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, we hear a lot in the field “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 without us even being aware of it and as much as we like to keep things simple when feeding horses, there are times and situations when we should review our horses diet and this can help prevent problems occurring in the first place.  Reviewing our horses diet goes hand in hand with change.  This could be a change not related to your horse like change of season, workload or property, or it could be due to a change in your horse themselves like their behaviour, condition or coat.  So here we will dive into a few of the times when you may want to review your horses diet and why.

Change of season or property

Most of us in NZ are lucky enough to have our horses at pasture all year round but with this comes a few challenges.  In practice we see a large amount of problems coming about as a result of change of season.  The most common are usually associated with changes in behaviour and weight and one of the primary drivers of this from a dietary point of view is the change in the composition and nutrient profile of our pasture during the year.  The below graphs were taken from New Zealand Horse properties over the different seasons in a year.  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 lets say we have a 500kg horse in light work, receiving 3kg of Hard Feed and the rest made up of pasture and hay throughout the year.  That horse is likely to be eating around 10kg 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 35MJ!  That’s equivalent to approximately 3-4kg 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 by adjusting their hard feed 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 horses 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 has this horses calories increased significantly from Summer to Late Spring but so too has their Sugar intake.  This can definitely affect a horses behaviour and if we think about the time of year that this is happening it 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 full of themselves especially if we don’t make required diet adjustments.  In this situation we may need to feed alternative forage sources 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!

Source: Hirst (2011)

These nutrients are of course not the only ones to change throughout the year and so to do minerals and vitamins so as we approach a new season it is a good time to reflect on your horses diet and what changes might be required.

As you can see there is a large amount of variation between different areas on the above graphs so it is really easy to see how when you move a horse (or buy a new horse – yippee) from one property to another (or sometimes even move 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.  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. 

From our own field sampling at VANI over time we have for example 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.  We will focus on this issue in our next blog “Help my horse needs a low sugar diet what do I do”.

Change of Workload or Lifestage

Just like a change of season, a change of workload will affect your horses nutrient requirements.  As their work increases so too does their requirement for energy, 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 with the exception of Racehorses in full work, High level Eventers, Endurance horses and Lactating Broodmares.  As a guide, you can use the below table to see where your horse fits. 

Every horses requirements are different, but for a 500kg horse that is resting their requirement for Energy (Calories) is approximately 72MJ/day.  If they are consuming a pasture based diet and are turned out 24/7 then their Energy requirement should 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.  If their pasture is restricted then 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 horses requirement for energy would now be 86MJ
• Moderate Exercise: 40% increase above the daily digestible energy maintenance requirement.  The above 500kg horses requirement for energy would now be 102MJ
• Heavy Exercise: 60% increase above the daily digestible energy maintenance requirement.  The above 500kg horses requirement for energy would now be 115MJ
• Very Heavy Exercise: 90% increase ( above the daily digestible energy maintenance requirement.  The above 500kg horses requirement for energy would now be 137MJ

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

Changes in your horse

It is likely that the above 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 considering the above points about season, workload, property and life stage when trying to fix any problems associated with our diets. 

As we approach spring we may start to see this manifest itself within 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 then 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 can often be due to changes in other nutrients such as Copper (deficiency is common in horses with dull coats), Selenium (we can often see hair falling out or crumbly hooves with Selenium toxicity or an increased incidence of tying up or delayed recovery after strenuous exercise). Copper and Zinc deficiency are also common 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 horses 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 supplement.

Poseidon Animal Health have just released the mineral and vitamin supplement Digestive VM in New Zealand, and feeding the recommended rate of this each day will help ensure you are meeting your horse's 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.