Q. My daughter’s Quarter Horse mare tested for PPID last fall, so this is my first spring managing her with this diagnosis. What can I do from a dietary standpoint to keep her healthy?
A. I work with a lot of horses that have pituitary pars intermedia dysfunction (PPID, formerly called equine Cushing’s disease), and the good news is horses with this condition can lead very happy, active lives when it is well-managed, so I applaud you for wanting to be proactive. When I think spring management of horses with endocrine disorders, I immediately think pasture and grass and, from there, my concerns go to laminitis. Endocrinopathy is the predominant cause of laminitis, which for some horses can become a death sentence.
Recent research has shown that ponies with an insulin level above 45 have a 70% chance of developing laminitis. These are typically the individuals that have some kind of insulin dysregulation (ID). Not all horses with PPID also have ID, so my first recommendation is if you do not know whether your horse also falls into the category of being ID, talk to your vet about doing the bloodwork necessary to make the diagnosis. This way, you will have a better understanding of how careful you must be in regulating nonstructural carbohydrate intake.
PPID is not managed through diet; rather, it is managed with medication (pergolide), but ID and equine metabolic syndrome—which some PPID horses also have—are managed by diet and exercise. If you have not retested adrenocorticotropic hormone (ACTH) levels since the initial diagnosis, I would suggest doing this at the same time to confirm the medication dose being given is correct.
Once you know whether your mare is insulin dysregulated in addition to having PPID, you will be able to make informed decisions about how best to manage and feed her. If she has ID, I would strongly caution against allowing access to pasture. If her insulin values are normal, you can provide careful access to pasture. Consider the use of a grazing muzzle that will allow access but limit total intake. Monitor her weight closely, and body condition score her regularly to identify the onset of fat deposits. Take prompt action to keep her at an ideal weight before things get too far out of hand.
What To Feed the PPID Horse
While diet is not directly used to manage PPID, diet and nutritional management go a long way in helping support these horses. Not all horses with PPID are overweight; in fact, some struggle to maintain good topline and appear to be too lean. Providing a source of quality protein in the ration can be of particular benefit for these individuals. If overall weight is good with only forage but topline is lacking, a high-protein ration balancer is a good choice.
For those horses that are generally struggling to maintain weight, finding and adding a low nonstructural carbohydrate senior feed to their diet is a good choice. I also strongly recommend having a qualified dental specialist examine these horses’ teeth carefully, as I have worked with a number of PPID horses that also have equine odontoclastic tooth resorption and hypercementosis (EORTH). This condition can be missed and had previously been missed in one client’s horse, leading to significant discomfort and weight loss.
Another cause of decreased body condition in this population of horses is internal parasites. Horses with PPID are at greater risk of having higher internal parasite burdens than healthy horses without PPID. (Editor’s note: Another study on FECs in preclinical PPID horses had differing results, though FECs decreased with pergolide treatment.) Monitor fecal egg counts to determine whether your horse might have higher than normal numbers and whether your deworming protocol is effective.
How To Manage My PPID Horse’s Going Forward
Continue to monitor bloodwork over time so you can make diet adjustments as necessary. In particular, retest ACTH in late summer to ensure management strategies are working well before the seasonal peak in ACTH occurs in early fall.
Through careful monitoring of ACTH and insulin values you will be able to make good management decisions for your daughter’s mare and give them the best chance of living many more happy years together.