Nikita Stowers MSc (Nutrition) BSc (Animal Science) BBS
Equine Nutritionist – Veterinary and Nutritional Integration LTD

We’ve all heard the saying “If it ain’t broke don’t fix it” and this rings very true for our horses diets in general. Equally, as Equine Nutritionists, we so often hear “I didn’t change anything and my horse just started to drop weight, go crazy, their coat went dull…" the list goes on and on - often change happens for our horses without us being aware of it at first.  

As much as we do like to keep things simple when feeding horses, there are definitely times and certain situations when we should review our horses' diet in order to help prevent problems occurring. "An ounce of prevention is worth a pound of cure..." and nutritionally it is so much easier to prevent a problem than help your horse recover from one.

Reviewing your horses diet should go hand in hand with changes. Changes could be changes that happen to your horse - like change of season, the horse's workload increasing, or the horse grazing at a new property - or there could be a change in your horse themselves; like their behaviour, body condition, hoof health or coat condition and colour. 

You should review your horse's nutritional balance any time you are concerned, but here are the top three times when we think it's important to review your horses diet, and why.

The key pasture factors

Most of us in New Zealand are lucky enough to have our horses at pasture all year round, but with this does still come with a few challenges. As Equine Nutritionists, we see a large amount of equine problems occurring as a result of seasonal changes, and the most common are usually associated with changes in the horse's behaviour and weight.

Change of season changes your horse's pasture composition

One of the primary drivers of these changes from a dietary point of view is the change in the composition and nutrient profile of our pasture during the year. The graphs below were taken from New Zealand horse properties over the different seasons in a year. It is important to note that these nutrient values have come from commercial stud farms where pasture quality is very good and may not reflect all horse properties.

Source: Hirst (2011)

You can see that there is huge variation during the year for all nutrients; but this is particularly important for nutrients like Energy, Soluble Carbohydrate (Starch and Sugars) and Protein. 

Lets break this down a little further and look at specific nutrients in detail.

Energy (Calories)

As an example let's say we have a 500 kg horse in light work, receiving 3 kg of hard feed with the rest of their diet made up of pasture and hay throughout the year. That horse is likely to be eating around 10 kg of pasture each day.  His calorie intake from pasture is as follows:

Summer – 90MJ
Autumn – 105MJ
Winter – 115MJ
Early Spring – 125MJ
Late Spring – 117MJ

That is a difference in calories from Summer to Spring of 35 MJ!  That’s equivalent to approximately 3-4 kg of hard feed!  When you think about it like that, it’s no wonder that our horses might be feeling full of themselves in Spring, especially if we don’t adjust the rest of their diet accordingly.  Luckily you can counter this pasture surge by adjusting their hard feed volumes, and sometimes their pasture intake if required.

Soluble Carbohydrate (Starch and Sugars)

Non-structural or soluble carbohydrate is a combination of Starch and Sugars, which in pasture is predominantly made up of Sugar, and this is another key nutrient to think about with changing seasons. Let’s look at the same scenario again but this time for Sugars. The same horse's Sugar (NSC) intake is as follows:

Summer – 500g
Autumn – 1050g
Winter – 1100g
Early Spring – 1200g
Late Spring – 1400g

Again we can see that not only have this horses calories increased significantly from Summer to Late Spring - but so too has their Sugar intake, by 900g per day (almost a kilo).

This can definitely affect a horse's behaviour and if we think about spring, this is often at a time when many of us are bringing our horses back into more regular work after a winter spell, and even if they have been in work throughout winter we are often limited by daylight and weather - so it is like a perfect storm for horses feeling "fizzy", "spooky" or "high energy" - especially if we don’t make diet adjustments to help stabilise their sugar intakes.

In this situation we may need to feed alternative forage sources (soaked hay etc) to bring down the total sugar intake for this horse if he is putting on unnecessary weight, or his behaviour is resembling that of a toddler after too many lollies!

Of course many nutrient levels change throughout the year, and so do mineral and vitamin levels - so as we approach each season it is a good time to reflect on your horse's diet and what changes might be required.

Change of location means new pasture composition

As you can see there is a large amount of variation between different areas on the graphs, so it makes sense that when you move a horse (or buy a new horse – yippee!) from one property to another (or sometimes even within a property if your pastures vary) that this can result in a huge change to their diet - and you may see this result in weight and behaviour changes.

