After writing a post on the hormone leptin the other day (click here), I decided to write a post on insulin resistance in horses. Insulin and leptin have also been found to be linked. I have got my endocrinology module exam tomorrow so this is my last bit of revision on hormones.
Insulin is a hormone that is released by the pancreas. If helps to bring the glucose levels down in the blood by putting the glucose into storage and preventing the body from absorbing more. This is important as you do not want the levels to get too high.
Insulin resistance in the horse has been linked to a number of other diseases such as developmental orthopaedic disorders, laminitis , equine metabolic syndrome and Cushing's disease.
Insulin resistance is seen in humans in the form of diabetes. Type 1 diabetes is from a young age and patients have a problem with their pancreas as it is not producing insulin. They will have high levels of glucose in the blood after they have eaten a meal.
Type 2 diabetes develops over time and is often seen in obese people. They will also have raised blood glucose levels but this is due to a high energy diet. The pancreas tries to compensate for this by producing more insulin but over time they will become de-sensitised to these high insulin levels. The pancreas can also stop working in some cases.
In animals, insulin resistance has been linked to foods with a high glycaemic index (GI), these are food that make the blood glucose levels raise more after eating them.
Animals can suffer from both types of diabetes but it is usually the type 2 form seen in fat horses and ponies. It is most commonly seen in native breeds. It has been found that small ponies have higher levels of circulating insulin levels than larger horses. Obesity increases insulin resistance and exercise will decrease it. Click here to be taken to a fact sheet on insulin resistance produced by thehorse.com which are an online guide to equine health care, it talks about the symptoms and treatments which I will not be talking about here.
There are a number of methods to test glucose resistance which I have learnt for my exam but I am not going to go through them here. If you would like more information then let me know.
Sessions et al (2004) looked at the effect insulin resistance had on the oestrous cycle in mares. It was concluded that the condition may modify characteristics of the oestrous cycle, perhaps at the level of the ovary.
Treiber et al (2006) found that insulin resistance was linked to laminitis. Therefore characterising insulin resistance may help with the management of ponies to avoid laminitis and potential strategies to use such as reducing obesity, increasing exercise and moderating dietary carbohydrates, particularly starch.
Hyperlipaemia is linked to insulin resistance. This is a condition seen in horses when they go into a negative energy balance (they are using more energy than they have coming in from their feed). It is often seen in small, over weight ponies. Stress can also increase the likelihood of the condition, but the condition causes stress causing a viscous circle.
I first came across this condition when I was working at the Donkey Sanctuary. Donkeys often form strong attachments to another donkey and they told me if they were separated they could get stressed. This caused the donkeys to stop eating and their body would have to release fat to use as an energy supply. However, their body would keep releasing the fat and in the end it could be a fatal condition. Here is an information sheet produced by the Donkey Sanctuary on the disease. I had never heard of this condition in the horse before this module.