How to determine the ideal weight for your horse for health and soundness.
By: Shannon Pratt-Phillips |
Achieving and maintaining a healthy body condition score and body weight can be one of the most important things you do for your horse in his life. Adiposity, or carrying too much body weight, can negatively affect things such as joint soundness, exercise tolerance, reproduction and inflammatory status, and it predisposes your horse to laminitis. Luckily, maintaining an ideal body condition score is a relatively straightforward process, but it can require a good deal of work and dedication from you, the owner.
So, how do you know if your horse is in good weight? Body weight, or body mass, is simply a number on a scale, and is affected greatly by the horse’s height and build. But, when horses are overweight, those numbers will increase. Many horse owners don’t have access to an equine scale, and, therefore, rely on estimates.
Body Condition Scoring
Much of a horse’s body fat is subcutaneous – or just under their skin, so it can be easily felt and covers the horse’s body frame. To determine how much fat a horse has, a veterinarian can perform an ultrasound on several areas of the horse’s body and look at the thickness of the layer of fat between the skin and underlying muscle.
Body fatness can also be estimated more easily using the body condition score (BCS) system that was developed by Dr. Henneke. This is a 1-9 scale, where a 1 would represent a severely emaciated horse and a 9 would represent a grossly obese horse with bulging fat. By running your hands over the horse’s body, you can feel how much fat is below the skin, and assign a score to areas of the horse’s body (see Body Condition Scoring Chart on page 33). One should remember that body condition scores are highly subjective, and might differ slightly between people, so you should try to have the same person score your horse each time. Monitoring BCS every two weeks to once a month is recommended.
Ideally, most horses should be a body condition score of 5 – where they have some fat coverage, but not too much. Many horses are healthy in the 4-6 range, but based on work in other species (particularly dogs, where if you keep them on the thin/ribby side they live longer and are healthier overall), leaning towards the 4-5 range may be better. Seeing some ribs is not of concern, and, in fact, a horse that is a 4 (and otherwise in good condition, including sufficient diet, good coat quality, etc.), is FAR healthier than a horse that is a 7, 8 or 9.
There may be some cases where a more conditioned horse is desirable (for cosmetic reasons, such as for halter classes), but this is not ideal from a health standpoint. Broodmares should be kept in a slightly higher condition (6-7), but this is based on reproductive efficiency and the ability to support a fetus and have sufficient milk production. Many performance horses do well on the leaner side (particularly racehorses), but they should have sufficient fat stores on their body to support their energy needs for sport. Research has shown that endurance horses with higher (but still less than 5) body condition have a higher likelihood of finishing a race than those with lower scores (BCS <3). Many sport horses are kept a little higher than a 5-6, which may be partly cosmetic, but may, in fact, be a detriment to performance if they are carrying excessive weight. Some older horses do better if they carry a little extra weight (BCS of 6) because regaining and maintaining weight can be tricky sometimes in seniors and that higher goal gives you some cushion. However, issues with arthritis, mild lameness or previous laminitis may prescribe carrying less body weight (BCS of 4-5).
Because body condition scoring is subjective, some research has looked at other means of assessment that are more objective. Measuring the belly circumference (around the abdomen at the point of the umbilicus) can detect more sensitive changes in adiposity/weight than body condition scoring or weight estimates. The heart girth to height ratio has also been used to quantify obesity in horses, where a ratio greater than 1.26 suggests a horse is overweight (1.33 for ponies) and a ratio greater than 1.29 suggests a horse is obese (1.38 for ponies). Using a combination of methods and good record keeping can help you monitor your horse’s body condition.
Body Weight Measurement
The best estimate for body weight in horses uses the heart girth circumference (from behind the elbow, up around to the withers, just beyond the highest part where the mane hairs become sparse) and the horse’s body length (from the point of the shoulder, up on an angle to the point of the buttock). When measurements are recorded in centimeters, using a soft measuring tape, to determine the weight in kilograms, the formula is: heart girth x heart girth x body length/11,990.
Calories and Fat
To achieve the ideal body condition score (and weight) it all boils down to what that subcutaneous fat is – stored energy. Calories. Ideally, the amount of calories coming into the horse as food is equal to the calories expended by the horse in basic metabolism, breathing and heart pumping, temperature regulation, work or exercise, and any other physiologically demanding processes (such as growth, lactation or pregnancy). If a mature horse consumes too many calories, he will store those calories as fat and gain weight and condition, and if he doesn’t consume enough, he will use the stored calories in his fat reserves and lose weight and condition.
