Changing your horse's diet
At some stage, all horse owners will find it necessary to change their horse’s diet for any number of reasons, which might include changes in temperature, season, stage of growth, pregnancy or a change in performance level. When changing a horse’s diet, however, great care should be taken, both to avoid any digestive upsets, and to give the new feed a chance to work.
Whether it is the concentrate feed, the hay or the pasture that is to be changed, colic or laminitis could occur if the diet change is not planned properly and not done over a period of time.
The science
Fermentation occurs in the hindgut of the horse and it is not only complex, but also a very delicate process. Fermentation is key for optimal digestion of feedstuffs, and ultimately the production of energy. This process can be disrupted by multiple factors, change being one of them.
There are billions of protozoa, fungi and bacteria living within the horse’s gut, and it is these microbes that are responsible for the fermentation of carbohydrates into volatile fatty acids for energy. If a badly planned change of diet occurs, it can ‘shock’ or change the population of these microbes, the rate of fermentation, and thus the by-products of the fermentation process. In addition, disrupting normal fermentation can lead to rapid changes in the pH (acidity) of the intestine, which can further negatively impact on the normal microbial population and the whole digestive process.
To maintain the delicate balance in the gut, the following guidelines may help when altering a diet.
Altering the amount of feed
Any increase or decrease in the amount of concentrate given to a horse should be added or removed at approximately 200g per day (not more than 250g) until the desired amount of concentrate is reached.
When introducing a new type of hay or new brand of concentrate
The new hay or concentrate should replace the old feed at a rate of 25% every other day, taking a total of seven to 14 days for the new feed to be fully implemented. Feed intake, or eagerness to consume the diet, may decrease during this changeover period. If this occurs, more time may be needed for the horse to adjust to the new feed.
Change in pasture
When a horse is turned out on new pasture, especially where the pasture is lush and green, the time on the pasture should be gradually increased to avoid overeating. The time on the pasture should be increased by one hour each day for four to five days. Some horses take more time to adjust to dietary changes than others. It is important, therefore, to monitor the horse’s eating habits and health status carefully during this time.
Changing to a high-fat diet
As with all new feed additions, horses should be slowly introduced to added oil/fat. Start with a small amount (20-60mℓ), increasing by 20-40mℓ each week, until the desired level is found. This may sound slow, but it allows the horse’s digestive system to adapt to the fat, which will reduce the likelihood of soft manure, a typical, though usually transient, effect of using oil. It is important to note that complete metabolic adaptation to a high-fat diet has been shown to be achieved in 11 weeks, but not in six weeks (Custalow et al., 1993). Therefore, keep in mind that it will take a while before all the positive benefits of a high-fat diet will be noticeable.
As with all new feed additions, horses should be slowly introduced to added oil/fat. Start with a small amount (20-60mℓ), increasing by 20-40mℓ each week, until the desired level is found. This may sound slow, but it allows the horse’s digestive system to adapt to the fat, which will reduce the likelihood of soft manure, a typical, though usually transient, effect of using oil. It is important to note that complete metabolic adaptation to a high-fat diet has been shown to be achieved in 11 weeks, but not in six weeks (Custalow et al., 1993). Therefore, keep in mind that it will take a while before all the positive benefits of a high-fat diet will be noticeable.
Feed by weight, not volume
When changing to a new concentrate feed, it is important to ensure that the correct weight of the new feed and the feed scoop used are aligned. It is very important to ensure that horses are fed the correct portion of food by weight, and not by volume! All feeds have different densities, and a scoop of one type of feed may not weigh the same as a scoop of another feed type. Feeding instructions are also always given as a percentage of body mass, so it is very important to establish the exact weight in kilograms of the horse, as well as how many kilograms the scoop holds of the specific product being fed.
Failing to establish the correct weight of the portion being fed can lead to considerable over- or underfeeding, especially when changing to a new concentrate. Overfeeding can lead to the horse becoming obese, which will take time to rectify, but, more seriously, it can also cause severe colic. Underfeeding, especially of performance horses, may lead to a lack of energy or even severe weight loss. While this can be rectified fairly quickly in healthy horses by feeding the correct quantities, often time is lost, because the reason for weight loss or low energy levels is often sought elsewhere first. For example, the owner feels the product is not working, when in actual fact it is the incorrect amount that has led to the weight loss. Always begin by checking that the horse is fed the right amount by weight.
The list below illustrates just how easily the incorrect amount can be fed, especially in a stable yard where more than one product is used.
A container holding 5ℓ of water will hold approximately:
1.5kg chaff-type products
3.0kg of a typical pelleted horse cube
2.9kg crushed maize
1.6kg wheaten bran
0.6kg milled lucerne
6.5kg molasses syrup
This clearly demonstrates how easily one can either over- or underfeed by considerable margins. This does not mean one cannot use the 5ℓ bucket method to feed your horses. Simply weigh out the appropriate amount of concentrate and mark the bucket with a permanent marker to know up to where to fill it each time. This technique allows one to standardise the amount of concentrate fed. Weighing the feed each time, however, is by far a more accurate way.
This also explains why the person responsible for feeding at a yard might be surprised should a horse change from a pelleted product to a muesli-style product. Visually, it may appear that the new feed is being fed at nearly twice the amount of the previous one, but evaluating by weight shows clearly that this is not the case.
Some horses may self-regulate after changing feed
Some horses, especially those in more intensively managed yards, those changing from a low fibre diet, and those in poor condition, may initially rush their food in anticipation, and may actually eat more than what they need. You need to watch out for this! After a few weeks, however, the horse will generally start to slow his eating in order to regulate his body condition, and some may even leave a proportion of food once full. Often this is mistaken for not ‘enjoying’ the food anymore. Reducing the amount of food at this point will usually result in the horse once again eating all the food given.
Alternatively, allowing the horse the entire evening to eat his feed will often also result in all food being consumed. Horses are designed to eat little and often, so a slow eater is never a bad thing.