Hindgut Health in Summer
The horses digestive system can be split into the foregut, including the stomach and small intestines and then onto the hindgut, which comprises of the cecum, large colon and the small colon, rectum and anus. The food eaten by the horse is digested differently in these two regions. In the foregut digestion is primarily driven by enzymes, breaking down fats, proteins, and simple carbohydrates such as sugar and starch. However, as the horses digestive system moves from the foregut to the hindgut, it switches from being driven by enzyme to being driven by microbes.
These microbes are populations of different types of bacteria and other micro- organisms called protozoa, collectively these are sometimes referred to as the ‘gut biome’. It is this biome that is responsible for converting fibre from the diet into energy for the horse, by a process of fermentation. Fibre should comprise the largest nutrient in any horses diet, and as such the presence of a healthy population of these micro-organisms is essential for a horses overall health and performance. In fact disruptions to the hindgut biome have been shown cause a disease known as hindgut acidosis. This can result in excessive weight loss, reduced appetite, behavioural changes and even colic and laminitis.
The bacteria and protozoa populations within the hindgut have adapted over time to the current diet. Any rapid changes can cause a disturbance in the gut biome, and if significant enough this can result in lactic acid production, the death of healthy bacteria, and the production of toxins within the hindgut, and also the inflammation and reduced integrity of the gut wall. Winter is often considered the challenging season for the hindgut, and as such unfortunately, the challenges of summer can be easily over looked.
In warmer months with longer daylight hours it can appear to be a much easier task owning horses. In many ways the summer months can also be easier for our horses to, but the summer is not free of challenges for the horses digestive system. Careful consideration of seasonal variations can allow management measures to be put in place to ensure the minimal negative impact on the horses in our care.
As the grass starts growing and the ground dries up it is likely that the horse’s management will change from ‘winter’ management, with limited turn out and high levels of preserved forages such as hay or haylage. To that of ‘summer management’, with longer periods of turn out and the dried forages being replaced with an abundance of available grass. Fibre such as grass, hay or haylage are critical for the digestive and mental health of horses, and should form the largest part of their daily feed ration. The minimum amount of fibre required by a horse is 2% of its body weight per day, this weight is based on a dry matter basis. Due to the high water content of grass the actual weight of grass needed to be eaten is far higher than that of hay or haylage. A 500kg horse would need a minimum10kg fibre (dry matter) per day, but the actual weight would be over 50kg of fresh grass per day.
As such a large portion of the diet changes to forages can cause disruption to hindgut Biome and increase the risk of hindgut acidosis. To minimise the risk of this occurring horses should be introduced to new forages, including rested or new fields in a transition period of two weeks. Rather than just being switched from stabled with dry forages to being turned out, or being switched from one field to another, the new source of forage should be introduced in gradually increasing stages.
Turning horses out onto the ‘new’ grazing for a couple of hours initially and then increasing the duration over two weeks until a full switch over has occurred.
A further challenge of summer is that growing grass is not in its self a consistent fibre source. The growth rates, nutritional value of sugars, fibres, proteins and water content of grass is all impacted by the weather. These changes usually happen
gradually and for horses grazed consistently on the same fields they are normally afforded the time required for their hindgut biome to adapt to these changes. However rapid weather changes such as temperature differences, rainfall or
droughts can challenge the ability of the hindgut biome to adapted fast enough, increasing the risk of hindgut acidosis occurring. Monitoring a horses weight and body condition over the summer months can be an efficient tool for early indications of rapid changes in grass volumes and nutritional content.
It isn’t always the case that summer means a high proportion of grass in a horses diet. In certain climates or horse management systems turnout on grass is simply not possible. For these horses it is important that their dried forages be fed sufficiently and in a manner that prevents periods of four plus hours without any fibre source being available, in order to support the health of the stomach. To ensure hindgut health changes to the dried fibre source, including from one batch of hay or haylage to another, should be done gradually over at least a two week period.
Again this will allow the gut biome to adapt to the new forage and reduce the risk of hindgut biome disturbances.
