Jennifer Little BSc Hons MSc RNutr,
Equinutrition, Independent Equine Nutritionist

During spring, many horses’ behaviour can appear to revert to that of an overly enthusiastic teenager. There are multiple factors that occur as we head into the year, which can contribute. This article aims to examine some of these factors, their knock-on effects, and measures that can be employed to limit their impact on behaviour. Springtime generates many changes to horses’ management and nutrition. While it could be argued that these changes also occur in reverse during the autumn, in my experience these happen across a shorter time frame in the spring. Possibly due to the fact that most horse owners have no desire to rush into winter. Whereas there are lots of incentives for many owners to want to reach spring at an elevated pace.

Spring changes

As daylight hours increase there is a welcome return to riding on an evening in the light, and for many horses this means an increasing workload. If this change in workload is significant enough, it will increase the level of certain vitamins and minerals required, and the amount of energy (calories) to maintain body condition or performance. In this scenario an increase, change or addition to a horses hard feed maybe be required. The increasing daylight hours also sees the return of grass growth. For many grass will start to replace dried forages such as hay or haylage as the main source of fibre. Depending on grazing and management
practises, spring is the time of year where switching fields, changing to rested fields, the length of turn out time to increases, is more commonly seen.

Not only can the amount of grass available change, but so too can the nutritional content of the grass. Young spring grass can contain higher levels of calories and soluble carbohydrates, or sugars, than winter and even summer grass. Additionally, spring can see weather conditions that include warm days but frosty nights. These conditions can further increase the sugar levels within the grass. This combination of changes to forage, management and sugar intake, explains why spring can be a particularly stressful time for those with sugar sensitive horses, such as those with insulin dysfunction. Even for those without insulin dysfunction these changes can pose a real threat to the health and function of the horse’s hindgut.

Hindgut Health & Function

The horses gut functions to digest fibre and convert it into energy for the horse, as well as producing B vitamins, including biotin. This function relies on a healthy, balanced and established population of bacteria. Unfortunately, the stability of these micro-organisms (sometimes referred to as the gut biome) is easily upset by rapid changes to a horse’s diet.

A change of fibre source, or the choice of field, or amount of turnout time, and even the nutritional content within the grass can threaten the health of the gut biome. Especially if these changes happen too quickly. Changes to the fibre source in a horse’s diet should ideally occur in steps, known as a transition phase, over 2 weeks. If the hard feed portion of the diet also needs to be changed to support body condition or increased workload this should also be done with a transition period over at least 1 week.

This phased switch over allows for the gut biome to adjust and adapt to changes in the diet, preventing the production and build-up of lactic acid within the caecum and colon. Reducing the risk of conditions such as hindgut acidosis or even colic.

Hindgut health and sugar

The hindgut biome is also sensitive to a scenario referred to as ‘carbohydrate overflow’. This occurs when the amount of sugar or starch consumed exceeds the capacity of the foregut to digest and absorb it before it enters the hindgut. Once the sugar and starch ‘over flows’ from the foregut into the hindgut it can trigger a series of unfortunate events. Initially it stimulates the rapid proliferation of one group of bacteria, called Amylolytic bacteria. These intern then produce lactic acid, which if the concentration builds up sufficiently causes the death of the beneficial bacteria, inflammation and cellular damage of the gut wall. This is the process being the condition referred to as called hindgut acidosis.

It is possible for this to occur from rapid, over consumption of grass. But it is far more likely from unsuitable feeding practises regarding the hard feed. In how a hard feed is fed, rather than the choice of hard feed. The horse’s stomach is roughly the size of a rugby ball, and the foregut can physically only digest so much as the feed passes through it. As such, any hard feed should be kept below 2kg per meal. If the current feeds exceed this weight they should be split down across a greater number of smaller meals, fed over the course of a day. A further consideration is the amount of sugar and starch being fed in a single meal. Ideally this should be below the updated guidelines of 1g sugar and starch/kg body weight/meal, so 500g for a 500kg horse, per meal. Again, if the current feeds exceed this level they should either be split down across a greater number of meals or transitioned to a feed that contains
lower sugar and starch levels.

Hindgut Health and Behaviour

Disturbances in the gut biome have been linked with multiple negative consequences. Including negatively impacting on the immune system, appetite, hair and hoof growth, and body condition. Frequently the effect it can have on a horse’s behaviour is less well known among horse owners. The impact on behaviour has been well studied but does still require further investigation. What is known to date is that diets of inappropriate feeding methods, of excessive starch and sugar or rapidly changed can cause a number of affects to their behaviour.

Horses with disturbances to the gut biome have demonstrated elevated flight responses. They have been shown to spook more frequently, and to travel faster and further during a spook. They have also been shown to be less inquisitive and more reluctant to investigate novel objects or interact with people not known to them. These changes in behaviour are particularly relevant during spring and early summer when behaviours can escalate, and also when many young horses are being brought into work with the help of novel people.

Managing hindgut health and behaviour

Negative changes in behaviour can have multiple reasons including pain or injury, badly fitted tack, and inappropriate handling to mention but a few. While these causes should be investigated, supporting the gut biome is a great adjunctive process. This can be achieved by ensuring controlled sugar intake, ensuring any changes to a diet observe a transition phase, that fibre intake is considered first and foremost. An additional support package, particularly during times of change is to supplement the diet with a gut health supplement, which includes the probiotic, Yeast. The supplementation of Yeast has been shown to aid a healthy gut biome, support the biome during times of change and even reduce the impact of sugar variations in grazing.

Maximum Gut Health

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A complementary feed that will help horses maintain a calm and focused temperament when under stressful situations.


A grain free formulation that supports your dog’s microbiome health, wellbeing and immune function.


Read our information on the digestive physiology of the horse, including the stomach and the hindgut.


A selection of the most commonly asked questions from delivery information to the suitability of our products.