⏰ Estimated reading time : 10 minutes
Cushing's disease is very probably caused by a neurodegeneration in the horse's brain, resulting in an exaggerated secretion of certain hormones. One of them, ACTH, would be at the root of numerous symptoms which accompany this disease...
What is cushing's disease in horses?
Cushing’s disease, or PPID: Pituitary Pars Intermedia Dysfunction (the pituitary is also called the hypophysis), is the dysfunction of a small gland situated in the horse’s brain.
⏩ Read more : How to feed the aged horse?
a. What are the warning signs?
The most frequent symptoms are the following: laminitis, obvious hypertrichosis (very long and curly coat), lethargy, muscle wasting, pot belly, and sometimes polyuria-polydipsia (increase in the volume of urines and a permanent and intense sensation of thirst), reoccurring infections and episodes of abnormal transpiration.
These pronounced symptoms are often related to a very advanced stage of the pathology.
Other clinical manifestations can nevertheless appear in an earlier and more subtle way: diminishing sporting performances, drop in fertility, amyotrophy of the top line, small alterations in behaviour, changes in the appearance of hooves and the hoof wall without lameness, slight delay in spring moulting with or without localised hypertrichosis.
Scientific advances in recent years have allowed earlier diagnosis of the disease.
b. How is cushing's disease diagnose in horse?
The diagnosis of Cushing’s Disease rests on measuring the level of the hormone ACTH in the blood (plasma).
⚠️ Knowing that intense physical exercise, a moderate to serious illness, or intense pain can increase the plasmic ACTH concentration, the results should be interpreted taking into consideration the clinical context.
⚠️ In addition, the basal plasmic ACTH concentration shows seasonal variation in all horses. Recently collected data on a very large number of individuals suggested that the period of increased production of ACTH is triggered by the summer solstice and extends from July to November included. It is the same for horses suffering from PPID.
Additional studies have permitted to establish seasonal reference ranges thus permitting the ACTH concentration test to be used throughout the year to diagnose Cushing’s disease. Furthermore, it has been demonstrated that autumn would be the most opportune moment to test your horse. Indeed, it is during this season that the basal plasmic ACTH concentration test shows the most sensitivity and precision.
Next, the quest for more accuracy in testing outside of this autumnal period has led to the development of another diagnostic test.
[THE TRH STIMULATION TEST]
The TRH (thyrotropin-releasing hormone) stimulation test allows a diagnosis of PPID to be established with even greater accuracy than the basal plasmic ACTH concentration test.
⚠️ Finally, it is important to note that insulin resistance is frequently present in horses suffering from PPID. Therefore, glucose-insulin parameters should be taken into account in the complete assessment of the PPID horse as well as in his subsequent nutritional management.
c. What treatment is given to horse suffering from cushing's disease?
There exists today effective medical treatments allowing to limit the progress of the disease.
Your veterinary surgeon will be able to advise you on the setting up and the monitoring of the treatment.
✅ It’s appropriate to take stock of the rest of the parameters which can affect the horse’s health: vaccine status, dental health, worming, liver or kidney diseases.
✅ Putting into place suitable environmental measures (if the horse lives in a group) can also be beneficial:
- Separate the horse to feed him,
- Pay particular attention to the group hierarchy,
- Make sure that the horse manages to feed if he is low ranking within the herd.
How to feed horse suffering from cushing's disease?
1️⃣ - The horse suffers from cushing's disease without clinical signs
If a horse at rest, in good condition, shows clinical signs of PPID without ever having suffered from laminitis, supplying him with good quality forage (grazing and/or hay) in sufficient quantitycan be enough to cover his requirements in energy (feed about 2% of bodyweight in kg in hay).
⚠️ However, it’s important to analyse your hay in order to know its soluble sugar levels. (Soluble sugars are simple sugars such as glucose, fructose, sucrose, maltose, and fructans. They are digested in the small intestine and their absorption influences the horse’s glycaemic response).
It is possible to send a hay sample to the Reverdy Laboratory with a view to carrying out an analysis of the analytical constituents.
Providing a vitamin and mineral supplement or a vitamin and trace element based supplement such as Reverdy OLIGOVIT MINERAL, is recommended in this case to ensure satisfactory cover of daily requirements of these nutriments, more or less partially, deficient in most forage.
2️⃣ - The horse suffering from cushing's disease, starts to lose muscle mass
For horses lacking muscleand/or receiving a forage with poor protein levels, it’s preferable to give the hay corrector CEREAL FREE, which in addition to vitamins and trace elements, provides quality proteins rich in essential amino-acids, as well as omega 3s and postbiotics (lactic ferments) advantageous to maintaining good digestive and metabolic health.
3️⃣ - The horse suffers from cushing's disease with poor body condition and muscle wasting
If in addition to having muscle wastage the horse is thin, feeding a higher energy complementary feed (as well as making hay available ad-lib) facilitates the recovery of condition. In this case, it is advisable to favour feeds essentially constituted from fats and fibres. These latter may equally contain low quantities of cereals, sources of complex carbohydrates (starch).
✅ It is recommended to not exceed 30g of starch for 100kg of bodyweight per meal and to favour “slow” sources such as barley whose starch is less digestible than that found in oats, wheat or cereal flakes.
❌ Feeding with cereal flakes is highly inadvisable.
❌ Feeds containing molasses are to be prohibited as this ingredient is high in simple sugars (saccharose = white sugar) likely to aggravate the resistance to insulin often found in horses suffering from Cushing’s Disease.
Reverdy proposes ADULT SPECIFIC ENERGY, a pelleted feed low in starch, enriched in fats and fibre.
[RECOVERING BODY CONDITION]
In complement to this diet, it is recommended to add pre/pro/post-biotics. Indeed, these latter contribute to improved working of the gut flora which is notably characterised by an improvement in the digesting of fibre and thus a gain in condition.
Reverdy FLORE is an association of probiotics and postbiotics supporting the gut flora.
4️⃣ - The horse suffers from cushing's disease and chronic laminitis
For horses prone to laminitis, restricting carbohydrates is of even greater importance.
- For starch, the maximal threshold to not exceed is 15g for 100kg bodyweight per meal.
- For forages, the highest acceptable level of soluble sugar is 10% of dry matter (DM).
On the subject of pasture, it is recommended to limit access to grass during the periods where there is a large accumulation of soluble sugars, that is: at the beginning of spring and at the end of autumn, after periods of drought or frosts, sunny cloudless days following a cold night (< 5°C).
Finally, it is advisable to soak hay in water for 2 hours before feeding in order to eliminate a proportion of the soluble sugars.
[TO GO FURTHER...]
To finish, supplementing with vitamins C and B12 seems pertinent.
In fact, a number of studies have revealed that horses suffering from Cushing’s/PPID will be deficient in vitamin C. Now, this latter plays a vital role in immunity which drops with age and the hormonal imbalances observed in these horses. That’s why, it is advisable to supplement horses suffering from Cushing’s Disease with vitamin C at a level of 1 to 2 gr/day – up to 10g/twice a day.
Finally, a recent study (March 2020) showed that horses suffering from Cushing’s Disease/PPID will also be deficient in vitamin B12. This vitamin plays an essential role in the normal functioning of the brain and central nervous system.
Consequently, even if further investigations must still be carried out in the equine species, fortified supplementation in vitamin B12 for horses suffering from Cushing’s disease seems pertinent.
Reverdy feeds that are suited to horses with Cushing’s/PPID have fortified levels of vitamin B12 and even vitamin C (ADULT SPECIFIC ENERGY).