Competitions/clinics – Summer work load
For many horses summer means an increased work load, and even opportunities to travel away to competitions or clinics. Although these events are usually short in duration ranging from a day to a few weeks, they can result in the need for rapid changes to a horse’s management. Required changes to horse management can negatively impact the gut biome, but with careful consideration and preparation these risks can be limited.
Firstly, the forage and fibre sources should considered. While travelling fibre should be provided in the form of hay nets, and timings of access to these while competing also needs consideration. It is important that periods of 4 hours and above without the ability to eat forage need to be avoided.
For hindgut health it is important that this fibre has been consistently in the horses diet. Therefore using their normal dried forage while away is important. If these horses are out at grass, it can be important that a proportion of this hay or haylage remains in their diet throughout the summer. Then while away the hindgut biome isn’t expected to suddenly adapt to a complete change from grass to dried forage.
Many stay away competition and clinic venues provide hay or haylage as part of their stabling package. To ensure continued hindgut health it is advisable to avoid switching to the provided hay or haylage, and instead to take sufficient from home
to continue feeding the same while away. If space or travel limitations means that this is just not possible, consider how much you can take with you and if you are going to run out before returning home, using this to slowly introduce the new forage, just as you would in a transition or switch over phase.
A further potential hazard for the hindgut around competitions or clinics can be the temptation to add in a new feed to provide extra energy. Again the sudden inclusion of a new feed can directly and negatively impact the hindgut biome, increasing the risk of hindgut acidosis. If additional energy is likely to be required it is more advisable to include this are a proportion of this feed in the everyday diet. Increasing the ability of the hindgut biome to adapt to its presence in an increased proportion more readily.
Additionally many compound feeds formulated for higher workloads can contain increased levels of sugar and starch, as can do straight grains such as oats. Feeding excessive sugar and starch levels can directly cause hindgut acidosis. This is due to sugar and starch intake levels exceeding the digestive capacity of the foregut, which then results in sugars and starches over flowing into the hindgut. Once in the hindgut their presence causes the rapid proliferation of the lactic acid producing bacteria, death of the beneficial bacteria, resulting in hindgut acidosis.
In order to prevent this it is important to avoid meals exceeding 2g sugar and starch/kg/body weight /meal, and in the case of sugar sensitive horses this limit is reduced to 1g sugar and starch/kg bodyweight/meal, and no single feed should exceed 2kg for any horse. Where a bucket feeds exceeds 2kg, or contains too high a level of sugar and starch it should be divided down into a larger number of smaller meals fed throughout the day, till each feed falls below these maximum limits. To prevent sugar and starch overflow into the hindgut it is also important to avoid ‘whole’ or unprocessed grains, as their reduced digestibility (due to the fibrous outer layer) increase the risk of undigested sugars and starches from reaching the hindgut. Feed shouldn’t be used to compensate for insufficient fitness levels.
Water & the Hindgut
Summer poses a further challenge for horses and their hindgut, in the form of hydration. As temperatures rise water expenditure increases. As water passes along the horse’s digestive system it is absorbed into the blood stream via the hindgut. If the amount of water being lost from the body due to higher temperature or increased sweating increases, then amount of water are absorbed out of the gut also increases. If too much water is then removed, it can slow the transition of food through the gut, resulting in hard dry faeces or even a compaction. Ensuring free access to clean water, sufficient fibre levels in the diet and increasing the water content of bucket feeds with the use of Soakable fibres or mashes can all help to ensure sufficient water intake during the hotter season.
Supporting the Hindgut
While summer can seem a less challenging time for owners, it is not without the challenges for horses and their hindgut. Considering and planning for likely changes in the diet, work load and management can mean the impact of these challenges can be limited. But, as some of these challenges are unavoidable it may also be worth considering and investing in a hindgut supportive supplement of pre or pro biotics.
These supplements focus on protecting and supporting the vital bacteria populations within the gut, and assisting them to function well and cope and adapted to changes.