From our own pasture sampling over time for VANI clients, we have established that most horse pastures and hays tested on recreational properties fall within 7 - 10 MJ/kg year round. Within this there are a large variety of NSC values that are likely to play a more important role in your horses health and wellbeing.

Change of Workload or Lifestage

Just like a change of season, a change of workload will affect your horse's nutritional requirements.  As their work increases so does their requirement for energy and protein, as well as other nutrients such as vitamins and minerals. The good news is, for most of us our horses fit within 'Light to Moderate work'. If you are working with racehorses in full work, high level eventers, endurance horses or lactating broodmares they may need more nutrition.  As a guide, you can use the below table to see where your horse fits. 

Every horse's requirements are different, but the requirement for energy (Calories) for a resting 500 kg horse is approximately 72MJ/day.  If they are consuming a good pasture based diet and are turned out 24/7, their energy requirement would normally be met by pasture alone. The most common deficiencies we see for horses that are resting or in light work are in the trace elements: Copper, Zinc, Selenium and Iodine, so you may want to give them a daily 60g scoop of Digestive VM (most horses will eat it out of your hand).

If their pasture is limited or restricted, it is likely that they will also need supplementary forage or another fibre source to meet their requirements. You can use this general rule of thumb to increase energy/calories as their working demands increase as outlined below:

• Light Exercise: 20% increase above the daily digestible energy maintenance requirement. The above 500kg horse's requirement for energy would now be 86MJ
• Moderate Exercise: 40% increase above the daily digestible energy maintenance requirement. The above 500kg horse's requirement for energy would now be 102MJ
• Heavy Exercise: 60% increase above the daily digestible energy maintenance requirement. The above 500kg horse's requirement for energy would now be 115MJ
• Very Heavy Exercise: 90% increase above the daily digestible energy maintenance requirement. The above 500kg horse's requirement for energy would now be 137MJ

Adapted from: National Research Council- Nutritional Requirements of Horses (2007).

Watch for changes in your horse's weight or health

It is likely that changes in season, workload or property will result in changes for your horse.  Often changes within the diet may show themselves as changes in your horses behaviour, their weight, coat or even hoof health. If are horses aren’t receiving a balanced diet and/or we haven’t made appropriate adjustments then we may see some of these changes in our horse.  It is a good idea to think what might have changed in their diet - season, workload, property, life stage, something else?) when trying to fix any problems associated with our horse's diets. 

As we approach spring we may start to see nutritional changes manifest in our horses as extra energy that they are looking to burn, especially if their workload isn’t increasing at the same time as the grass is increasing in energy/calories. 

Even if we don’t notice a difference in their behaviour, we may see changes in their bodyweight which is another tell-tale sign that we should look at reviewing our horses diet. Interestingly, we can see both weight gain and weight loss during times like spring. More often we see weight gain as a result of the increased calories in the spring grass compared to winter, however if the pasture changes have disrupted our horses gut, we can see weight loss as the bugs in our horses gut work hard to adapt to the changes in diet. 

In these situations it can be really beneficial to have some quality gut support like the Poseidon Digestive EQ  supplement to help smooth your horse's transition from winter to spring pasture.

If you are noticing other changes to your horse's coat condition or hoof health, this can also be attributable to diet changes but is often linked to changes in nutrients.

• Copper deficiency is often found in horses with dull coats
• Selenium toxicity may lead to hair falling out or crumbly hooves, or an increased incidence of tying up or delayed recovery after strenuous exercise
• Copper and Zinc deficiency are commonly found in horses with poor hoof and coat health
• If your horse is deficient in Iodine they may present with a lack of energy, dull coat/hair loss, lack of appetite and an intolerance to cold weather.

To ensure you are meeting your horse's requirements all year, the gold standard approach is to have your primary forage (usually your pasture) tested, and then often balance your horses diet with a quality trace mineral and vitamin  supplement like Digestive VM. Feeding the recommended rate of this each day will help ensure you are meeting your horse's nutritional requirements year round.

References:

Hirst, R.L. (2011).  Seasonal variation of pasture quality on commercial equine farms in New Zealand.

National Academic Press: National Research Council (2007).  Nutrient Requirements of Horses.