PPID OR CUSHING'S DISEASE IN HORSES AND PONIES

RECOGNISE EARLY SIGNS OF PPID (OR CUSHING'S DISEASE) IN YOUR HORSE AND PONY


Valerie De Clerck, Doctor of veterinary medicine




Pituitary Pars Intermedia Dysfunction or PPID is the most common hormonal disorder in horses. It is more common in senior horses: 1 in 5 horses over 15 years suffers from this disorder. PPID used to be called Cushing's disease, after a similar disease in humans. As there are some differences between Cushing's disease in humans and horses, we now speak of PPID in horses (1).

IN A NUTSHELL


1. In PPID, the pituitary gland in the brain produces excessive amounts of the hormone ACTH.

2. The risk of PPID increases in horses over the age of 15.

3. The clinical signs of PPID are often mistakenly viewed by owners as normal aging signs.

4. Horses with PPID have an increased risk of laminitis.

5. PPID cannot be cured, but you can balance the hormones with medication and natural supplements.


WHAT IS CAUSING PPID (OR CUSHING'S DISEASE) IN HORSES AND PONIES?


PPID in horses is as complicated as the name itself, and even scientists do not exactly know how the disease originates. However, they do know that the brain's pituitary gland produces excessive amounts of hormones, including the hormone ACTH.


Once sufficient amounts of hormones have been produced in a healthy horse, the hypothalamus will tell the pituitary gland to stop making more. In PPID, these "brake cables" or nerve fibers are damaged, failing the hypothalamus to communicate with the pituitary gland. So, the pituitary gland just continues to produce large amounts of hormones, with all its consequences.


Hormones from the pituitary gland stimulate the adrenal gland to produce and secrete the stress hormone cortisol. Cortisol regulates the sugar and fat metabolism in the body. In horses with PPID or Cushing's disease, the total amount of cortisol in the blood is not elevated, but there is an increased local activity of cortisol within the tissues. It is this high local activity that largely explains the clinical signs of PPID (2,3).


Figure 1: the production of ACTH and cortisol in the body of the horse

WHAT ARE THE SYMPTOMS AND SIGNS OF PPID (OR CUSHING'S DISEASE) IN HORSES AND PONIES?


Many owners find it hard to recognize PPID or Cushing's disease in their horses, as the symptoms of PPID are often mistakenly considered normal aging signs. The most common symptoms of PPID in the horse are (1):


•  abnormal hair growth (usually a long curly coat);

•  delayed or inappropriate shedding in spring and summer;

•  loss of muscle mass (especially along the topline);

•  laminitis;

•  abnormal fat deposits: "potbelly" and above the eyes;

•  excessive sweating;

•  excessive drinking and urinating; and

•  lethargy.

HOW CAN I TEST IF MY HORSE OR PONY IS SUFFERING FROM PPID (OR CUSHING'S DISEASE)?

Do you recognise any of the symptoms of PPID or Cushing's disease in your horse or pony? Then you should always contact your veterinarian. Your vet can test via a blood test whether your horse has PPID.


The level of ACTH is measured in the blood. In horses with PPID, the level of ACTH is elevated. The ACTH concentration varies according to the time of the year and should be considered when interpreting the results.


When is the ACTH level in the blood of my horse or pony too high?


From mid-July to mid-November (summer & autumn)

•  Negative  < 11 pmol/L

•  Grey zone: 11 – 22 pmol/L

•  PPID positive  > 22 pmol/L (100 pg/mL)


From mid-November to mid-July (winter & spring)

•  Negative  < 6.6 pmol/L

•  Grey zone: 6.6 – 11 pmol/L

•  PPID positive  > 11 pmol/L (100 pg/mL)


In mild cases of PPID, there may be no obvious increase in ACTH levels. In that case, your veterinarian can perform a second and more sensitive test: the TRH stimulation test (1). 

TREATMENT AND MEDICATION FOR PPID (or CUSHING's DISEASE) IN HORSES AND PONIES


PPID in horses or ponies cannot be cured because the damaged nerves cannot be repaired. But with suitable management and treatment, it is possible to balance the hormone production and to reduce symptoms of PPID so that your horse or pony can continue to live happily and active for a number of years.


The only recognized medication currently on the market for horses with PPID is Prascend, with pergolide as the main active ingredient. Through stimulation of dopamine receptors, Prascend has a suppressive effect on the pituitary gland, which decreases hormone production (ACTH) and reduces symptoms of PPID. The side effect of Prascend is that it can have a negative effect on the mood of your horse by interfering with the production of other hormones. Not infrequently, owners report that their horse appears depressed after starting with Prascend. Typical side-effects are loss of appetite and lethargy.

You can also offer your horse or pony with PPID additional nutritional support with a plant-based supplement. 


