Colic and oestrus - is there a connection?

By Dr. Kai Kreling, Binger Wald Veterinary Clinic, Waldalgesheim (Germany)

The digestive system of the horse is a highly complex system. Hard-to-digest feed components can be very efficiently converted into digestible substances in the horse as a herbivore. This takes place in a very long gastrointestinal tract of up to 30 metres. Millions of intestinal bacteria are very powerful assistants in the process. The prehistoric horse needed such a specially adapted digestive system. It subsisted on sparse steppe grass that was low in energy. It had to eat huge quantities of this grass to cover its nutritional requirements. Horse feed rations today consist of high-quality, high-energy feed components. The functions and bacteria in the intestine are not used in the original way.

This leads to the increased susceptibility to colic/stomach ache in horses.

Nutrition is not the only thing that impacts on the digestive system. Cardiovascular problems lead to poor blood circulation in the gastrointestinal tract. This in turn leads to reduced intestinal movement and poses a risk of constipating colic. Stress, ulcers and gastrointestinal tumours are other possible causes of colic.

Many stud owners are familiar with the problem when their mares are in oestrus. Here, too, mild colic symptoms may manifest. In the course of the cycle, the mare's ovaries undergo changes in a specific chronological order.

These are controlled by hormones. Spring and summer are the main periods of activity. This may be one reason why mares show colic symptoms in spring with the onset of cycle activity. The average cycle in mares is 21 days. The cycle is the time between two ovulations. On the ovary, the follicles that contain the eggs ripen. Ovulation takes place in the last 24-48 hours of oestrus. The ovum then passes through the fallopian tube into the uterus. After ovulation, a so-called corpus luteum is formed at this point on the ovary. First, the follicle cavity fills with blood (= corpus haemorrhagicum). The corpus luteum, the yellow body, then develops from the corpus hemorrhagicum. The follicle phase lasts 5-7 days, the corpus luteum phase 14-15 days. Mares can have colic symptoms throughout the follicle phase. It is advisable in such cases to have the mare examined to see if it is normal cycle activity or not. Extreme follicle maturation can often be felt rectally by the veterinarian, without aids. With the help of ultrasound, regular follicle maturation can usually be distinguished from atypical follicle development.

In the horse, the peritoneum covers the ovary. If a follicle matures and reaches an extreme size, the peritoneum is stretched quite tightly over the ovary. In individual cases this leads to increased sensitivity and also to colic symptoms. Tumours can also form on the ovary. Different types of tumours on the ovary of the mare may be associated with colicky behaviour. A tumour can result in the ovary attaching or, simply because of its size, may be a hindrance to intestinal peristalsis. Haematomas (bruises) or abscesses can also occur on the ovary and may be associated with colic behaviour. Changes in the uterus area, however, are generally not associated with colic behaviour. If all of these examinations do not produce any findings, the mare can be given an artificial hormone, a progesterone, over a certain period of time. This suppresses oestrus. If the colic stops, there is definitely a connection between cycle activity and colic behaviour.

Colic is a disease of which the cause is often very difficult to fathom. Appropriate care and nutrition are very important. Regular feeding combined with sufficient raw fibre content are essential for a healthy horse. Water is very important for the horse, as for other creatures. In summer on the pasture, or even more importantly in a truck or trailer on the way to a competition, horses need large quantities of water. Too little water leads to cardiac and circulatory strain and also to drying out of the contents of the stomach and intestine. In addition to proper nutrition, every horse should get enough exercise every day. Movement stimulates the bowel functions. Not to forget the regular biannual / annual dental check. If there are problems with their teeth, horses don't chew the feed finely and the danger of colic increases.

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