Obesity of the modern horse: a review
In the developed country of today, horses, just like peoples, tend to be more obese than before. Horses are not used to work long hours to plow the land or to transport the family from point A to point B. Today, they are more companion’s animal just like dogs and cats, except for the fact that they can’t sleep on the bed. Some are still used in a business purpose like with some competition animals, but most of the horses are now leisure horses. This mixed with the fact that today’s horses are not in the same precarious environment as their ancestor has created a new problem for them: obesity. More and more horse today are kept on light to moderate exercise and have access to really good feed all year long, even in winter. They are now companion animal, that their owner loves so much, they are well cared for and even sometimes, maybe too well cared for. It is important to understand this problem because it can have a great impact on horses’ health. To understand the problem, we must know every part of it. First of all, it is important to know what exactly is the definition of an obese horse and how to assess his body condition. Then, it is important to know what can cause obesity, what the consequences of this problem are and how to manage it. The last point is really important especially because bad weight lost program can have severe consequences. It is also important to know what a healthy weight is and what to do after the healthy weight is achieved. All those facts will help to understand and manage obesity, in an attempt to avoid or to reduce the prevalence of this serious problem among the horses' population.
To be sure that everybody starts at the same point, let’s look at basics. Horse owners often assess their horse's body condition wrong, thinking that fleshy horses are the normal healthy weight and often saying that their clearly obese horses are just a bit fleshy. So it is really important to learn how to objectively assess their horses’ weight.
By definition obese is: very fat; corpulent (Canadian Oxford Dictionary, 2014). An obese horse will have big fat deposits all over his body. There are many ways to assess the condition of a horse’s fatness: body condition scoring, cresty neck scoring and weight formula. For a more accurate result, all of the tools discussed above can be used at the same time to monitor the weight and fatness of a horse.
The body condition scoring (BCS) is probably the most used tool to assess a horse's body condition, be it for poor or for obese body condition. There are two charts: the 9 points score and the 5 points score (Cavanagh and Turnan, 2014). The most used one is the Henneke et al. (1983) chart that classifies horses within 9 categories: poor, very thin, thin, moderately thin, moderate, moderately fleshy, fleshy, fat and extremely fat (NRC, 2015). For more detail refer to the figure 1 below.
To assess body scoring, 6 points of the horse body are observed and palpated by the observer: neck, withers, loins, tailhead, ribs and shoulder (see figure 2 below). Those regions are called fat pads and are the one where fat build up the most (Cavanagh and Ternan, 2014).
Observer should be careful to look only at fat pads and does not mix up with muscle (Cavanagh and Ternan, 2014), as some breeds have really big muscle mass, but no fat over it.
The cresty neck scoring (CNS) is the assessment of the fat deposit along the crest of the neck. This scoring chart is pretty new to the equine world. Some researchers have shown evidence of a correlation between high crest neck fat deposit and metabolic disequilibrium (Silva et al. 2015). BCS is a great tool to assess the obesity of the horse and CNS is a great tool to assess the risk of metabolic diseases (Silva et al. 2015, Frank, 2011). On the other hand, CNS should not be used alone, as some breeds or sex have facilities to build cresty neck even at a healthy weight. Neck crest fat deposit is also believed to be a long-term fat reserve that can be used when food is less available. Some evidence is showing that it can adapt following the seasonal metabolic rate change (Giles et al. 2015). So CNS is a really great tool that can help you to know which horse will need more monitoring for metabolic diseases, but for obesity assessment, it will be better to use it with the other methods.
CNS can be assessed as seen in the figure 3 below. CSN over 3 are the scores that need more monitoring, over that limit, there is an increased risk of laminitis (Giles et al. 2015) or metabolic syndromes.
This tool will not be as useful as the two above to assess if the horse is overweight or not, as like humans, horse will have different bone stature or height meaning that their healthy weight will be different from one to another. The weight estimation formula will be most useful for two really important points: Calculating the daily ration of a horse and keep a track of the evolution of the horse’s weight ( keeping a track of the weight loss or gain).