METABOLIC CARE is a combination of 7 plants, L-arginine and Chlorella (algae), with a supportive effect in different areas.


1. Supports the natural defense system thanks to MSM, horsetail (Equisetum arvense), and milk thistle extract (Silybum marianum).


2. Supports the liver and regulates sugar- and fat metabolism.


Milk thistle (Silybum marianum) is an excellent herb to support the liver and also has a balancing effect on sugar and fat metabolism. These properties are also attributed to the superfood Chlorella, a miniature algae rich in vitamins and minerals (4). The name suggests otherwise, but licorice extract (Glycyrrhiza glalbra) has a lowering effect on ACTH levels and protects the stomach (5,6). Chrysanthellum Americanum has a protective effect on the liver and intestines and stimulates blood circulation (7,8). Sourberry (Berberis vulgaris) has a regulatory effect on blood sugar levels and supports intestinal flora (9,10).


3. Strengthens the connective tissue in the laminae of the hoof thanks to the supply of silica in Equisetum (7). MSM is very rich in sulfur, the most important mineral in the hoof wall. 


4. Promotes blood flow in the feet thanks to L-arginine, maritime pine (Pinus maritima), and Chrysanthellum americanum (11,13).



SCIENTIFIC REFERENCES


1. McGowan CM. EquineCushing'ss Disease/PPID - what do we know now? In: Proceedings of AVA Annual Conference, Brisbane. ; 2018.

2. Morgan RA, Keen JA, Homer N, et al. Dysregulation of cortisol metabolism in equine pituitary pars intermedia dysfunction. Endocrinology. 2018;159(11):3791-3800. doi:10.1210/en.2018-00726

3. Hofberger SC, Gauff F, Thaller D, Morgan R, Keen JA, Licka TF. Assessment of tissue-specific cortisol activity with regard to degeneration of the suspensory ligaments in horses with pituitary pars intermedia dysfunction. Am J Vet Res. 2018;79(2):199-210. doi:10.2460/ajvr.79.2.199

4. Ebrahimi-Mameghani M, Sadeghi Z, Abbasalizad Farhangi M, Vaghef-Mehrabany E, Aliashrafi S. Glucose homeostasis, insulin resistance and inflammatory biomarkers in patients with non-alcoholic fatty liver disease: Beneficial effects of supplementation with microalgae Chlorella vulgaris: A double-blind placebo-controlled randomized clinical trial. Clin Nutr. 2017;36(4):1001-1006. doi:10.1016/j.clnu.2016.07.004

5. Al-Qarawi AA, Abdel-Rahman HA, Ali BH, Mougy SA El. Liquorice (Glycyrrhiza Glabra) and the Adrenal-Kidney-Pituitary Axis in Rats.; 2002. www.elsevier.com/locate/foodchemtox.

6. Luca S, Enrica Z, Alessia S, et al. Efficacy of the Administration of a Natural Feed Supplement in the Management of Equine Gastric Ulcer Syndrome in 7 Sport Horses: A Field Trial. Am J Anim Vet Sci Orig Res Pap. 2017. doi:10.3844/ajavsp.2017

7. Verhelst G. Great Handbook of Medicinal Plants; 2018.

8. Cojocariu R, Ciobica A, Balmus IM, et al. Antioxidant Capacity and Behavioral Relevance of a Polyphenolic Extract of Chrysanthellum americanum in a Rat Model of Irritable Bowel Syndrome. Oxid Med Cell Longev. 2019;2019:3492767. doi:10.1155/2019/3492767

9. Hu X, Zhang Y, Xue Y, Zhang Z, Wang J. Berberine is a potential therapeutic agent for metabolic syndrome via brown adipose tissue activation and metabolism regulation. Am J Transl Res. 2018;10(11):3322-3329.

10. Wang H, Zhu C, Ying Y, Luo L, Huang D, Luo Z. Metformin and berberine, two versatile drugs in treatment of common metabolic diseases. Oncotarget. 2018;9(11):10135-10146. doi:10.18632/oncotarget.20807

11. Iravani S, Zolfaghari B. Pharmaceutical and nutraceutical effects of Pinus pinaster bark extract. Res Pharm Sci. 2011;6(1):1-11. http://www.ncbi.nlm.nih.gov/pubmed/22049273%0Ahttp://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=PMC3203267.

12. Siani A, Pagano E, Iacone R, Iacoviello L, Scopacasa F, Strazzullo P. Blood pressure and metabolic changes during dietary L-arginine supplementation in humans. Am J Hypertens. 2000;13(5):547-551. doi:10.1016/s0895-7061(99)00233-2

13. Baxter GM. Alterations of Endothelium-Dependent Digital Vascular Responses in Horses Given Low-Dose Endotoxin. Vet Surg. 1995;24(2):87-96. doi:10.1111/j.1532-950X.1995.tb01301.x


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