In the last article, we tried to categorize exactly how much work your horse is performing, and how many calories he needs to consume to match his energy output with his energy input. If you have been following along our series, you now have determined how much your horse weighs, what his body condition score is (and what it might need to be), and how many calories your working horse needs at rest and during the period you are riding or training him. Again, we are focusing solely on the caloric part of the equation, realizing that work does indeed change the requirements of some other nutrients. However, if we do not meet our horse’s energy needs, no amount of supplementation will make up for the lack (or abundance) of calories!
This month we are going to discuss other factors that might change your horse’s energy requirements regarding work. This will almost wrap up our discussion of energy needs in horses. However, we still need to discuss the broodmares and babies, especially as the next generation is just around the corner! So let’s begin!
By examining the frequency, the duration and the intensity at which your horse works, you were able to put him into one of four categories described by the National Research Council – light, moderate, heavy or very heavy exercise. However, these distinct categories might not fit for every horse and some adjustments might need to be made. When in doubt, always refer back to your horse’s body condition to assess your feeding program.
To realize why your horse might not fit precisely into these categories, sometimes it is useful to understand how these numbers are actually derived. Energy requirements for exercising horses are actually based on determinations of how much oxygen the horse consumes during an exercise bout. Typically these studies are performed on a treadmill while a horse wears a mask over the nose. The amount of oxygen the horse takes in is compared to how much he breathes out. This allows one to calculate the amount of oxygen the horse used by the difference in oxygen concentration of inspired vs expired gases. The amount of oxygen the horse uses relates to the amount of calories he is burning.
Remember the TCA cycle I mentioned last month? This is where the carbohydrates, fats and proteins (sometimes) are “burned” at the cellular level with the assistance of oxygen to produce ATP. Horses, and people too, need energy in the form of ATP for muscle contraction. Thus, the harder and faster the muscles contract (ie speed or effort), the more ATP they need, so the more oxygen the horse needs to breath in. The amount of oxygen used directly relates to the fuels the horse uses to produce that ATP – the carbohydrates, fats, and proteins provided in the diet.
Exercise physiology break!
|In order to accomplish an increase in oxygen delivery to its muscles, horses perform some rather amazing feats. One of the unique characteristics of horses is that they breathe in rhythm with their stride. Pay attention next time you ride to the blowing noise your horse may make while cantering or galloping. Right in time with their feet! Occasionally they will skip a breath in order to take a next bigger breath, but for the vast majority of the time, respiration rate and locomotion are linked. We call this phenomena stride coupling. So how do they get more oxygen if they can’t breathe faster? Well for one, if the horse is going faster, his stride rate increases and therefore increases his respiration rate. But he also breathes deeper as well. Essentially the horse takes a bigger breath – aided by the contraction and expansion of the horse’s ribcage as he runs faster and extends his stride. This makes breathing very efficient for the exercising horse. But that’s not all they do! Horses also have the ability to boost the oxygen carrying capacity of their blood. Red blood cells are responsible for picking up oxygen from the lungs, traveling through the body and delivering that needed oxygen to the working tissues. The more red blood cells present in the blood, the more oxygen that can be delivered. Horses have a unique ability to store their red blood cells in their spleen, waiting for the moment they are needed. When the horse exercises, adrenalin (epinephrine) is released into the blood, which causes the spleen to contract and eject all of these additional oxygen carrying cells into the horses blood stream. Instant (and natural) performance boost! .
So why might these tests on a treadmill not always reflect the calories your horse needs? Well for one, galloping on a treadmill is relatively easier than working over uneven surfaces. The deeper the footing, the more exertion the horse will need to work. Think of running across an arena – it wears you out faster than running on pavement doesn’t it? Also, if your horse is being worked over hills (a great way to condition their cardiovascular system) this will increase its caloric requirement as well. We don’t typically have riders on top of the horses on a treadmill either. The weight of the rider and tack will also increase the energy demand on the horse.
There are other intangibles as well. The effort exerted by the horse also factors into the equation. Take for instance a jumper who routinely jumps his fences by over 5 inches versus the horse who barely skims over the fence. That horse over-jumping is working harder. The same can be said for almost every athletic event. Think about cutting horses, reining horses, barrel horses etc. The more athletic and talented the horse, the harder he tries, or the more effort he puts into each maneuver. Therefore, we may have a horse who spins faster, cuts a cow with more authority or finishes a barrel pattern with tighter turns and a quicker time. All of these factors affect his energy needs. Conversely, that lazy horse might be ridden the same amount of time as others, but may actually be expending far less energy than you think he might!
The gaits the horse performs can also influence its energy requirements. Typically a horse’s heart rate (which reflects its oxygen needs) increases linearly with speed (see Graph: Heart rate (bpm) vs speed). However, horses can travel at the same speed but be at different gaits. For example, think of someone long trotting a horse next to one that is cantering at the same speed. The horse that is long trotting or using an extended gait, is actually working at a higher intensity and using more oxygen than the horse cantering. The same is true for horses working at collected gaits. Thus, if your horse spends time working at both extended and collected gaits it may explain why they need more calories to maintain their weight than if we strictly account for the time they are ridden. For example, if you have watched dressage horses work at extended gaits, or watched an animated park horse travel around the ring, you can appreciate just how much work these guys are doing!
Just as when we determined a horse’s maintenance requirements, climate, body condition and level of fitness will all affect the amount of calories that horse needs to consume. Remember, while feed tags, equations and tables all provide us with numbers to use in determining how much to feed a horse, they are just a starting point. There is no substitute for the horseman’s eye in evaluating the needs of your horse.