There are two formulas used to assess the horse weight: heart girth + measure of the point of the shoulder to the point of the hip or heart girth + measure of the point of the shoulder to the most far point of the rump (Cavanagh and Ternan, 2014). Those formulas work for horses, ponies and draft breeds. Miniature horses have their own formula. Horses’ formula is available in both inches and centimetres but those in centimetres will be used here, as centimetres are more precise.
Horse formula (measure in cm):
Body weight (BW) in Kg +/- 10% = ((heart girth)² * length to rump) / 11880 or ((heart girth)² * length to hip) / 8717
Miniature formula (measure in inches): BW in pounds +/- 5% = (9,36 x heart girth) + (5,10 x length) – 348,53
** These formulas are not accurate for foals and pregnant mares (Cavanagh and Ternan, 2014).
To keep a good track of the horse weight variation, make sure to always measure from the same points. That is to say don’t measure one day from the top of the withers and the next day just 1 inch of that spot, the variation in wither height (especially with high withered horses) will produce false results. They horse may have kept the same weight but the change in measurement spot will have changed the measures.
One of the most important causes of obesity is overfeeding. Overfeeding means: giving too much feed (often ad libidum) or giving feed that is too rich (energy-dense feed). Most of the horses today do not spend more or equal quantity of calories than they consume (Shea Porr and Crandell, 2008, Loving, 2009). When a horse eats more energy than he needs, the body will start to store the excess energy in the form of fat (NRC, 2015). People tend to give high energetic feed to horses (concentrates) and often they contain ingredients that are high in starch. Starch and sugary aliments are easy to digest by horses as they are made of non-structural carbohydrates that are easier to break down compared to complex one from hay (NRC, 2015). As they are such an easy access source of energy for horses, aliment that creates a high glycemic index like starchy aliments are often too rich for the majority of the leisure horses (Johnson et al. 2012). Moreover, horses today have access to lush pastures that are often so nutritive that it exceeds their needs in energy and proteins (NRC, 2015). They are in the pasture all day long and can eat as much as they want, which often result in obesity. Horses have originally evolved to graze and survive on poor pasture (Shea Porr and Crandell, 2008), this can explain why today’s horses that are kept on a really abundant and high quality hay/grass have so much obesity or laminitis problem.
Horses today have easy access to feed, often not a lot of space to move around (or almost nothing when looking to 24/7 stalled horses) and often live in hypo stimulating environments. This can lead horses to boredom. When they are bored, horses can eat way more than they need because it’s the only thing they have to do (Loving, 2009). When horses are housed in more stimulating environment they can spend more time doing other activities than eating (see how to manage the problem section for more information).
Another really important contribution factor for prevalence of obesity today is that horses do not exercise enough. They have evolved to cover several kilometres per day while grazing or to find water or new safe area to eat (Shea Porr and Crandell, 2008). In nature, equids are always travelling around for a reason or another. Today, horses are often fed in feeders that are always at the same place, on a small area where food and water are close to each other, so they have no reason to move a lot. Some are kept on a stall all day long and get out for training or for turnout of four hours a day. They receive high quality feed and they are kept on stall or small paddocks that do not encourage them or give them the chance to make voluntary exercise (NRC, 2015). The majority of them are leisure horses that do not make “forced” exercise (riding or lunging) so often either.
Some horses have a genetic predisposition to obesity. It’s not that there is a gene that makes them obese, it’s more about the way they evolve and the environment in which they evolve that make them more prone to obesity. Most of the breeds that are prone to obesity (ponies or horses) have often evolved in rigorous climate, where winter was harsh or were facing drought in summer. In time of extreme cold, digestible energy given to horse should be raised by 2,5% for each degree Celsius below -15°C (Cavanagh and Ternan, 2014). As such increase in feeding wasn’t really possible back in time, horses that were good at storing fat easily (easy keeper) were the ones that had better chance to survive and to be useful. The same could apply to horse confronted to drought: feed was less available and less nutritive. As mares with poor body condition (fewer than 5 BCS) have lower fertility rates and have fewer chances to carry a foal to term (Cavanagh and Ternan, 2014, NRC, 2015), easy keeper mares were those who had better chance to reproduce and to transmit their genetic material. This is probably why some breeds have such a tendency to obesity, the foundation mares that created the breed were probably a bunch of easy keepers.
