Promoting Metabolic Wellness
Horses with equine metabolic syndrome usually have fat deposits over the ribs, withers, and buttocks, a cresty neck, and evidence of other abnormalities associated with laminitis development.
Equine metabolic syndrome and Cushing's disease prevention start from birth and include regular veterinary exams and proper nutrition.
By the time most owners start talking about equine metabolic issues, their horses have already developed a problem. But what if we could take a more proactive approach by feeding and monitoring our horses to curtail metabolic disease development in the first place? Much like we use vaccines and biosecurity measures to prevent infectious disease, we might be able to forestall metabolic disease with nutrition and overall wellness strategies.
Nick Frank, DVM, PhD, Dipl. ACVIM, professor of large animal internal medicine and chair of the department of clinical sciences at Tufts University’s Cummings School of Veterinary Medicine, is a pioneer in equine metabolic disease research. He suggests owners take a proactive approach to managing metabolic issues such as equine obesity and insulin dysregulation (excessive insulin response to oral sugars, evident as postprandial hyperinsulinemia, fasting hyperinsulinemia, or insulin resistance based on when it occurs)—a relatively new recommendation in equine veterinary medicine.
“An endocrine/metabolic evaluation should be part of semiannual wellness programs and is recommended throughout the life of the horse,” he says. “Even a weanling can develop obesity through overfeeding. This is noteworthy because the length of time that a horse is obese is likely to be important in developing equine metabolic syndrome (EMS).”
The Big Two: EMS and PPID
The primary metabolic conditions of concern are EMS and pituitary pars intermedia dysfunction, also called equine Cushing’s disease or PPID. While EMS can occur in horses of any age, PPID is a degenerative endocrine disease associated with aging.
“Equine metabolic syndrome is significant because it is a collection of endocrine and metabolic abnormalities associated with the development of laminitis in horses, ponies, and donkeys,” Frank says. “Recognition of EMS should prompt management changes that address these abnormalities and lower the risk of laminitis, preferably before laminitis first develops.”
Despite its link to aging, Frank points out that Cushing’s is not just a senior-horse disease: “PPID is showing up in horses as young as 10 years of age. PPID is subtle in its earliest stages and manifests as a shift in metabolism from easy keeper to hard keeper, loss of muscle mass, decreased energy, and poor performance.”
Other signs of PPID development include subtle hair coat changes, such as dullness, thickening, longer hairs in the armpit and other regions, regional patchiness, and unusually long winter hair retention. Frank suggests likelihood of developing disease increases with age, though there is no typical age of onset, and owners should scrutizine horses older than 15 closely.
The hoof disease laminitis is a potential consequence of PPID, as well. “But,” says Frank, “PPID has many other adverse health effects outside of laminitis, including immunosuppression, muscle loss, poor performance, infertility, polyuria and polydipsia (excessive urination and drinking), and hypertrichosis (the abnormal hair growth described).”
Horses with concurrent PPID and EMS (EMS appears to predispose a horse to PPID) are at an even higher risk of developing laminitis than those suffering from either one or the other, because PPID exacerbates hyperinsulinemia (excessive levels of insulin circulating in the blood), Frank adds. On the other hand, PPID also develops in horses with normal insulin regulation and no evidence of EMS; these individuals have a lower risk of suffering from laminitis.
On the whole, the goal of a wellness approach to metabolic disease is to identify at-risk horses before endocrine changes associated with EMS and/or PPID lead to laminitis and other adverse health effects and, then, make diet changes accordingly.
What's in a Metabolic Assessment
A metabolic wellness exam takes into account the horse’s body condition score, with 5 being optimal on a 1-9 scale. The objective is to prevent horses from burgeoning into obese body condition scores of 7, 8, or 9. “Body condition scoring is important rather than looking only at body shape primarily because breeds’ (body types) differ,” Frank says.
Your veterinarian can determine if your horse has regional subcutaneous fat deposits by feeling for fat across his ribs, withers, and buttocks and looking for adipose (fatty tissue) expansion into the prepuce or mammary region. He or she should also score the neck crest (from 0 to 5), as it is a significant indicator of developing obesity (see illustration), and assess the horse’s muscle mass, particularly along the topline, because muscle wasting could be a sign of metabolic diseases such as PPID.
Your veterinarian will examine the horse’s locomotion, hooves, and digital pulses for signs of hoof pain indicative of laminitis. “Divergent growth rings or expansion of the white line are indicators of subclinical laminitis (which isn’t severe enough to present readily observable signs),” Frank says. “More overt laminitic concerns are expressed by lameness when circled or walked on hard surfaces.”
And don’t forget the importance of the horse’s hair coat as a possible PPID predictor. Some PPID-afflicted horses’ sweat is patchy and otherwise abnormal as well.
“Other associated conditions result from immunosuppression due to PPID: Sole abscesses, white line disease, sinus infections, tooth abscesses, and intestinal parasitism are just a few,” Frank continues.
He advises that it might be best to delay a spring wellness examination until the horse’s normal shed-out period, particularly if you suspect your horse has PPID. “This allows the veterinarian to ask questions and examine the hair coat,” he says. “The fall examination can be done anytime, but late summer is better for horses already diagnosed with PPID so that the pergolide dosage used to treat it can be adjusted ahead of the autumnal seasonal increase in hormones.”
