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The first one is too thin and is not putting on weight despite ample food. The other is overweight and fails to shed pounds, even though its diet has already been carefully rationed.
If you have a horse facing such a problem, you find yourself in a maze of feed supplements, each promising to provide a solution.

The daily amount of nutrients a horse should be fed depends on numerous factors. Initially, it is crucial to assess the nutritional status of the horse.

The first pitfalls emerge here: a fat belly in horses, unlike in humans, does not necessarily involve stored fatty tissue but can simply indicate flatulence or a lack of abdominal muscles.

However, it is also crucial to closely inspect areas typical of fat deposits to determine whether it is indeed fat or just stored water (lymph). This is because fat and lymph have very different causes and, consequently, must be approached distinctly in terms of dietary nutrition.

Body Condition Index

To assess the nutritional status of your horse, you can refer to the Body Condition Index (BCI) designed for horses. The BCI assists you in realistically assessing your horse’s weight and, in contrast to the Body Condition Score (BCS), also distinguishes between muscle, fat, and lymph deposits. By tracking the results over an extended period, you can also observe the progress in your horse’s nutritional status.

Depending on the information you receive or assess visually, you either, in the best case, don’t have to make changes to the feed or you adjust calories or nutrients accordingly.

Keeping an eye on training

The next step is to objectively assess the actual work performance of your horse. Many leisure horses often do not surpass the energy requirements of a horse in maintenance, which solely needs the energy to sustain itself. In fact, light work is defined as 30 minutes of walk, 20 minutes of trot, and 10 minutes of canter daily! That’s quite a lot, and especially for ration calculation and determining the actual additional requirements, this should be assessed very realistically—for the benefit of the horse. It is helpful to ride with a stopwatch for four weeks and maintain a diary to track how much the horse actually works. Even horses affectionately labeled as ‘sport horses’ by their owners often barely meet the maintenance requirements.

Determine the energy requirement

In most cases, horses can fulfill their energy requirements solely from hay or grass. But first, let’s take a closer look at energy requirements in general. Here, a distinction is made between digestible energy (DE), measured in MJ DE, and metabolizable energy (ME), measured in MJ ME. MJ always stands for megajoule as a unit of energy, so it should not be confused with our kilocalories (kcal).

The energy that the body can extract from a feed is known as digestible energy (DE). Put simply, it is calculated from the amount of energy fed into the horse at the front minus the amount of energy that comes out of the horse at the back. The energy actually available to the horse is known as metabolizable energy (ME). The difference between DE and ME arises from the fact that, for example, the microbiome, including bacteria in the large intestine, also consumes a portion of the energy from food. Logically, this energy consumed by the microbiome is not available to the horse as energy, which is why the value for DE is always higher than that for ME.

To calculate the required feed quantity, it is therefore essential to check whether the delivered energy of the feed is specified as DE or ME. The ME is calculated by raising the body mass to the power of 0.75 and then multiplying it by the energy requirement per kg body weight (BW).

To complicate matters, different breeds also exhibit distinct energy requirements. For warmbloods, a maintenance requirement value of 0.52 MJ/kg BW^0.75 is applied. For a 600kg horse, the BW^0.75 would be 121kg, and when multiplied by 0.52 MJ/kg, it results in an energy requirement of 63 MJ ME per day for this horse.

A value of 0.4 MJ/kg BW^0.75 is assumed for ponies, while for thoroughbreds, a value of 0.64 MJ/kg BW^0.75 is considered. Ponies are aptly labeled ‘light feeders’ due to their highly energy-efficient metabolism. In contrast, thoroughbreds are akin to ‘gas guzzlers,’ requiring more energy, particularly during training.

The digestible energy is determined by raising the body mass to the power of 0.75 and then multiplying the result by 0.6 MJ.

Feeding 2kg of hay per 100kg of body mass per day significantly exceeds the maintenance requirement, delivering 7.1 ME and 8.5 DE per kg of hay, based on average values from the 2020 hay harvest (source: LUFA).

Adequate energy is crucial, particularly during periods of physical activity in horses. Even during light work, the energy demand is typically met by hay, especially when horses have hay ad libitum, allowing them to consume additional hay as needed. This is evident in hay consumption, with horses typically consuming 2-3% of their body weight (equivalent to 2-3 kg of hay per 100 kg of body weight).

For light work, the energy requirement can be estimated at metabolisable energy times 1.25, for medium work times 1.5, for demanding work times 1.75, and for heavy or very heavy work, times 2 or even times 2.5.

As the content of digestible or metabolisable energy in hay can vary significantly, conducting a hay analysis is helpful. Conducting a hay analysis should always be the initial step before resorting to supplementary feed for energy, as there could be various reasons why a horse might not fully metabolize the energy present in its hay. If the suspicion that the hay provides insufficient energy is confirmed, it is advisable to adjust the energy content of the ration.

When horses are trained beyond the energy content of their roughage ration, they resort to proteins as a secondary source of energy. If you aim to offer a bit more energy, incorporating lucerne or sainfoin into their diet is a recommended choice, as these forages also supply high-quality protein.
Since not all proteins are created equal, paying attention to the levels of lysine, methionine, and threonine is especially crucial. Hence, opting to feed lucerne or sainfoin is a wise choice.

If horses have access to pasture, protein and metabolizable energy supply is typically ensured without any issues. On average, grass provides approximately 1.7 to 1.8 megajoules of metabolizable energy per kilogram. If the pasture is not time-limited or a muzzle restricts feed intake, and if there is sufficient vegetation available, a 500 kg horse consumes between 40 and 50 kg of grass per day. This daily consumption of 40-50 kg corresponds to approximately 1.5 kg of dry matter feed per 100 kg of body weight, considering the grass’s dry matter content of between 15 and 20%. While grazing, it’s important to consider that the young grass in spring contains significantly more protein than the overgrown grass later in the year.

If the horse’s grass intake is restricted as mentioned earlier, it is crucial to supplement with hay, as the horse requires cellulose and hemicellulose for its primary energy production.
Straw primarily contains lignin, which is beneficial for regulating the horse’s large intestine peristalsis. However, it is not suitable as the sole feed when grass intake is restricted, as lignin is challenging for the horse to digest. Eating excessive amounts of straw in an attempt to meet their energy needs can result in constipation colic for the horses.

The principles that apply to energy and protein content also hold true for minerals and vitamins. As a general rule, there is usually an ample supply of minerals and vitamins, often leading to more oversupply than undersupply. Nevertheless, due to the fluctuating contents of the basic feed, it is advisable to occasionally supplement with a mineral feed to compensate for any deficiencies in the roughage.

The values mentioned above are theoretical calculations for an ‘average horse.’
In practice, it’s crucial to consider factors such as the horse’s age, living conditions, and, most importantly, the individual animal’s feed conversion. The ration should be adjusted accordingly.

That’s why the adage holds true: the eye is the best guide for feeding!