Horses that were insulin resistant were also advantaged in those climates (Treiber et al., 2006) because the condition is probably caused or linked to some “thrifty” genotype (Kaczmarek et al., 2016). This was related to obesity, which gave them some “reserve” for the hard winter.
Just to give some example of this type of “easy keeper” prone to obesity breeds, let’s just think about the Canadian Horse, the Shetland pony or the Welsh pony.
Metabolic syndrome could be placed in both cause and consequence of obesity. It’s a bit more like a vicious circle: Obese horses are more prone to metabolic syndrome and horses with metabolic syndrome have more difficulty losing weight (Loving, 2009). Obese horses are more prone to the equine metabolic syndrome (EMS) because adipose cells react to endocrine signals, the more we have adipose cells, the more the horse has a chance of hormonal irregularities (Loving, 2009). On the other hand, those horses have difficulty to lose weight because of a better metabolic efficiency (Frank, 2011), they tend to do more with less. That is to say that they tend to take better advantage of their food than “normal” horses (Frank, 2011) so even if they are fed less, they tend to stay overweight.
Equine metabolic syndrome is not a disease in itself, but a clinical syndrome associated with some diseases. In fact, it’s a set of risk factors that predispose the horse to other diseases (Frank, 2011).
Seasons can affect horses prevalence of obesity. Why? Because back in time, horses had to make some energy reserves in the form of fat in anticipation of the winter. Indeed, as they had not always access to a good quantity or quality of food during winter, horses were programmed to make some reserve at the end of the summer (Loving, 2009). Fortunately, horses do not lack of feed during winter anymore, unfortunately their metabolism has not adapted to this fact yet (Loving 2009) making horses more prone to obesity at the end of summer (or early fall) and not losing this extra weight anymore during winter.
Insulin resistance (IR) is probably one of the most important consequences of obesity. There is some evidence that IR can be promoted by obesity (Loving, 2009), but there is also some evidence that relates obesity to feeding carbohydrates rich food (Loving, 209). As obese horses often receive too much energy-dense food, both reasons can raise their chance of developing IR.
IR is the reduced capacity of the body tissues to capture the glucose from the blood stream (Loving, 2009). Because the tissues become less responsive to insulin, the body then starts to increase the level of insulin secreted so the tissues will receive a stronger signal (Shea Porr and Crandell, 2008). So when tested, those horses will have increased levels of insulin in their blood. Stress can also raise the insulin level in the blood so it will be important to look with the veterinarian if the increased level of insulin in the blood is due to IR or to stress (if the horse needs to quit the barn to pass the tests for example).
Laminitis is also one of the most important and frequent result of obesity. It has been put under IR because it can be a prevalence factor of development on laminitis (Shea Porr and Crandell, 2008), EMS can also lead to laminitis (Loving, 2009), but at the end, it all comes the dominant factor for all those diseases: obesity. A direct link between obesity and laminitis is the fact that all that extra weight will overload the horses’ hoofs, which can create bruises and inflammation into them (Loving, 2009).
Laminitis is a general term which refers to an inflammation of the laminae of the equine hoof (Loving, 2009). In more advanced case, the third phalanx can detach from the hoof wall because of the too important laminae inflammation (the link between the phalanx and the hoof wall is weakened) and rotate. In worst case, the phalanx will rotate to such an extent that it will perforate the sole. So laminitis can be really painful for a horse and even life threatening.
Once laminitis is developed, it will be really important for the horse to lose weight as mechanical overload of the foot by excessive weight will aggravate the problem (Loving, 2009).
* An important point to note is that laminitis can have other factors that are not related to obesity (ex: retained placenta), even if they are less frequent, they are not impossible (Loving, 2009).
