Tag Archives: respiration

  • Water Losses in Horses

    Written By Dr. Kris Hiney

    This month we will discuss the most important nutrient in your horse’s diet, but maybe the most overlooked. Because providing our horse with water may seem obvious, many believe water requirements may not warrant discussion. But how much do you really know about how much your horse should be drinking per day?

    The amount of water a horse needs to consume per day is directly related to how much water the horse loses per day. Horses lose water through four ways: their manure, urine, sweat, respiration, and if a broodmare, lactation. All of these variables must be taken into account when determining how much water our horses should be drinking. When we increase these losses due to variations in diet, work or environment, we must allow the horse greater access to water. Sometime that may mean we need to be creative in encouraging the horse to consume more water.

    One of the greatest water losses to a horse is often overlooked, horse manure. While we tend to think of it as a rather solid form that we must continually scoop, pick up or shovel, horse manure is mainly water. This is especially true if the horse is eating primarily roughages. On an all forage diet, horse manure contains as much as 72-85% moisture. In fact, the water lost through their manure may represent almost 60% of a horse’s daily water intake. If we switch the horse to a grain based diet, the manure actually becomes much drier. Now, that does not mean that this may be a great strategy to minimize water losses. Overly dry feces can lead to impactions and colic, which is certainly to be avoided! When a horse consumes forage, it must be digested through fermentation which requires a fairly liquid environment in the hindgut and therefore normal gut health. In part, this is why it is recommended to always provide at least 1% of a horse’s body weight in forage per day. Consumption of forage therefore encourages water intake.

    Variations in diet beyond just forage versus grain, can influence water losses in horses. The total amount of feed the horse eats will alter its water requirements. As consumption of feed increases, the horse must consume more water in order to allow normal digestive processes to occur. While we mentioned already that forage does increase water losses and thus water intake, the type of forage the horse consumes alters its water needs. Obviously fresh pasture grass contains a much higher moisture content compared to dry feed which is typically only 10-15% moisture. Growing grass may contain as much as 80% moisture. When taking into account the total amount of grass a horse can consume, simple grazing may approach a horse’s basic water requirements. Don’t be surprised then if your horse visits the water trough less frequently while he is grazing compared to when you feed hay.

    Urine obviously contributes to water losses in horses, but remember that the volume of urine may reflect the water balance in the horse. Urine actually represents the most variable water loss in the horse, as other losses are more directly tied to diet, metabolic demands and environment. Some horses simply consume more water than others, and as a result will excrete more dilute urine in order to rid the body of excess water. Alternatively, if we fail to adequately meet our horse’s water needs, the kidneys will act to limit water losses and concentrate the urine. Additionally, if the feed contains components that need to be excreted by the kidney, water losses will increase. For example, when horses are fed protein beyond their requirements, the extra amino acids are broken down into components that can be used for fuel. This process involves the removal of the nitrogen found in amino acids. The kidney incorporates the excess nitrogen into urea, which is then excreted through the urine. Excess electrolytes, in particular sodium and potassium, must also be excreted by the diet. If you have a horse that likes to consume his salt at a greater rate, you may notice that his stall may be wetter than horses which do not perform such a practice. If you own an enthusiastic salt eater, you may want to limit his intake to strictly his salt requirements.

    Sweat represents a tremendous variable in water losses for the horse, dependent on temperature and exercise. Remember that horses are most similar to humans in that we both dissipate heat through sweating, compared to other species that may rely primarily on respiratory cooling or panting. As horses must breathe through their nostrils, panting is simply not an option for them. Increasing the environmental temperature can increase evaporative losses between 45 to almost 400% of the horse’s normal water losses. The addition of exercise on top of environmental losses can quickly lead a horse to dehydration and heat stress if water losses are not replenished. For example, cross country horses have been reported to lose as much as 50-75 lbs of water during a competition due to the sustained duration of activity. Respiratory water losses are also directly tied to temperature and work load as these have the greatest influence on respiration rate. Horses increase respiration rate, either to aid in cooling, or due to the increased demand for oxygen delivery to the muscle tissue. However, relative to sweating, respiratory losses are relatively minimal.

    The good news is that horses, through training or adaptation to their environment, do become more efficient at heat dissipation and begin to minimize their water losses. However, full acclimation to increased environmental temperatures may take up to 3 weeks. While it would be nice if weather patterns would gradually increase over time allowing our horses to adapt, we all know that this is simply not reality. Therefore, when the temperature gage rises dramatically, or even sporadically, we must acknowledge that our horses may not easily be able to dissipate heat. This will require more caution on our part when working our horses during this abrupt changes in temperature.

    Lactating mares also have a significant loss of water through the milk. The amount of milk produced can be very variable between mares, with an average of 2 to 3% of their body weight per day. This will increase their water requirements somewhere between 50 and 75% over their normal requirements. If we also remember that lactating mares have a very high energy demand on their bodies, their feed intake increases as well. Remember that as feed intake increases, the horse must increase their water consumption to maintain digesta flow, and to counter the losses of water through the manure.

    So what does all of this mean relative to what we need to offer our horses? My basic recommendation is to always allow the horse access to water beyond what they are willing to drink. In general a horse will consume around 10 gallons of water per day. This is easily accomplished by offering two full buckets twice a day. However, if you find that the bucket is empty when it is time to refill it, consider hanging an additional bucket. Your horse will thank you!

    Next month we will delve more deeply into the current research on strategies to maximize your horses water intake. We all are familiar with the adage that you can lead a horse to water but you can’t make them drink. However, sometimes we really need them to drink! We will also discuss some feeding strategies that may help your horse stay hydrated through the various activities he may encounter such as traveling, endurance exercise, or exercise during hot temperatures. Remember, there is more to know about water than just filling a bucket!

