesterone binding components along with oregano and nutmeg.
The long term use of these products has not been shown to have any effect on fertility when they are consequently stopped. It is advisable to discuss diagnosis and treatment with your veterinarian.