Obesity or overfeeding of the foal can have a really important part of the development of DOD (Loving, 2009). Overfeeding can also raise the chance of DOD development even before a foal is born. Indeed, overfeeding of the dam can raise the chance of the foal to develop DOD (Loving, 2009). Obesity will put too much weight on the growing bones of the foal, causing them stress. DOD is a group of diseases which according to Cavanagh and Ternan (2014) include: physitis, osteochondrosis, OCD, wobbler’s syndrome and angular limb deformities.
Overfeeding will give so much energy to the foal that it will allow him to grow at a faster rate than a normal fed foal. Rapid growth rate will enhance the chance of a foal to develop DOD (Huntington, 2012, Cavanagh and Ternan, 2014). Moreover, obese foals often fail to become good athletes in the future (Huntington, 2012). So it will be really important to resist the temptation to overfeed dams and foals. Seeing ribs is normal on a foal, people tend to think they are too thin but they are often just perfect. If we can see ribs but the foal has a great muscular mass on his body, he is not skinny. A new theory has emerged and found interesting correlations between DOD development and cartilage sensitivity to insulin (Huntington, 2012). This could give a new reason (not if there is a lack of it here) to avoid giving feed high in non-structural carbohydrates (concentrates) as those types of feed create a high insulin response due to an increased post-feeding glycemia.
Stressed joints are a consequence of obesity as more body weight put more pressure on the articulation (Loving, 2009). It’s a simple physical fact, a weight-bearing surface will distribute the pressure evenly, when more weight is putted on that surface, the pressure will increase. So if an articulation needs to bear more weight it will receive more pressure. According to Loving (2009) the smooth and shiny articular surfaces degenerate when they are irritated by an overload. So the cartilage will be more and more damaged as the load increase (Loving, 2009).
Obese horses are often intolerant to effort (Loving, 2009), they get tired more easily and have a less good cardiovascular health. An obese horse fat deposit is the reflection of an insufficient overall fitness (Loving, 2009). When the horse will start a fitness training program, muscular mass will replace adiposity.
As body fat is a great insulating, obese horses are more prone to heatstroke and hyperthermia (Loving , 2009, Tighe and Brown, 2004). Indeed, their abundant fat deposit will not dissipate the heat effectively. Moreover, the fact that they have to carry all that extra weight will require more energy from them and will be more tiring accentuating the need to dissipate heat (Shea Porr and Crandell, 2008).
An intestinal lipoma is a fatty tumour which develops in fat (Loving, 2009) so an obese horse will have prevalence for developing this type of tumour. Horse over 15 years of age will have higher risks to develop a lipoma (Shea Porr and Crandell, 2008). Although this type of tumour is a benign one, there are still some health risks about it. This type of tumour often develops in the mesentery which supports the intestine. They then hang there and can easily move and flip in such a way that they can create a strangulation colic (Shea Porr and Crandell, 2008). There is no need to say that this is really dangerous, even deadly for a horse.
Obesity can lead to problems regarding breeding animals. Obese horses may encounter some irregularities regarding metabolic and endocrine regulation (NRC, 2015), which can play a role in reproduction. For stallions, it can even lead to infertility (Tighe and Brown, 2004). For obese mares it is the contrary, mares with BCS fewer than 5 will have more infertility or more difficulty to carry a foal to term than obese mare. The ideal weight for a broodmare is a BSC between 5 and 7 (Frape, 2010) but a mare that has a BCS over 8 will not be better nor worst broodmare than those between 5 and 7 (Frape, 2010). Cavanagh and Ternan (2014) for their part found that “In broodmare, obesity over 7 has been associated with prolonged luteal phases and lengthened interovulatory intervals so it can have an impact on reproductive performance”. So the opinion on that is still somewhat mixed.
Where there is a certainty of obesity causing problems to broodmare is with parturition. As seen previously, obese horses have intolerance to efforts. So when obese mares are foaling, they can be tired more easily (Frape, 2010) which can be life threatening for foals and for themselves.
Diabetes Miellitus (DM) stands in the last place because of its rarity within the horse population, in contrary to humans where it is more common (Johnson et al. 2012). Although rare, it is still possible for a horse to develop this pathology.
