It can be difficult to know what your horse’s dietary needs are. Sometimes it seems simple enough if a horse has access to a lush paddock, but even then, deficiencies can very well develop with consequential health issues.
What is special about the horse’s GI tract?
To understand why horses have certain nutritional needs we need to look at what they were built for. Horses evolved to live on the dry steppe, where they adapted to the low energy, high fibre food that was available to them. They were built to graze and browse for food for most part of the day to make sure they survived. Their intestinal tract adapted to this continuous slow supply of harsh dry fibrous plants. The horses we now breed stem from those ancestors and still have some of the same anatomical and physical characteristics that their ancestors had. Some important examples are:
- Unlike humans and many other animals, horses have a continuous production of stomach acid. This means that instead of producing more stomach acid when food is being consumed, the horse’s stomach produces acid continuously, whether or not there is food available. When the content of the stomach acidifies too much, this causes stomach ulcers. Normally, the acid is buffered by the saliva that’s swallowed when a horse eats. An adult horse produces about 35-40 litres of saliva every day. Regular saliva production keeps the stomach content from acidifying too much. The ancestors that our horses stem from grazed almost continuously, so this continuous acid production actually made their digestion more efficient. They never had a break from grazing long enough for their stomachs to acidify. Research has shown that ulcers can already start to form when a horse has no food for longer than 6 hours.
- Only the horse and the rat are known not to have a gall bladder. The bile that’s produced therefore isn’t stored until food is passed in the intestinal tract. Instead, it is continuously secreted into the gastro intestinal tract, because “in the old days” horses would always have some food passing through. Bile helps digest fats in the diet.
- Horses are hindgut fermenters. Their hindgut is the home of a wide variety of bacteria, fungi and protozoa, which the horse depends on with his life. Without the hindgut’s microflora, the horse would not be able to break down the fibre that normally supplies the horse with about 80-100% of their daily energy requirements (depending on the level of exercise). The various kinds of bacteria, fungi and protozoa in their hindgut live in a balanced ecosystem. When this is disrupted, this causes digestive disorders which can lead to colic and/or diarrhoea. In fact, colitis, a condition in which the hindgut microflora is disrupted, can cause a horse to die. The microflora in the hindgut need the right environment for their ecosystem to stay balanced and functional. For this they need a regular supply of fibre and the hindgut needs to have the right pH. Things that upset these things can cause the horse to become ill. When a horse has a low-grade chronic imbalance of the hindgut, the gut can’t cope with small changes as well and the risk of colic increases. This can cause discomfort or recurrent spasmodic or tympanic colic issues. If a horse’s poo often seems a bit too soft or there’s always a squirt of water at the end, this may indicate the horse has a low-grade, chronic hindgut problem.
So now you might understand why horses have an innate(born), inner drive to…
- eat almost continuously except when they sleep, rest, drink or move
- want to eat fibrous feeds, such as grass or hay
- have a need to move as they graze/eat
- prefer eating together as a group
This innate, inner drive is called a “behavioural need”. This drive or need is strong, because it’s necessary for survival. It motivates wild horses to travel 40km a day to get to food! When horses can’t fulfil their “behavioural needs”, this causes stress and leads to behavioural issues, such as stereotype behaviour. For example, horses that can’t spend enough time eating fibre often develop issues such as windsucking, wood chewing, bruxism (teeth grinding), etc. This can also happen when they see other horses eat but they can’t join in because they’ve not been fed themselves.
We have not yet mentioned the small intestine. The small intestine is where carbohydrates, sugars, fats, proteins and minerals are digested and absorbed. When a horse eats too much of a feed that contains a lot of carbohydrates and/or sugars, the small intestine can’t cope with the supply and part of it will be passed on to the hindgut unprocessed. Special mention should be made of fructans, which are a type of simple sugars that cannot be digested properly in the small intestine and cause issues in the hindgut that can lead to laminitis. Unprocessed carbohydrates and sugars from the small intestine disrupt the bacteria and protozoa in the hindgut, which causes irritation of the gut (diarrhoea and/or spasmodic colic) and the bacteria that try to ferment these nutrients produce too much gas (tympanic colic). These issues don’t just arise when a horse is offered too much hard-feed, it can also happen when a horse is moved to a new pasture or when the grass contains too much sugars (more about this later). Dietary changes (whether you introduced them, or mother nature did through the grass) can disrupt the gut up to 2 weeks after. When feeding hard-feed, it is important to be careful with the portions you offer your horse. Horses cope better with multiple small feeds then one big one. That way the stomach has enough time to digest everything, and smaller portions give less extreme sugar and insulin spikes in the blood, which resembles the natural situation better.