Wellness from the Start
Building a healthy foundation is important for any horse, and it starts early in life. “A young horse that is allowed to become obese is more likely to develop hyperinsulinemia (excessive levels of insulin circulating in the blood), the component of equine metabolic syndrome most closely linked with laminitis,” says Nick Frank, DVM, PhD, Dipl. ACVIM, professor of large animal internal medicine and chair of the department of clinical sciences at Tufts University’s Cummings School of Veterinary Medicine. “I have had to manage cases of laminitis caused by endocrine abnormalities in horses as young as 2 years of age. This is important because persistent hyperinsulinemia might also impact joint health and development of growth plates.”
In other words, the same high-energy diets that lead to obesity can also cause physitis and other manifestations of developmental orthopedic disease (DOD).
Nancy S. Loving, DVM
In addition to a diligent physical evaluation, there are specific diagnostic tests veterinarians can perform to obtain more precise information about insulin dysregulation in horses with clinical evidence of endocrine/metabolic disorders.
“During the wellness examination, the first question is whether any of the history (weight gain or loss, performance changes, shedding, excess urination and/or drinking) or physical exam findings raise suspicion,” Frank says. “If yes, then it is appropriate to do further diagnostic testing. If no, then blood tests are optional.” In the former case he recommends:
For a horse with the EMS phenotype (physical appearance and genetic propensities), the most sensitive field test for diagnoseinginsulin dysregulation is the oral sugar test (OST). An excessive insulin response to orally administered sugars is the first indication of insulin dysregulation, and later insulin resistance exacerbates it. If an owner is nervous about administering sugar, then the veterinarian can check the horse’s fasting insulin concentration first to ensure he is not profoundly hyperinsulinemic before performing the OST. As long as the fasting insulin concentration is normal or only moderately elevated, he says the practitioner should perform the OST to fully assess the horse and then make dietary recommendations.
- For a horse with suspected early PPID, Frank recommends the thyrotropin-releasing hormone (TRH) stimulation test because it is the most sensitive test available for confirming hormone observations indicative of this disorder. If the veterinarian suspects moderate or advanced PPID, determining the horse’s resting adrenocorticotropin hormone (ACTH) concentration is sufficient.
“To be proactive about detecting a problem in a horse without signs,” says Frank, “an oral sugar test can be performed to detect insulin dysregulation or a screening panel can be obtained once a year in the fall when hormones are most stimulated to check for hyperinsulinemia and PPID. Blood (for the screening panel) is collected after a short fast—the horse is left with only one flake of hay at 10 p.m. the night before and not fed again until after blood is collected the next morning.”
Some universities offer a complete panel that measures glucose, insulin, triglycerides, leptin, and ACTH. When evaluating ACTH results, the lab should use a season-specific reference range.
“The length of time that a horse is obese is likely to be important in developing equine metabolic syndrome.”
Dr. Nicholas Frank
Dialing in the Diet
In addition to the insulin dysregulation described, Frank notes that obesity has negative health consequences ranging from abdominal lipoma (fatty tumors) formation to additional stress on joints and bones.
A horse suffering from insulin dysregulation experiences these elevated insulin concentrations due to dietary sugar and amino acid intake. “In light of that,” says Frank, “The diet must be adjusted to prevent this exacerbation. If obesity is present, caloric restriction is required.
“In old horses (with or without PPID), senior diets are recommended if the horse is losing condition. Higher calorie diets might also be required for horses with PPID that have lost muscle mass.”
The main principle to keep in mind when managing these horses, he says, is to feed adequately without promoting obesity and to address each individual’s specific needs. “Other decisions about feed amounts, sugar content, and pasture access depend upon BCS findings and OST results,” he adds. “Diets high in sugars to accelerate growth are not recommended in young horses. If the nutrient content of the diet is low, a ration balancer should be used to provide additional minerals, vitamins, and protein. Supplemental vitamin E (1,000 IU/day) is also recommended because PPID is thought to develop as a result of oxidative damage,”—and vitamin E possesses antioxidant properties.
Besides careful diet control, Frank always recommends exercise to help prevent obesity.
Other Preventive Care Efforts
Immune system aging is an expected phenomenon in older horses, but in PPID horses the immune system is already suppressed. With that in mind, Frank suggests owners consider vaccinating affected horses three times a year, rather than the typical two, if recommended by their veterinarian. He also advises checking fecal egg counts at least once or twice a year: “PPID-associated immunosuppression leads to higher parasite loads, including roundworms (Parascaris equorum) that are usually uncommon in adult horses.”
Metabolic wellness is a key component to a horse being able to perform at his best and live a comfortable and long life. “The most important advice is for owners to be vigilant about metabolic problems developing and to engage in a discussion with their veterinarian,” Frank says.
Scheduling a twice-yearly veterinary wellness exam can help you and your veterinarian detect metabolic problems and intervene, preventing future damage. If you suspect your horse has an endocrine or metabolic disorder, your veterinarian can perform tests to reach an accurate diagnosis and devise a management plan. The consequences of metabolic conditions can include life-threatening and painful laminitis, so the objective is to proactively avert them. “There are no benefits to obesity,” Frank concludes.
About the Author
Nancy S. Loving, DVM, owns Loving Equine Clinic in Boulder, Colorado, and has a special interest in managing the care of sport horses. Her book, All Horse Systems Go, is a comprehensive veterinary care and conditioning resource in full color that covers all facets of horse care. She has also authored the books Go the Distance as a resource for endurance horse owners, Conformation and Performance, and First Aid for Horse and Rider in addition to many veterinary articles for both horse owner and professional audiences.
POLL: Visits from the Vet