Blood Results - A bit of a surprise.

Within a couple of days we received the results from Archie's free seasonal ACTH test for Cushings disease and his insulin and glucose levels from his dynamic insulin response test. The reason for performing these tests was to evaluate Archie's current laminitis risk status, as discussed in our earlier blog post.

Due to the excellent management by Archie's owner, Fran, we found that Archie had normal glucose and insulin levels following his meal of glucose powder in chaff. Indicating that Archie is regulating his insulin levels appropriately, when faced with sugars, such as those found in grass.

The fact that Archie is carrying larger fat deposits than normal, but is currently regulating his insulin efficiently indicates that the current feed restrictions and management practices are working to tell Archie's body that he is in a negative energy balance and he needs to metabolise those fat stores.

Insulin resistance occurs naturally in the majority of UK native breeds, as they gain body fat they become more insulin resistant, leading to higher circulating levels of the hormone insulin. High insulin levels trigger the body to store fat in deposits rather than break it down. This would allow these native breeds to store fat whilst grass was available and therefore to survive through cold winters with poor sparse grazing. However our local native breeds are far from facing exteme feed shortages or snow covered fells, this cycle of insulin resistance triggering further fat deposition, causing increasing insulin resistance, is a difficult cycle to break. High levels of the circulating hormone insulin can directly trigger laminitis in otherwise healthy horses (De Laat et al, 2010).

Welsh ponies and other native breeds such as these, are naturally insulin resistant. 

The second part of Archie's results revealed a bit of a surprise. Archie's ACTH value was 41pg/ml, normal being <29pg/ml for this time of year. This indicates that Archie has evidence of Pars Pituitary Intermedia Dysfunction, more commonly referred to as Cushing's disease.

Archie is currently not showing symptoms of Cushing's disease. We know the disease is very common in horses over 15 years of age and we believe it starts to occur quite some time before it is detectable on ACTH tests. In horses that show symptoms of Cushing's disease, but have a normal ACTH reading a more sensitive test known as a TRH stimulation tests can be performed to pick up early cases.

The symptoms of Cushings disease are mild to start with and include a loss of topline muscle, a pot belly appearance and fat deposits in the hollow above the eye. Delayed hair shedding or long guard hairs are often seen. Increased drinking, sweating and lethargy can develop. The disease causes suppression of the immune system leading to increased worm burdens, gum disease, delayed healing of wounds or corneal ulcers and recurrent respiratory infections. The disease can also lead to hyperinsulinaema and laminitis. Horses can develop both Cushing's disease and Equine Metabolic Syndrome, the combination of which leads to a high laminitis risk.

As Archie is full of beans and not showing current symptoms of the disease he will be monitored with a follow up blood test during the Autumn, when testing of ACTH is even more accurate. Archie's owner will be monitoring him closely for any of the clinical signs mentioned and when neccesary Archie will be able to start treatment with pergolide tablets to restore normal ACTH levels and counteract the symptoms of disease. The diagnosis does not alter Archie's current management or his ability to continue with rehabilitation and return to eventing.

Reference

De Laat et al (2010) Equine laminitis: induced by 48 hour hyperinsulinaemia in standardbred horses. Equine veterinary journal 42 129-135