DM is characterized by a really high glycemic index (hyperglycemia) that is caused by the horse not producing enough insulin or not producing it at all ( Johnson et al., 2012). The question is: Is the horse less prone to develop DM or is they die from mysterious cause at young age without anyone noticing the DM problem. Or maybe it is not present among equid population because back then, those horses died before they could reproduce so they never transmitted the genetic predisposition for the disease. It’s still a disease that has not been studied a lot.
This section comes first because the first step in a weight lost program is to keep a good track of the horse body condition all along the process. This will allow you to see if the horse is losing or gaining weight. When an owner sees his horse every day, the change in his body condition will be less noticeable as they change just a little bit every week.
Keeping an eye on the progress of the horse will also give the opportunity to adjust the nutrition of the horse in consequence of his weight lost. Some say that the quantity of feed that a horse should eat per day should be based on his healthy weight. But let’s look at the extremely obese horse, this could be a very drastic change for him. So keeping an eye on the weight lost of the horse could help the owner to adjust slowly the intake of the horse fallowing his weight. A slow and steady weight lost is preferable (Shea Porr and Crandell, 2008) as drastic weight lost can lead to some dangerous condition (see consequence of a bad weight lost program section below).
Application to keep track of the horse weight and BCS are available on smartphones. Some are even calculating the formula for weight, the user only has to enter the heart girth measurement and the shoulder to rump measurement. Then it offers a graphic version of the weight curve of the horse. So this can be a great option to keep a track of the progress of the horse.
The first rule for losing weight is that the horse needs to burn more energy than what he is consuming (Shea Porr and Crandell, 2008). Increasing exercise for an obese and unfit horse should always be progressive (Shea Porr and Crandell, 2008). Like in human, extremely obese horses need to go slow at the beginning because of their unfit system, starting with too much and too intense exercise could be dangerous for them. It could produce metabolic problems or heat stress to the horse (Shea Porr and Crandell, 2008). In the first few weeks, really obese horses should be trained in hand and exercised over 10 to 15 minutes of walk with few strides of trot (Cavanagh and Ternan, 2014, Shea Porr and Crandell, 2008). As the horse get fitter and slimmer, exercise can be increased. Owners should follow the rhythm of his horse and look for signs of fatigue. Owners should take a note that walking and trotting burn more energy than canter and gallop (Shea Porr and Crandell, 2008). It is recommended not to raise the intensity of the work before the horse BCS is closer to normal (5-6 BCS) (Cavanagh and Ternan, 2014).
It is interesting to know that moderate and regular exercise can help to prevent IR and laminitis (Frape, 2010) so irregular working program is not really good for horses. That is to say that working the horse regularly for two months then putting him in the field without any work for two other months and so is not a good idea. Metabolic rate change when exercise increase (Cavanagh and Ternan, 2014), so irregularity in an exercise program may cause metabolic problems.
Starting to calculate what a horse can eat is a great way to help him lose weight. There is some important rules to do so: no long fasting period, no fewer than 1,5% of the horse body weight (BW) in fibre and no feeding program that are below the NRC minimal feeding requirement.
Horses should not be fed under 1,5% of BW in fibre, fibre is really important for their digestive tract health (Cavanagh and Ternan, 2014). They have evolved to eat fibrous feed and to digest it in their hind gut. Some are losing weight with 1,75% of their BW in fibre and others with the NRC minimal requirement of 2% BW in hay. For some horses, only the fact that their portions are calculated is enough to make them lose weight.
