This is the sixth article in the "Fix It With Feed " series. Check back every Wednesday for more articles on nutrition and how it affects performance.
When it comes to equine nutrition, we often stress about whether our horses are carrying enough flesh. However, the well-padded look that might be perfect for the show ring is often too heavy for excellent health.
“Horse people have different standards of what is ideal; most horses are too pudgy,” said Martin Furr, DVM, Ph.D., Diplomate ACVIM and Adelaide C. Riggs Chair in Equine Medicine at the Marion duPont Equine Medical Center in Leesburg, Va. “You want your horse to be a 5 on the body condition score scale [out of 9]. That’s optimal.”
Having a horse that’s too fat can lead to all sorts of metabolic issues, including Equine Metabolic Syndrome and insulin resistance.
The poster horse for EMS is one that is obese, laminitis-prone and also insulin resistant.
“Insulin resistance is just a condition in which the body does not respond appropriately to the insulin that is present,” said Furr. “The body is producing insulin, but the cells are not responding to the insulin that’s there. There’s a range. You could have a tiny bit of reduction of response to a huge amount of response.”
No one knows exactly why some horses become insulin resistant, but factors such as obesity, lack of exercise and long-term intake of feeds high in glucose seem to be part of the equation. Horses are typically between the ages of 8 and 18 when insulin issues begin, and some breeds—Morgans, Arabians, Paso Finos, some warmbloods and ponies—tend to become overweight more readily than other horses, thus they are more often insulin resistant.
Diagnosing The Problem
“Horses that are insulin resistant tend to have some similar physical characteristics,” said Olivia Martin of Performance Feeding. “General obesity with areas of patchy fat accumulation, usually over the crest of the neck, over the shoulders, and fatty deposits over the croup and on either side of the tail head. Geldings can have fat deposits surrounding the sheath, and broodmares can have fat surrounding the udder. Horses that are insulin resistant are usually defined as easy keepers, and are often fat even though they are fed calorie-restricted diets.”
Insulin resistance can be diagnosed by a simple blood test, where the blood concentrations of insulin, ACTH (thyroid hormone) and other major hormones are recorded. A glucose tolerance test can also be performed. This test requires giving a horse a known quantity of glucose, then taking sequential blood tests to monitor the horse’s insulin response.
One of the major complications of EMS and IR is the development of laminitis.
“The insulin will be too high because the cells are not responding to the insulin that’s there, so it’ll crank out more,” said Furr. “Nobody really knows for sure what high levels of insulin do in the body. It appears that it’s damaging to the lining of blood vessels, especially in the feet. It appears there’s toxicity to those tissues. It’s also probably doing something metabolically to the cells that we don’t understand yet. It also causes inflammation, which is also damaging to the feet.”
While there are some supplements on the market to help manage EMS and IR, Furr and Martin don’t believe they are very helpful.
“There’s probably a gazillion supplements and herbal things that people are trying to sell, but we just don’t know if they’re useful or not. The key things is decrease their food, increase their work,” said Furr.
Step 1: Kill The Carbs
The first problem with overweight horses is providing the appropriate amount of calories without overloading them with starch and sugars. Cutting out sweet feed, molasses and whole grain such as corn and oats is the first step in equine weight loss.
“Often these horses cannot eat grain meals, and un-molassed beet pulp can be used as a carrier for any medications or supplements,” said Martin. “Un-molassed beet pulp can be used as a substitute for a up to 1/3 of the hay fed per day: For example, if a horse should be eating 15 lbs of hay per day, feed 10 lbs of hay per day and 2½ - 4 pounds of un-molassed beet pulp per day.”
If giving your horse a concentrate ration is absolutely necessary, then there are several low-carbohydrate feeds on the market. You want to look for a feed that has a low carbohydrate but high fat content.
“We want to get rid of as much sugar as possible. You can still overfeed, so you still have to feed an appropriate volume. Metabolic diets are typically low sugar and higher fat than the typical sweet feed,” said Furr.
Step 2: Forage And Pasture Management
Since most horses will do exceptionally well on a diet comprised mostly of forage, it’s important to feed a good quality hay, as well as maintaining your fields. However, for EMS and IR horses, pasture management quickly come into play.
“You may have to restrict their access to pasture,” said Furr. “A horse can eat roughly half of his daily requirement in three to four hours. You want the turnout to be at night, because the amount of sugar in the grass is lowest at about 4 a.m. The highest content is about 4 p.m. Definitely keep them off the spring grass.”
In addition to considering a grazing muzzle, you can also turn out in a dry lot. However, Furr cautioned against turning out in a field with stubble or patchy grass, as low quality pasture tends to have fructane in it, which contributes to laminitis.
“In addition, test your hay if possible to determine the carbohydrate level,” said Martin. “If this is not possible, soaking the hay (fully submerging soak for 30 minutes in hot water or 60 minutes in cold water) can reduce the available carbohydrate in the hay by as much as 30 percent.”
Step 3: Exercise
Once you have your feeding program up to snuff, exercise is the final and most important part of putting your horse back on the right track, health wise. Getting your horse into an exercise routine that is appropriate for his age and ability will dramatically improve his way of life and obesity issues.
“When you pull their weight down and get them exercising, lots of times the IR goes away,” said Furr. “Decrease calories that go in, increase the calories they’re burning. Most of the time they don’t need the extra calories unless they’re working hard. Horses that are working hard generally don’t have this problem.”
Other Metabolic Problems
Cushings is another major metabolic problem that owners of older horses often face. Cushings disease is a disorder of the endocrine system in which the pituitary gland is enlarged, and it excretes excessive amounts of hormones, some of those being the cortisol-based hormones. Cushings horses tend to combine weight loss with a big belly. The cortisol causes muscle weakness, long shaggy coat, association with laminitis and poor resistance to infection.
In general, Cushings is managed with various forms of medication, but keeping an affected horse on a strict diet plan is also helpful to his health and soundness.
“Each horse is individual, but in general, those guys can be given medication to shrink the pituitary gland,” said Furr. “Those horses tend to require some management help. You have to pay attention to their feet, clip them in the summer. If they’re thin, they’ll require a feeding program that increases the amount of energy they get, but you don’t want to give them too much carbohydrate and soluble sugar, because that will worsen their insulin resistance and put them at an increased risk for laminitis. You want to give them more total calories but less from carbohydrates.”
“If a horse has been diagnosed with Cushings, feeding it like a horse that is insulin resistant will not be harmful and can be preventative of future metabolic conditions,” said Martin.
However, horses with Cushings do not always have insulin resistance, so it’s important to consult with your veterinarian and a nutritionist before throwing your horse on a new diet.
Read Part 1: You Don't Need A Ph.D. To Puzzle Out Protein
Read Part 2: Feeding A Hard Keeper Is All About Extra Calories And Patience
Read Part 3: Alfalfa Is More Helpful Friend Than Foe 
Read Part 4: Prevent Ulcers By Mimicking Nature
Read Part 5: Dealing With Allergies Can Be A Tricky Business