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Cushings syndrome

Let’s Talk About Cushing’s syndrome with Dr Tom Shurlock, British Horse Feeds consultant nutritionist

Q1 – What is Cushing’s Syndrome or Pituitary Pars Intermedia Dysfunction (PPID)?

It is an endocrinopathic disorder (hormone dysfunction), mainly affecting older horses. A portion of the brain, the hypothalamus, loses its ability to inhibit dopamine (a neurotransmitter), and this results in excessive, sometimes abnormal growth of the pituitary pars intermedia and an increase in the secretion of hormones and hormone-like factors from the pituitary gland. These include α- MSH and ACTH, which results in the commonly recognized clinical signs of PPID.

Α-MSH activates piment production in the skin. ACTH increases the release of cortisol from the adrenal glands; additionally, a free cortisol faction (FCF), found in obese animals, is elevated in PPID horses – possibly due to compromised cortisol binding – and is thought to lead to insulin dysregulation (hyperinsulinaemia), resulting in IR.

One of the characteristics of PPID, both in equines and humans, is the presence of inflammatory cytokines. Non-specific inflammation can lead to a number of disorders and increases the likelihood of developing EMS. Inflammatory responses also affect circulation, insulin sensitivity and amino acid metabolism and protein function. A disruption of normal dietary metabolism increases oxidative stress which further impacts on pro-inflammatory factors.
Q2 – What are the signs of Cushing’s?

The most obvious symptom of Equine Cushing’s is a hairy coat. Insulin dysfunction, coupled with cortisol production causes an increase of amino acids into protein and the dysfunction of the melanocytes results in a paler coat. At the same time, diversion of amino acids to hair production can lead to muscular wastage, weight loss and pot bellies. The hormonal disruption leads to symptomatic fat deposits, cresty neck etc., as well as increased appetite and water intake.

Cortisol dysfunction also affects the kidneys resulting in higher urinary output, whilst the dopamine interaction leads to lethargy, docility and behavioural changes.

Finally, non-specific inflammation and insulin resistance can increase the incidence of laminitis.

Q3 – Nutrition wise, what can owners do if they have a horse or pony with Cushing’s?

There are two areas to concentrate, supplying energy that does not compound insulin resistance which should help restore amino acid and fat metabolism, and to help reduce oxidative/inflammatory stress. There is, of course, veterinary treatment and this may involve the reduction of glucose absorption, drugs to increase metabolism, or the use of dopamine agonists to help reset the pituitary gland. However, these treatments do not impair the nutrition of the Cushing’s horse, which centres on the reduction of NSC (non-structural carbohydrates) intake.

The horse is supremely adapted to eating fibre and supplying energy in the form of sugar and starch puts a strain on the insulin dependant pathways. As PPID also stresses these, reduction of dietary sugars is beneficial. Fibre is fermented in the hindgut producing slow release energy in the form of volatile fatty acids that are absorbed and enter the energy generating metabolic pathway without inducing insulin release. A lower insulin impacts on both protein and fat metabolism, helping restoration to normal levels. Once the majority of energy is supplied this way and energy intake can be increased by the introduction of super fibres (Speedi-Beet, Fibre-Beet), the knock on effect means selective protein sources can be added that are suited to help regenerate skeletal muscle.

When considering the interaction between hormonal control, reactive inflammatory responses and oxidative parameters, it is essential to consider the role of the cardiovascular system. Many of the effects of the responses impact directly on blood flow, from arterial relaxation by insulin and NOX, leading to hypoxia, to the release of amines, influencing blood pooling and build-up of negative factors. Maintaining a healthy and rigorous blood flow is a major step in helping to support optimum parameters in the oxidative/inflammatory cycles and potential insulin dysfunction. Feeding antioxidants that interact with oxidative enzymes such as NOX, and plant polyphenols have a role to play, can help those mechanisms that reduce non-specific inflammation, and help maintain equilibrium. Providing omega fatty acids also support the structure of the cardiovascular system.

Q4 – What about grazing?

The degree of grazing very much depends on the makeup of the grass. Spring grass, for example is notorious for being unsuitable for laminitics, and it is the same criteria that will impact a Cushing’s horse. High levels of fructans and sugars cause disruption in the hind gut which leads to the absorption of endotoxins, inflammatory cues and vasoconstrictors. However, a mature grass – preferably mixed meadow hay – may well be suitable. Grazing has the benefit of keeping the horse moving, which aids blood flow, muscular integrity and gut function; however, if the grass is thought to be too high in sugars, soaked hay can be given. It can be spread across a paddock to gain the benefits of movement.

Q5 – Any top tips for owners?

• The main tip would be to try and keep your horse moving. Gentle exercise is sufficient to make a difference and this can be increased as symptoms decline.

• Secondly do not overfeed. Fat deposition is a side effect of Cushing’s and obesity adds to the cortisol induced dysfunction. Bulking feed with a soft straw can help with diluting the ration. However, if intake is depressed (excessive appetite is not always a symptom of Cushing’s), then introduce a super fibre.

• Most forage and super fibres will have adequate protein, but small amounts of, for example, linseed can be added if condition needs to be improved.

• Consider supplements rich in antioxidants and plant flavonoids. Although these products are increasingly popular for mainstream nutrition, supporting the mechanisms that address oxidation and inflammation can help reduce stress related issues of PPID.