So to avoid not giving enough fibrous feed to horses, one can choose to give less energy-dense hay. When hay is harvested once mature, it contains less energy so the horse can eat enough hay without receiving too many calories (Cavanagh and Ternan, 2014, NRC, 2015). It is possible to add some chopped straw chaff with the hay so the horse will have a bit more to eat but not much more calories. Another option to reduce the energy density of hay is to soak it, so a good part of hydro-soluble carbohydrates will be removed from the hay (Cavanagh and Ternan, 2014, Loving, 2009). When this option is chosen, a good vitamins and minerals supplement should be given to make sure the horse has enough of them (this should be discussed with a veterinarian). Indeed, some vitamins and minerals are hydro soluble as well. To be sure the horses receive enough vitamins, minerals, proteins, etc. refers to the NRC minimal requirement. They should receive the minimal requirement for the entire categories, only the digestible energy (DE) can be reduced a bit (Shea Porr and Crandell, 2008, Loving, 2009).
Avoiding long fasting period is essential for the horse, because it will create boredom, stereotypies and because it is not good at all for their digestive tract that is made to receive a constant supply of food (Cavanagh and Ternan, 2014). In addition to the strategy of giving more hay that is less energy dense, some slow feeding strategies can be used. Using good quality hay nets can be a really interesting way to reduce the speed at which the horse eats his hay (Glunk et al., 2014) while making it more challenging, so it is a good mental occupation for the horse. Make sure to follow the company instruction on how to introduce the hay net to your horse. In addition to the hay net, feed multiple times a day will also help (Shea Porr and Crandell, 2008).
It will also be necessary to reduce to a minimum or even to avoid completely to feed concentrates to horses (NRC, 2015). If the horse receives a good quantity of it, reducing the amount over several days will be a good option. Most of horses do not need the extra energy and calories of concentrates (Shea Porr and Crandell, 2008). If there is any lack in the ration, vitamins and mineral supplements can be used. Note that ration balancer can be more caloric dense than people think, the supplement can be preferable to the balancer. If the hay is under 8% of protein, it can be balanced with a protein supplement that is low in non-structural carbohydrates (Cavanagh and Ternan, 2014).
It is important to control the grazing of a horse to help him lose weight. As seen previously, pasture often exceeds DE requirement for horses. So overweight horse that has access to pasture will need some restricted grazing time or to wear a grazing muzzle to reduce the total food intake (NRC, 2015). It is important to know that the sugar levels of grass change during the day: the sugar level peak is in the middle afternoon and the lowest level is at the middle of the night (NRC, 2015). So it is safer for a fat horse to graze at night and to be removed from the pasture during the afternoon. Sugar level also changes during seasons: fructan is present at a higher level at spring and fall (Loving, 2009). This is because when the soil temperature gets lower sugar rise into the stems of the grass.
If removing the horse during the sugar peak periods is not possible, buying a grazing muzzle could be a good option to help reduce the intake of the horse while letting him graze constantly (Loving, 2009). A previous research from Longland et al. (2011) found that grazing muzzle reduced voluntary intake by 83% but a recent study from Glunk et al. (2014) found it was actually reducing it by 29% only. Maybe the quantity of voluntary intake with grazing muzzle can vary among individuals.
A new trend today is the use of what is called “paddock paradise” (PP) to enrich the environment of the modern equid. PP is a new way to conceive paddocks for horses. The starting point is to build a track instead of a square paddock and making a food station, a drinking station and a shelter station, all in different areas of the track. That way, horses are encouraged to move around the track to travel between stations. Instead of going from the hay to the water tub in a straight line, they need to follow the track. The track can also be built with different types of soil covering; it can be rocks or even safe logs that the horse needs to step over. These things can make the environment more interesting for the horse and can help him have other activities than eat all day long in addition to encourage movement.
Horses should also be offered the longest turnout possible with congeners. Walking is primary to their intestinal health because it fastens the intestinal motility. Congeners are also important for a lot of reasons but principally because horses are social animals that are happier when they can interact with other horses and also because being around other horses will encourage them to move more and play.
Some feeding toys can also be added, or simple toys like balls or even just plastic cane filled with rocks so horses can spend time exploring new things. Changing the toys regularly will help to keep interest of the horse. This can be a playful way to occupy horses’ time and to make a despooking activity at the same time.
Losing weight is important for the health of a horse, but doing it the wrong way can be as damaging or even more than keeping the horse obese. So it is important to know what needs to be avoided having a healthy weight lost program.