  • Feeding Horses with Respiratory Allergies

    Written By Dr. Kris Hiney

    Similar to people, horses can develop allergies to environmental contaminants that lead to asthma-like symptoms. In the equine world, this syndrome is referred to as recurrent airway obstruction (RAO). It was previously referred to as chronic obstructive pulmonary disease or (COPD) but due to dissimilarities with the syndrome observed in humans, RAO is now the preferred term. When some horses are exposed to dusts and molds, they develop allergies.  Why some horses do and others do not develop allergies is unknown. There is some evidence that this disease may be genetic. Horses born to affected parents are three times more likely to develop RAO than horses born to non-affected parents. Therefore, if you know your horse is predisposed to RAO, it is even more important to identify the symptoms and to properly manage its environment.
    Identifying RAO
    When the horse is exposed to an allergen, the body responds by increasing inflammation through the bronchioles coupled with bronchoconstriction.  The lungs increase in mucus production which the horse may not be able to clear easily. Frequently nasal discharge is seen, along with coughing, an increase in lung sounds and more distress during breathing. Lung sounds are typically heard with expiration, or the horse will “wheeze” when breathing out. Continual exposure to allergens may lead to fibrotic changes within the lungs. This will result in a horse which cannot take in oxygen to the same extent as an unaffected horse. You may notice that the horse has an increase in respiration rate over what is normally experienced during exercise, or he may become more exercise intolerant or fatigue easier. Horses with this syndrome which have had it more severely or more chronically may even develop a “heave line”. This is due to the hypertrophy of the abdominal muscles which must be used to assist the animal in breathing, rather than just solely using their diaphragm.
    Management of the RAO horse 
    As pollen and mold counts increase in the environment, horses with RAO will experience more symptoms or episodes of RAO. Often barns and stables are not designed with proper ventilation in mind. This contributes to a continual exposure of the horse’s respiratory system to particulate matter. Hay and straw bedding ideally should always be stored in a separate building from where horses are housed, and certainly not overhead. Additionally, the stalling area should be separate from the riding arena. All the dust that is kicked up while horses are exercising can greatly exacerbate the problem. Ever think about how much dust is stirred up into the air while the barn aisles are being swept? Ideally all of this dust exposure should be minimized and RAO affected horses removed from the barn whenever dust is stirred up. One of the best changes to management practices of the RAO horse is simply to house them outdoors. Often an improvement in airway function is seen within days.
    While horses stabled inside are clearly more likely to be exposed to particulate matter, horses on pasture during the summer can also have trouble. This even has its own nomenclature,  summer pasture associated obstructive pulmonary disease or SPAOPD. Horses with this syndrome should be kept off pasture during the summer months, but can be housed outdoors during the rest of the year. If horses must be housed inside, whether they are SPAOPD or perhaps competitive horses that must be stalled, it is imperative that the environment is as dust free as possible. Straw bedding may not be a great choice for RAO horses but shavings can also contain molds similar to those in hay and straw. High quality straw may actually be lower in spore count that some shavings. Alternative beddings may yield the best results such as cardboard or newspaper pellets. If straw or shavings are used, remove any RAO affected horses while bedding is introduced into the stalling area. Essentially, let the dust settle before the horse is put back into the stall!
    Feeding management
    Ideally the RAO horse should graze fresh pastures as much as possible, but obviously this is not always possible.  One of the most immediate dietary changes for the affected horse is to absolutely eliminate any moldy hay or straw that may be in the horse’s environment. While moldy hay should never be fed to horses, it is more critical with RAO horses.   One of the difficulties in finding suitable hays for RAO horses is that humans may not always be able to detect the presence of mold if it is not obvious. Try to find hay sources from a knowledgeable producer who bales high quality hay. The type of fungus which produces the most damaging fungal spores prefers relatively hot temperatures. This would be seen in poorly cured hay, or hay that is baled at too high of a moisture content. The heating which occurs during spoilage is a haven for these fungi.  Round bales may not be an ideal choice, unless they are stored completely inside and are never subject to any sort of spoilage. Additionally, round bales encourage the horse to almost bury their head within the bale, making the immediate breathing area of the horse very dusty. Completely pelleted diets might be a good choice for these horses at it greatly eliminates the dust exposure to the horse while feeding. The quality of the pellet is also critical. Uncoated pellets may break down more easily and have a substantial dust component. Hay cubes and haylage are also alternative feeding strategies.   Moistening the feed can also help in dust suppression prior to feeding. Hay only needs to be soaked for 30 minutes to achieve optimal dust suppression. Beyond that time no additional benefits are seen. However, the down side to soaking the hay is that some of the nutrients are leached out into the water, including P, K, Mg and Cu.
    Beyond eliminating dust and molds other dietary therapy may be aid the RAO horse. Supplementing RAO horses with additional anti-oxidants in the diet may be helpful. There is an increase in free radical formation or reactive oxygen species (ROS) in horses with lung inflammation. In fact, the increase in RAO may increase the upregulation of genes which produce inflammatory factors such as interleukins. Horses with RAO given a supplement of vitamin C and E plus Se resulted in less airway inflammation and an increase in exercise tolerance. Other natural sources of anti-oxidants such as sorghum and omega 3 fatty acids have not yet been studied for their effectiveness in RAO horses.   Additionally, due to the increased energy requirement just to breath, RAO horses are often underweight. The sustained stress to the horse’s system may also contribute to this weight loss. You may need to find a feed with an increase in energy density, such as a fat added feed to help maintain its body weight as well as additional anti-oxidants.
    If one follows these management guidelines carefully, RAO horses may be symptom free for years to come.   While pasture is ideal for RAO horses, performance horses which need to be stalled can be kept healthy with a rigorous adherence to maintaining a dust and mold free environment and proper dietary management.

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