Grass in the diet
The grass most horses graze on is much higher in energy and much lower in fibre than what the horse was designed to eat. This causes a lot of health issues for our horses that we need to stay on top of. There are different kinds of grass. Most horses in our region are on Ryegrass and clover, which is essentially made for cattle that need to eat a lot of energy to produce milk or grow meat. On a nice pasture, a horse can eat its entire daily energy requirements in just 2-7 hours (depending on breed, the pasture, season and grazing behaviour). When the dry matter content of grass is compared to hard-feed, it resembles feeds made especially for lactating mares that have a high demand of energy. On other words, if a horse is grazed on lush pasture, we need to make sure the horse doesn’t become obese, insulin resistant, laminitis, etc.
To keep your horses healthy, make sure you know the basics of grass and pasture management.
So now that you know more about how to keep your pasture safe for horses, let’s talk about the nutritional value for the horse. On average a horse eats about 0.16kg of dry matter per 100kg bodyweight per hour. So, if your horse weighs about 550kg, it eats about 21.12kg dry matter grass per day. The dry matter content and Digestible Energy (DE) per kg dry matter (DM) is as follows:
| Ryegrass/white clover dominant | DM | DE(MJ)/kgDM |
| Pasture, spring | 12-15% | 14.2-15.4 |
| Pasture, summer | 15-20% | 11.7-13 |
| Pasture, summer dry | 20-30% | 11-12.3 |
| Pasture, autumn/winter | 13-18% | 13.6-14.2 |
Source: www.dairy.co.nz
To compare:
- Dunstan Breed & Grow nuts for broodmares and young growing horses has a DE of 13MJ/kg DM.
- NRM Evolve nuts for pregnant and lactating mares as well as young growing horses has a DE of 12MJ/kg DM.
- Dunstan All 4 Feet for horses prone to laminitis has a DE of 10MJ/kg DM.
- NRM Equine Balancer nuts for horses that currently have laminitis or to be fed as a vitamin-mineral supplement, also has a DE of 10MJ/kg DM.
Side note: Dunstan All 4 Feet is a “low GI” feed (meaning low “Glycaemic Index”). The energy sources are mainly other things than sugars and starch, so that the glucose and insulin levels in the blood after a meal don’t go up as much. This means lower insulin spikes and thus less risk of causing laminitis in a horse that is at risk. NRM Equine Balancer is a vitamin-mineral pellet feed, so it doesn’t contain extra energy sources, only vitamins and minerals. It can be used when extra energy isn’t needed, so as a supplement to balance out nutrients, when a horse needs to lose weight, or when a horse is suffering from laminitis. Where Dunstan All 4 Feet is meant to be fed as 3kg per 500kg horse and therefore adds up to 30MJ daily, NRM Equine Balancer is meant to be fed as 0.5kg per 500kg horse which adds up to 5MJ daily. All feeds have their purposes. These were just used as an example.
You can see why spring and autumn can be risky periods for horses! We tend to see more cases of both colic and laminitis in these periods.
Caloric intake and essential nutrients
So, if your horse weighs about 550kg, it eats about 21.12kg dry matter grass per day, which equals to about 243 to 275 MJ in summer and 285 to 327 MJ in autumn and spring. A 550kg horse that’s spelling needs about 77MJ on a daily basis and performance/show horse of 550kg would need about 110MJ per day (source: www.msdvetmanual.com). You can see how much 24-hour grazing goes over this requirement if we don’t somehow restrict their intake.
A lot of horses we see are overweight or even obese. Many owners try to reduce intake by keeping their horse on a very short pasture and feeding them hay. As we have explained, very short pastures can still have a very high sugar content and a very low nutrient content, so that the horse is completely reliant on hard feed for essential nutrients, which “easy keepers” and horses with weight issues often don’t get a lot of. This creates a situation where the horse doesn’t get enough essential nutrients to keep its body healthy and youthful. Options to manage these situations would be to fertilize and manage your paddocks properly, strip graze to reduce grass intake (which also helps maintain a good pasture and makes removal of faeces easier), feed hay so that your horse gets enough fibre, and add a good quality vitamin-mineral supplement. If a horse needs to lose weight, a different approach would be needed, so give us a call for advice.
We’d also like to mention that if you’re feeding your horse a hard feed, but less than the advised dose on the package to reduce caloric intake, you’re also reducing the vitamin and mineral intake to below advised levels. If that’s the case, it’s better to switch to a low-calorie hard feed or a vitamin-mineral pellet feed. Horses that are grazed unrestricted also need supplementary nutrients, because as we’ve explained nutrients in grass are often (too) low. In wintertime, the digestibility of grass goes down as well, meaning that of those nutrients that pass through the GI tract, not all of them can be utilized.
Not all hard feeds and supplements contain adequate vitamin-mineral content. Best way to know for sure is to compare the product’s content to the horse’s daily needs. Our vets can do a diet analysis for you to see if your horse’s diet is adequate.
