Dietary fat: a versatile ingredient
by Dr Derek Cuddeford, Royal (Dick) School of Veterinary Studies, University of Edinburgh
When one thinks of fat in the diet it is usually in the context of feeding carnivores or omnivores and certainly not herbivores! It is important to be clear about what fat actually is. It is any of a group of natural esters of glycerol and various fatty acids, which may be solid at room temperature and are the main constituents of animal and vegetable fats. Without going further and getting lost in biochemistry I think it is sufficient to say that the unsaturated fats that contain double bonds between carbon atoms (C=C) are liquid at room temperature and are known as oils. Good examples are the vegetable oils that we cook with. These oils are relatively unstable and are susceptible to oxidation so they must be stored carefully otherwise they may become rancid. Saturated fats (C-C) are hard fats such as lard and are found in animal carcasses and some plant material. They are stable, only becoming liquid at high temperature.
If we can accept that the natural diet for the horse will be largely grass with some browse thrown in then the fat intake of a 500kg horse eating 12.5kg dry material (say grass hay) will be between 312 to 437 g/day. In the general scheme of things this is not a lot of dietary fat. It should be realised that this fat is unsaturated and thus helps to meet the horse’s need for essential fatty acids. If we move away from a basic maintenance diet such as hay alone and then feed oats and hay as one might to a racehorse this results in a dramatic change in fat intake. If 9kg oats and 3.5 kg hay are fed then the likely fat intake will be between 490 and 525 g/day, up to 1.5 x that consumed from forage alone. If naked (hull-less) oats are substituted for traditional oats then the fat intake from the basic ration would be nearly 1kg /day. Thus, horses fed conventional diets can consume between half and one kilo of plant fat per day, all of it unsaturated! It is clear that the horse is well adapted to dietary fat when it is a component of plant material.
Dietary fat has the benefit that it contains about 2.5x the energy content of starchy concentrate and thus it can be used to manipulate the overall energy density of the diet and also, the overall composition of the diet. We all know that careless feeding of starchy concentrates (too much at one feed, etc) can lead to digestive upset. The use of added fat allows the reduction of starch in the overall diet without compromising the energy supply to the horse and some might then consider the diet “safer”. “Hard” fat (animal tallow) has been tried in horse diets but it is not advisable (low palatability, etc) and when it is solid at room temperature it is unusable! Thus this means that it is only really the vegetable oils that are recommended for use. Plant oils come in a variety of guises. We use the more expensive oils such as olive oil, sunflower oil, groundnut oil, etc in our daily cooking forays into the gastronomic arts. The most commonly used oils added in to a horse’s daily ration by owners are soya and maize (corn) oils. Unlike us, Feed Manufacturers have access to a range of fat-based products that they can incorporate into their horse products.
The question arises, “How much free oil can I feed to my horse each day”? You need a “carrier” of some sort such as beet pulp, rolled cereal, wheat bran or a coarse mix since horses are not keen on consuming oil by itself. I personally would prefer to “top dress” a coarse mix which will absorb the oil and remain palatable. A 500kg horse will be able to consume up to ~500g or ~450ml oil daily over three feeds but it is important to allow time for the animal to adapt to oil in its diet. It is common sense to start with a little in the diet gradually working up to the desired quantity over a two to three week period . Horses in extremely hard work can be fed up to 10% of the total dry diet by weight but they must be adapted over a four to six week period to enable their metabolic processes to “get in tune”. This would suggest that ~6kg of normal concentrate (~4%fat) would supply ~250g fat so 10% of a 12.5kg daily ration would allow the feeding of 1.25kg fat in total, 1kg coming from added oil. It is important to stress that this amount could only be recommended for a horse in very hard work (top level 3-day eventing, long distance endurance work) that is both digestively and metabolically adapted to this level of oil. It is perfectly possible to purchase manufactured horse feeds which are fat-enriched (up to 10%) so feeding 6kg daily will supply 600g fat which for most horses is sufficient. Small volume, commercially-produced feeds (100g/100kg BW) can contain up to 24% fat so a 500kg horse would receive 120g of fat from such a product. An alternative source of fat is rice bran which contains ~22% fat and is available as an extruded pellet but in the UK it is marketed in a supplemented form so that the fat content is reduced to 18%. It can be fed at up to 1.5kg per day supplying 270g oil to a 500kg horse.
It should be apparent from the foregoing that oil can be supplied in many different formats to horses and from that perspective it is an incredibly versatile ingredient. However, so far we have only really considered dietary fat as an energy source which can be used to increase the energy density of a diet and to reduce reliance on starch sources. Furthermore, it is more than than a performance enhancer. Oil-rich products are very useful for animals that struggle to maintain condition either through old age, compromised gut function (parasite damage) or impaired mouth processing (loss of teeth, etc) because they are both highly digestible and palatable. Another benefit of feeding fat is that coat condition is enhanced gaining a nice glossy look. This was always one of the noticeable benefits of feeding linseed.
It is important not to overlook the fact that feeding oil in place of conventional concentrate will reduce the supply of micronutrients to the horse as well as major minerals and protein. The appropriate course of action rather depends on what other feeds are being supplied. If you are feeding a premium horse feed from a well-known manufacturer then your horse will probably be OK as these feeds contain generous amounts of essential nutrients. If you are less sure of the products you are feeding then take advice which might necessitate using a supplement. Alternatively, buy a commercial, fat-fortified product in which all the necessary additions have been made to achieve a balanced product. Feeding oil is unlikely to bring cost-savings but it could improve your horse’s well being.
In conclusion, oil has many uses in diets for all horses/ponies at all levels of activity. It is very easy to use from the simple “measure and pour” approach to feeding it in an “all-in” diet. At the highest levels of performance it can protect a horse from fatigue so at the end of say an endurance race, it is not the horse that is slowing down the quickest!