Obesity in Horses: II, Balancing Diet and Exercise

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Written By Dr. Kris Hiney

In Part I of this series, we talked not only about the difficulty in removing extra pounds from our equine companions, but also the health benefits that our horse will gain from doing so. Our strategies included seeking a more mature grass hay with a lower caloric density and reducing the amount of forage offered to the horse.   The horse will probably need to be confined to a dry lot, but fed in a way to minimize boredom related to reduced  feeding time. This month’s article will look more closely at the diet of our horse, to ensure that we are reducing the calories the horse receives, but are still feeding a balanced diet that provides sufficient amounts of our other nutrients.
We will continue to use the example of our 1300 lb horse who was at a body condition score of 8 and a goal weight of 1165 lbs. The maintenance requirement for the 1165 lb horse was 17.7 Mcal per day. We decided to feed the horse at a rate of 1.5% of its target weight in order to achieve the desired weight loss. That would mean our horse would consume 17.5 lbs of feed per day. Now, because we specifically chose a lower calorie hay which is more mature, it probably is lower in other nutrients as well. In order to ensure that your horse’s amino acids, vitamin and mineral needs are met, one should look for a low calorie supplement. Fortunately many reputable feed companies produce feeds that are designed for the easy keeper. Typically these feeds will be much higher in crude protein, minerals and vitamins and are designed so that you only need to feed one to two pounds per day. This ensures that your horse will not suffer from deficiencies while we achieve the desired weight loss.
Additionally, we can accelerate the horse’s weight loss by instituting a regular exercise program. Now, assuming our horse was at a body condition score of 8, it probably wasn’t on a consistent exercise program earlier. The key in implementing an appropriate exercise program is to realize that the horse is relatively unfit and we should begin exercise carefully. Ideally the horse should be ridden or worked five to six days per week.   If this is not possible, try to institute an exercise program at least every other day. Begin with intermittent periods of walking and trotting, and slowly increase the duration of the trotting periods. You should notice that the horse is able to recover its heart rate and respiration rate more quickly during the walking recovery periods as it becomes more fit. Then you can increase the intensity of its exercise program.
Now let’s take a look at how much exercise your horse needs for increased energy expenditure. For every 45 minutes the horse spends walking per day, it will expend an additional one Mcal/d of net energy.  But what exactly is net energy? To this point in time, we have always discussed the energy needs of the horse in terms of dietary energy or DE. Dietary energy refers to the energy available in the feed once the digestibility of the feed is taken into account. When we determine how much to feed our horse, it is always based on the DE concentration of the diet compared to the horse’s DE requirements. Net energy is more specific about the flow of energy through the horse’s body. Net energy refers to the amount of energy needed to support exercise, growth, lactation, etc. after other energy losses to the horse have been accounted for. These other energy losses include the energy lost from gas production, urine, the work of digestion and the heat lost from the digestion and fermentation of the feed. The energy that is left over after all of these losses is what is available for the animal to use for other purposes.
The efficiency of conversion of dietary energy to net energy of a horse in light-to-moderate exercise is only about 40%. Therefore, if the horse expends 1 Mcal of net energy, he actually used 2.5 Mcal of DE.  Even regular trail riding will greatly help the horse with our weight loss goals, but increasing the exercise intensity will increase the calorie expenditure even more. If we use the horse’s heart rate as a guide, we can determine how much exercise they need to perform to represent significant calorie expenditure. Let’s say we would like to increase our horse’s energy expenditure to 20% over his maintenance energy requirements. Our goal for our original horse, then, is to use an additional 3.5 Mcal every day.   Our horse’s typical heart rate when he is walking is usually around 60 bpm while trotting will elevate the horse’s heart rate to around 90 bpm. This relates to 24 kcal/min and 56 kcal/min of net energy respectively for walking and trotting.    If we convert that to Mcal of DE, our horse is consuming .06 Mcal /min or .14 Mcal of DE/min. To achieve an energy expenditure of 3.5 Mcal, that would mean we would walk our horse for almost an hour a day, or about a half hour of trotting.  However, these are heart rates of horses which already are fit. For the obese horses we are discussing, the heart rates are usually higher, thus less time will need to be devoted initially to exercising these guys. Good news for them! Heart rates for an unfit horse trotting have been recorded at 120 to 140 bpm! This would correspond to about 0.25 Mcal of DE per minute. Thus only about 15 minutes per day would achieve our increase in energy expenditure of 20%. Remember, this would be 15 minutes total of trotting with intervals of walking. As the horse begins to become more fit and its heart rate lowers, he will tolerate more exercise and will need to increase the amount of time he works to continue using the same amount of calories.
Alternatively, once our horse is fit, we can also add bouts of cantering or loping to his exercise program.   A horse which is cantering typically has a heart rate between 110 and 130 beats per minute and utilizes about .25 Mcal of DE/min. If we add 10-20 minutes of cantering to our exercise program, the duration the horse needs to be ridden to achieve our target energy expenditure would be about 45 minutes per day, which is probably more realistic for most horse owners. This would include a mix of walking, trotting and loping. Combining this regular exercise program with our restricted diet will help your horse add years to his life.
Good luck with your weight loss goals.