Tip: A good product will say exactly what and how much it contains on the label, so that you or your vet can check whether your horse is being supplemented adequately. Your horse should at least receive all essential nutrients daily (Table 1).
The 6 elements of a horse’s diet
A horse’s diet should always be assessed for the following components:
- Fibre: of paramount importance to gut microflora, largest energy source for the horse.
- Energy: gut bacteria make free fatty acids available from fibre, which accounts for most to all of the energy requirements. If not enough, then add more fibre (hay/bailage) or hard feed.
- Protein: mainly from grass. Can come from hard feed. If not enough, horse loses topline etc.
- Vitamins: A and E from grass, B from gut bacteria, C from liver, D from sunlight.
- Minerals: from grass, but most times deficiencies develop if not supplemented.
- Water: needs to be clean and fresh. Make sure you clean troughs regularly, keep ducks from pooing in the drinking water and make sure there’s never any dead animals in it (botulism).
When it comes to proteins, here’s what you should know…
Proteins are built up out of amino-acids. There are 20 different amino-acids, which are the building blocks that together can make up a lot of different kinds of proteins. Of these 20 amino-acids, the horse can make 11 amino-acids by itself. The other 9 are what we call “essential” amino-acids. Horses can’t make them, so it’s essential for the horse to receive them through the diet. When an essential amino-acid is missing, the entire production of a protein can’t go through, even if there’s a lot of other amino-acids available. You might be feeding your horse lots of protein, but as long as there’s not enough essential amino-acids to complete the picture, the other amino-acids would just be lost unused. This means that a diet can contain a lot of protein, but still be insufficient. If there’s too many proteins in a diet, this can have a negative effect on the gut and performance. The kidneys excrete unused protein, which means that with a large excess of protein the kidneys have to work a little harder.
Of the essential amino-acids, Lysine, Threonine and Methionine are most often deficient in a horse’s diet. How many of which amino-acids a horse requires depends on their body-health, their level of activity, their age, etc. If a horse’s diet doesn’t contain enough essential amino-acids and they need to be supplemented, it’s handy to know that some products contain higher levels of essential amino-acids than others. For example, some supplements (hard feeds) contain extra amino-acids, which they should mention on the label. Soy contains high levels of essential amino acids as well. Soy is often used in hard feeds to add protein content. Copra meal can also be used for extra protein. It’s a by-product of the oil industry and has a high protein content. However, it doesn’t contain a balanced complement of essential amino acids. It’s relatively poor in Lysine, Threonine and Methionine. Extra attention should be made in young horses, which need these amino-acids to grow.
What about minerals?
There are certain nutrients that the horse can’t make on its own, which it needs to receive through its diet. We call these nutrients “essential”. How much a horse needs of these nutrients depends on its body weight, level of exercise and whether it’s young and growing, pregnant or lactating. Here’s a list of essential nutrients:
| Minerals | Trace elements | Vitamins |
| Calcium (Ca) Phosphorus (P) Potassium (K) Magnesium (Mg) Sodium (Na) Chloride (Cl) Sulphur (S) | Iron (Fe) Copper (Cu) Zinc (Zn) Iodine (I) Manganese (Mn) Selenium (Se) Cobalt (Co) | Vitamin A (grass) Vitamin D (sunlight) Vitamin E (grass) Thiamine (Vit B1) Riboflavin (Vit B2) |
The B vitamins are produced by the microflora in the hindgut. If the hindgut is healthy, these vitamins don’t need to be supplied in the diet. Only Vitamin B1 (thiamine) and B2 (riboflavin) always need to be supplied through the diet.
The grass contains variable amounts of these nutrients. If a horse doesn’t receive enough of them through its diet, this will lead to poor health and poor performance. An example is Selenium, which is relatively very low in the grass in the Manawatu area. We recommend to do a Selenium blood test once a year.
Putting it all together
So now you know a little bit about everything. How do we put these things together? How can we make sure your horse is receiving all the nutrients it needs, while fulfilling its behavioural needs and not gaining too much weight?
There is information available on what the nutrient requirements of horses are. They mainly depend on the level of activity and body weight. A horse should have a basic diet of grass and/or hay or bailage to cover the fibrous needs and behavioural needs. If a horse is restricted part of the day it is important to realize that a horse shouldn’t go without something to eat for more than 6 hours at a time. Good grass will contain enough protein. If on hay only, the quality of hay will determine the protein and vitamin A & E content. To make sure the horse gets enough minerals and possibly to supplement protein or vitamins, a good hard feed or supplement should be found. This can be done by using the information about the horse’s body weight, body condition score and level of exercise and comparing the requirements to available products.
If you’re curious to whether your horse’s diet is covering all your horse’s nutritional needs, just reach out to us and one of our vets can help you out.
