In part 3, we consider grazing and our options for the good doer.
While it is obvious when we look at a field of lush, rich, green grass that this is unlikely to be suitable for good doers, is the best alternative of very short-cropped grass, or perhaps something in between?
Firstly, it's important to understand that there are a couple of factors here that we are aiming to control, the first being overall quantity and the second being sugar levels and, subsequently, the potential for more calories. When managing the good doer, both factors should be considered.
While we can strive to do the best by our equine friends when it comes to grass intake, it is very rarely completely black and white, although there are some fundamental scientific facts we can base our management on, grey areas still exist, which can muddy the waters. Management must consider not only the facts below but also the individual horse or pony involved.
To understand the reasons behind suitability of different grass lengths, we need to consider where the nutrients are stored within the grass and how we can gauge grass intake.
How much grass does a horse eat?
Research suggests that horses and ponies can eat anywhere between 1.5 - 5.2% dry matter of their body weight per day. As a rough guide, using an average of 3% body weight, a 500kg horse could consume 15kg dry matter of grass in a 24-hour period (on good grass), this is just over 0.6kg per hour. This highlights the very real danger of horses consuming excess calories from grass alone. As a general rule, grass will always provide more nutrients than hay or haylage, so, if the grass is good, the horse's energy demands will likely be partially, if not fully, satisfied (or exceeded) by what he grazes each day.
During the process of photosynthesis, grass creates sugar (sucrose, glucose and fructose), required for growth, and any excess is converted into storage carbohydrates. This sugar can be referred to in a number of ways: one being non-structural carbohydrates (NSC), which is the simple sugars, fructan and a starch fraction of the plant. A term more commonly used in pasture analysis is the term water-soluble carbohydrate (WSC), which encompasses simple sugars and fructans.
UK grass species store excess sugar (produced by photosynthesis) as fructan, while those adapted to more tropical climes store the majority as starch. UK grass species must have the genetic potential to produce high levels of WSC in order to be productive throughout a long grazing season and a cold winter.
When it comes to where sugars are stored, WSCs are generally more abundant in the stem and leaf sheaths than in the blades of grass; levels tending to increase with plant maturity, peaking during flowering and thereafter declining. Over 30% of fructans can occur in the tops of mature plants, especially at flowering (going to head), but levels remain lower if the plant is not allowed to head.
Unsurprisingly, we notice a preference in grazing behaviour that can be linked to sugar storage, selection for grazing being closely linked with WSC content, making reducing WSC intake arguably even more challenging!
In some conditions, WSC levels in the grass can reach up to 50% (dry matter)! This is significantly more than grass hay or haylage which can reach ~20%. Knowing when these sugar levels are likely to be at their peak may help to inform better management for good doers and those prone to problems such as laminitis.
While these figures can sound scarily high, it is important to remember that while undesirable for some, sugar is by no means unnatural for horses. In fact, many working horses of healthy body conditions, tolerate sugar well. However, for those requiring a low sugar and ultimately low-calorie diet, management of grazing is essential, although it is important to note that a completely sugar-free diet is an almost impossible goal. The best that can be achieved is minimising sugar intake from forage (grass, hay, haylage), typically the largest contributor of sugar in the diet.
Sugar levels can vary between seasons. In the UK, there is increased potential for a rise in horses' WSC intake during spring when soil temperatures reach 5°C, and again in the autumn. While there is an increase in the level of WSC during this period, the potential for increased intake is more likely linked to an increased potential intake of grass overall. When considering WSC levels, while certain species can accumulate more than others and certain times of year may see a peak in level, WSC concentrations are more closely associated with environmental conditions.
What impacts the WSC level in grass?
Many factors influence the level of WSCs in grass, and the same grass pasture can vary from year to year and even at different points throughout the day! While there are no absolute guarantees, considering the following factors, which increase WSC levels may help to identify times of greatest potential intake. It is important to note that a lot of these factors have a common theme running through them – stress. When grass is under stress of any kind, WSC levels accumulate.
- Temperature: Cold nights and bright sunny days. The risk of WSC accumulation increases during spring when the grass is growing, when the night time temperature drops below 5°C, and during the winter months, immediately after a hard frost or when grass is snow-covered. In these conditions, the plant is unable to use the WSCs for growth, which can lead to accumulation. The risk increases further when these colder nights are coupled with bright sunny days.
- Reduced soil fertility
- Water stress, e.g. drought
- Sub-lethal herbicide application
- Presence of heavy metals in soil
- Time of day (afternoon/early evening): when the proper environmental conditions allow, WSC levels will rise during the day (sugars are accumulating as a product of photosynthesis), peaking late afternoon and decreasing once the sun sets. The plant then uses these sugars overnight for growth, and levels tend to be at their lowest first thing in the morning(typically 3 am to 10 am). Where grass has undergone 'stress,' e.g. drought or night frost, this process of converting sugar to fibre cannot occur, meaning the grass may still be high in sugar come the morning.· High WSC accumulating species: e.g. Ryegrasses
- Stage of growth: flower/development
- Light intensity: Sunlight and bright days! High light intensity is thought to increase WSC levels in pasture, low light intensity is thought to do the opposite.