We can get estimates for how many calories a horse needs from the research summarized in the National Research Council’s Nutrient Requirements of Horses (2007). The basic formula for energy requirements of a mature horse at maintenance (not in work) is 33.3 kcal/kg body weight (where 1 kcal = 1 Calorie), and thus a 500kg horse would require 16.7 mcal/day (where 1 mcal or megacalorie is = 1,000 kcal).
However, we know that not all horses are created equal, and some horses have faster or slower metabolisms. Thus, the NRC uses a value of 30.3 kcal/kg for easier keeper, slower metabolism types of horses, and 36.3 kcal/kg for hard keeping, higher metabolism types of horses. In the real world, these actual values may still be higher or lower among different horses.
How can we figure out how many calories our own horse needs? We could just get estimates of the energy content of all of the feeds your horse is given and add all of those up to get a total calorie intake per day. But, in practicality, do we need to do this? Probably not – as the EASIEST way to tell if your horse is getting the calories he needs is to just look at his body condition score. Again, if he is overweight, or gaining weight, the calorie intake of his diet is too high, and vice versa.
We KNOW hay (or pasture) is the most important part of a horse’s diet, and so this should always be the basis for any equine diet. When hay is offered free choice, many horses will consume between 1.75-2.25% of their body weight. Horses do tend to consume more pasture if available, with records of some ponies consuming more than 5% of their body weight! This is why overweight horses should not be kept at pasture. If body weight and condition can be met with the calories coming from hay (or pasture) alone, then great, no concentrated energy sources are needed. Mind you, the horse will likely need a vitamin and mineral supplement, and perhaps also a protein supplement if the hay is low in protein.
If the horse needs more calories (due to extra work, growth, lactation, etc.) then concentrates can be offered. Cereal grains are great sources of energy, but may be low in protein, some minerals and vitamins, so if the diet consists of hay plus a cereal grain (like oats, corn or barley), you will still need to supplement vitamins and minerals. If you choose to feed a commercial feed, these will have been fortified with vitamins and minerals and additional supplements of these are not needed. You might also consider adding some fat (eg. vegetable oil) to increase the calorie density of the diet.
For a horse that needs to gain weight, the first step is to increase the amount of hay that he is offered – if he is not offered free choice hay. I like to also offer soaked hay cubes, beet pulp and/or rice bran to increase the fibrous component of the diet to the maximum. Assuming the horse is already on concentrates, mixing some oil in with the grain can greatly increase calorie intake. You can feed up to two cups of oil safely, as long as their poop doesn’t become shiny looking. Increasing concentrates can certainly also increase the calorie density of the diet, but comes at a risk of increasing the chance of colic. If you do decide to increase grain, try to do so by adding another meal to the daily routine, rather than increasing the amount fed at each meal.
Helping a horse lose weight can often be more challenging. However, the premise is still basic math – consuming fewer calories than the horse needs. This can be done by either decreasing the calories in the diet, or by increasing the energy expenditure of the horse through work. Decreasing calories in the horse’s diet can start with eliminating all grain, and restricting pasture the horse gets – by limiting time or using a grazing muzzle; and eliminating it all together in some cases. Pasture is very important to limit, because we cannot control how much they eat when they are on it. Research has shown that if horses are only out for a few hours per day, they INCREASE their intake rate so they can actually eat more in that shorter time frame! Grain is fed for calories, which your horse doesn’t need, so that is an easy removal. Some horses will also need their hay allocation decreased. Horses shouldn’t be fed less than 1% of their body weight in hay, but decreasing it to 1.5 or even 1.25% of body weight is common protocol for overweight horses (and some serious cases will be limited to only 1%). This will require someone weighing the hay out every day. Because this limited amount of hay could be consumed quickly, we often need to find slow feeders for the hay to prolong how long the hay lasts. Finding lower energy density hay can also trim some calories.
Exercise is also a great way to increase calorie expenditure. Ideally, you can increase the duration, intensity and frequency of your horse’s workouts, but if your horse has lameness issues, then hand walking is helpful (daily, for as long as the horse will tolerate). There is one drug (Levothyroxine) that will increase your horse’s metabolism to help him burn more calories daily, and may help facilitate weight loss, but this should be a last resort. Supplements that claim to facilitate weight loss are not scientifically proven and probably not worth the money.
Sticking to It
While the basics of weight maintenance are simple, the hardest part is the owner actually doing it. Owner compliance and dedication (and also barn manager/worker participation) is one of the most important things that will predict how well a horse responds to nutritional changes in effort to help them get to their ideal body weight and condition.
As always, make sure you work with an equine nutritionist to help you formulate a diet that has the calories your horse needs, but also sufficient protein, vitamins and minerals.