Obesity in Horses

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Written By Dr. Kris Hiney

Just like in people, many horses suffer from obesity related health issues. Overweight horses can have more trouble with joint issues, suffer from exercise intolerance and can even develop metabolic problems. While many horse owners know the risks of having an overweight horse, it may be difficult to reduce weight in these horses – certainly the horse is usually an unwilling participant!  In this article we will address management techniques and dietary strategies designed to reduce weight, but still keep the horse physically and mentally healthy.
First of all, which horses are good candidates for losing weight? Ideally most performance horses should have a body condition score around five. Horses that are slightly overweight, or have a body condition score of 6 or 7, shouldn’t be at a great risk for health issues, but certainly will perform better at a condition score of 5 or 5 1/2. Horses above a 7 have more risk of developing health issues such as insulin resistance, metabolic syndrome, or even Cushings in their later years. If the horse with a high body condition score also has uneven fat distribution, he is more likely to have metabolic issues, and may even be harder to remove weight from than a horse with a more even fat distribution (personal observation). Horses that have cresty necks, substantial amounts of fat over the tailhead, enlarged abdomens and fat in the area of their mammary glands or sheath fit this category.   It is more critical for these individuals to lose weight. Now that we have identified the horses which need to lose weight, let’s address a healthy weight loss plan.
One of the first issues to address is the quality of the horse’s forage. Ideally we will feed dieting horses harvested forage/hay, rather than pasture as it is easier to monitor their intake. Horses that are overweight will do better on mature grass hay which has less caloric density than alfalfa or alfalfa-grass mix. When selecting hay, look for more mature hays that have been cut at a later stage of growth. Typically these will be coarser stems and have seed heads present in the hay. However, when looking for lower energy hays, don’t sacrifice the overall quality of the hay – it should not contain weeds, debris, dust, mold, etc. We are just looking for fewer calories, not hay that your horse shouldn’t eat! Once we have the correct hay type, the owner will have to limit their horse’s intake. This can often be confusing, as we typically teach owners to feed based on a percentage of the horse’s body weight. However, in this case, we have a horse that weighs too much, and is consuming more hay/forage than it should. Let’s take a look at the math involved to determine how much the horse should eat.
For an example, we will start with a 1300 lb horse who has a body condition score of 8. If we looked up this horse’s energy requirements for maintenance, it would need 19.7 Mcals per day. But that energy requirement is based on a horse that is in a lean body condition. Remember that it takes more calories to maintain metabolically active tissue like muscle than it does fat.   So even if we fed our horse at its maintenance requirement, it is still receiving too much energy for its body type. We will now assume that for every body condition score we want the horse to lose, it should lose about 45 lbs. For our 1300 lb horse, our target weight is actually closer to 1165 lbs [1300 lbs-(45lbs x 3 body condition units)]. The maintenance requirement for the lean 1165 lb horse is 17.7 Mcal per day.    Using these numbers, we will calculate out how much hay this horse would need to provide that amount of energy. For this example, I will use a grass hay of advanced maturity with a caloric density of .86 Mcal/lb as fed. The amount of hay the horse would consume using our 19.7 Mcal figure would be 23 lbs of hay (19.7 Mcal/0.86 Mcal/lb), while the horse would receive 20.6 lbs of hay if we intend to provide 17.7 Mcal (17.7 Mcal/ 0.86 Mcal/lb). Let’s compare that with the standard feeding guidelines for horses based on body weight. If the target weight of our horse is 1165 lbs, and we fed at 2% of the target body weight, our horse would receive 23 lbs of hay. That certainly wouldn’t work because that would provide enough calories to maintain his current weight of 1300 lbs! So how much do we need to reduce his hay intake? If we feed the horse at 1.75% of its target body weight, the horse would receive 20.4 lbs of hay per day. However, even feeding at this rate will probably not get us to their target weight. Therefore, in order to really achieve weight loss in our horse, we should probably feed closer to 1.5 % of the horse’s target weight. That means our horse would only be eating 17.5 lbs of hay per day. For the horse owner, this means that in order to successfully achieve weight loss, we need to get a scale out to the barn, and physically weigh out the amount of hay the horse will consume in one day. While this may be time consuming, it is the most accurate technique to deliver the correct and consistent amount of calories.
Now let’s talk about some other practical issues. A horse that is only consuming 1.5% of its target body weight is going to have some “free time” that it is not used to having. We need to provide mental stimulation for this horse or it may development unwanted stereotypies such as cribbing or wood chewing. Continual stalling would not be ideal as this will certainly lead to a great deal of boredom and frustration. If possible, the horse should be kept in a dry lot (free access to pasture certainly won’t help!) with secure fencing. Do not underestimate the horse’s ability to get through the fence to graze! Also, providing other horses with which to interact, stable toys, etc. will help relieve boredom. If you find your horse finishing his meals too quickly, putting the hay in a hay net which is tightly woven may also slow down his rate of intake and alleviate boredom. While these strategies may sound tedious, it is important in order to improve the overall health of your horse.
Next month we will continue to discuss the dietary needs of a horse in a weight loss program, as well as how to safely use an exercise program to encourage weight loss.