- Over-grazing and under-grazing: Over-grazing and exposing the crown of the grass causes' stress' to the plant resulting in increased WSC levels. However, under-grazing and allowing grass to 'go to head' also results in potential for higher WSC intake.
Management tips for reducing WSC intake:
- Avoid turnout on frosty bright mornings during the winter months or bright days in the spring/autumn where overnight temperatures have dropped below 5°C.
- When daytime temperature rises above 30°C, respiration increases faster than photosynthesis and subsequently WSC content is reduced. As such these periods of increased growth may present opportunities for reduced WSC turnout.
- Turn-out early morning or late evening (bearing in mind exceptions noted above).
- Turn-out on cloudy days or in shady paddocks where there is less photosynthesis, so sugars do not accumulate as quickly. It is for this very reason, that wooded areas (excluding trees which can pose risk such as sycamores and oak) can be very effective turnout areas where calorie/WSC intake is trying to be reduced.
- Don't be too focused on grass species. Cultivating a pasture comprising of low WSC- accumulating grass species is harder than it might seem and even then, environmental conditions and management are likely to have a larger bearing on actual WSC intake. The additional challenge is that lower accumulating WSC species are often associated with lower productivity, so choosing a grass species that is well adapted to the growing area and seeking the right advice on seed mix is crucial. Management practises to minimise WSC intake would still apply if a lower WSC accumulating species is achieved, while avoiding plant stress by enhancing soil fertility and moisture level, will also help.
So what is the problem with short grass?
We know that when grass is under stress it is higher in WSCs. So, where grass is grazed close but importantly not to the point where the grass is permanently damaged, the horse is repeatedly taking the newest growth (which is under stress) and therefore likely to be high in WSCs and ultimately calories (and low in fibre). However, this is less likely to be the case where the area grazed is so small that the horse is grazing faster than the grass is growing, which will result in permanent damage to the sward and ultimately degraded bare pasture.
So is longer grass the answer?
In short, no. While longer, older grass is typically higher in fibre and lower in WSC (providing it has not gone to head), the horse is able to take larger mouthfuls and therefore a much greater quantity overall as compared to the shorter grass. Therefore, it is completely conceivable that the same amount of calories/energy (and WSC) could be consumed, therefore potentially presenting a similar risk. In fact, it could be argued that this type of grazing actually presents more risk in terms of overall calorie consumption due to the likely larger quantity.
So what is the answer?!
It is really down to the individual. We know that turning out for a shorter period of time can lead to compensatory grazing (the horse/pony eating more grass in less time!) and is therefore ineffective, so what are our options?
One option would be to graze close but not to the point of sward damage. This can reduce overall intake through reducing bite size (essentially like a grazing muzzle) BUT this could come at the risk of not meeting minimum fibre requirements and crucially not satisfying the horse's appetite (which is linked to dry matter intake rather than number of calories) – resulting in a hungry horse! Long term grazing in this manner can also compromise dentition (causing excessive wear to the front teeth). If you decide to keep your horses under this management (or have little choice in the matter) ensure that you supplement this with a high fibre (late cut hay/haylage potentially alongside straw, (at a maximum 30% of the forage ration)) to help meet requirements and satisfy appetite.
Another option is to remove grazing from the picture altogether. Arguably the easiest way to control intake, by removing the main factor which is difficult to regulate. You can then pair turnout on a bare or woodchip paddock with a suitable low calorie forage source such as late cut forage, ideally soaked and or steamed.
In both of the above management scenarios, Trickle Nets can be used to increase chew time and mimic grazing.
A grazing muzzle is another alternative and despite not quite conforming to that picturesque idea of ponies grazing naturally in the field, can achieve something close to what we are after – opportunity to burn some calories by promoting movement and a trickle feeding of food through the system enabled through essentially restricting bite size. Be sure to introduce these gradually and adhere to best practise regarding appropriate length of grass for use and maximum duration of wear.
Other methods of restriction such as strip grazing and mixed grazing are available but don't work for all, a lot of these systems still enabling intakes which far exceed requirements of many leisure horses and ponies.
If using any management that incorporates grazing, try and also consider the environmental
conditions and let these inform your day to day management. Also consider compensatory grazing. If grass intake is restricted using a grazing muzzle, for example, which cannot be used for more than 12 hours, the remaining 12 hours will need to be spent in a stable/dry lot to avoid compensatory grazing.
Pasture and/or forage is likely to be the main source of sugar in most horses' diets and while some can tolerate this, others may need their intake restricting whether for specific health concerns or to moderate behaviour or energy levels. Grass pasture is undoubtedly one of the most natural feed sources for horses however it is important to consider how it has changed since the horse's evolution and therefore, should be constantly reassessed as part of the horse's diet.