Preparing for the Breeding Season

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Written By Dr. Kris Hiney
While breeding season may be the last thing on anyone’s mind at this time of year, it will be coming soon. Now is the time to ensure that your mare or stallion is going to be at their optimal reproductive efficiency. While much of a mare’s or stallion’s fertility depends on other factors such as age, condition of reproductive organs, etc., there are some basic management steps we can take to ensure that as few cycles of inseminations are needed to get a mare pregnant. Multiple breeding attempts can quickly outstrip the original stallion breeding fee and be a significant cost to the mare owner. Often we forget that every shipment of semen may be an additional cost, followed by extra veterinary fees, mare board, etc. Therefore it is in the mare owner’s best interest to have her in optimal condition before the first breeding attempt ever occurs.
So how do you prepare your mare and stallion in January to begin breeding anywhere from February to mid-summer? The easiest place to begin is to look at your horse’s body condition score. For a mare, we want her to be at a body condition score of at least 5 or 6 (see “Too Fat, Too Thin, or Just Right”). A mare in this condition would be a moderately fleshy mare whose ribs are covered by fat, has evidence of fat deposition behind her shoulder and over her tailhead, and whose back is level. Mares that are a higher condition score than that may still have no problem getting pregnant, but are unnecessarily obese. This may result in more wear and tear on her joints. Additionally, as there is no increase in reproductive efficiency, maintaining a mare in too high of condition may just be a waste of feed costs. Furthermore, if she has chronically been obese with localized fat deposition, she may even be at risk for metabolic syndrome or insulin resistance (see Equine Carbohydrate Disorders, Part 3: Metabolic Syndrome).  If your mare is diagnosed with metabolic syndrome, it is important to correct her metabolic profile and manage her carefully through the breeding season. Altered hormonal profile can impair her ability to become pregnant and certainly extra weight in a laminitic mare may increase her level of pain.
If we look at the opposite condition and the mare is too thin, she will need more cycles to settle compared to a mare at adequate condition. She also may take longer to return to normal cyclic activity following winter anestrous (when mares cease to cycle due to the shorter day length). Thin mares’ conception rates may be lower, and if she foals in a thin condition, she may take longer to begin cycling again. With so many negative effects of trying to breed a thin mare, one of the easiest ways to increase reproductive efficiency is to put weight on your mare!
Stallions also use more energy in the breeding season due to the increase in their activity levels. Stallions which breed mares in an intensive live cover breeding system will of course need more energy than a stallion which is bred only once every other day. Stallions which are more extensively used would have energy requirements similar to a light to moderately exercising horse, and their maintenance requirements will also be elevated (see “Energy for Work”).  Typically, stallions are simply more active during the breeding season as they exhibit their normal sexual behavior. Ideally, stallions should be maintained in a body condition score close to 5 throughout the breeding season.
Beyond just meeting a stallion’s energy requirements, feeding of Omega-3 fatty acids may help improve his reproductive efficiency. In a study by Harris, et al, published in 2005 in Animal Reproduction Science, stallions supplemented with dietary Omega-3 fatty acids increased their daily sperm output.  Furthermore, there was an increase in morphologically normal sperm in the supplemented group.  The greatest response was seen in the stallion with initially the most morphologically abnormal sperm. In this study, one stallion who was considered to be a “poor cooler” improved his post cooling progressive motility from 23 to 38% in a 48 hour test cool. Therefore, supplementation of Omega-3 fatty acids may be a valuable tool in improving the reproductive characteristics of sub-fertile stallions.
Basic guidelines for increasing body weight and condition in horses are really no different for the broodmare or stallion than in other classes of horses. The quicker the gain is needed in the horse, the larger the increase in calories which must be offered daily. If you only have two months to get your mare in condition, you need to increase her energy intake by 30-40% to increase her body condition score by one number. If we have three months, which may be more realistic, the energy requirements increase by 20-30%. Remember, however, if you are trying to accomplish weight gain during the winter, she may also have an increase in energy requirements due to her need to thermoregulate. This will make weight gain more difficult. To add calories quickly to the diet, look for a fat-added feed that will be digested quickly and efficiently.  Remember that fat offers 2.25 x the calories that will be in grains which consist primarily of simple carbohydrates. Fat will also disrupt the metabolic profile of the horse to a lesser extent than a diet high in sugars and starches.
Of course, beyond caloric intake, always ensure that your breeding horses are consuming a complete balanced diet in respect to all nutrients, have good health care and are suitable candidates for breeding. Breeding horses is a big responsibility in terms of the care and well-being of the mare, stallion and the subsequent offspring.