The spring fling!

Dr Michelle Logan takes a look at the issue of ‘grass affected’ horses, and explains what else may be going on during the spring season to cause the crazies

As we emerge from the winter months into spring there are lots of changes: longer days, warmer temperatures and fresh green grass growing at last (which for some has been a long time after the drought followed by winter). The first shows and other horse events have been held when permitted under the Covid-19 rules and regulations. There might be some modifications to the schedules, but we are fortunate we are able to go ahead even on a smaller scale. 

These first gatherings of the season or even the first long hack out can result in reports of horses and ponies behaving differently to normal. Descriptions have to include naughty, lively, excitable, reactive, anxious, spooky and unpredictable! Unfortunately, there seem to be more riders falling off at these first events too. 

We often hear about horses (and some ponies) being ‘grass affected’, but is this actually true? Could the behaviour be just due to a sudden change in routine for both horse and rider when neither are used to it and adapted yet? 

Over the last season or two, due to the initial lockdown and the subsequent Covid-19 restrictions there may well have been a very long gap between horse shows. 

We also need to consider that perhaps it’s just that our horses are suddenly getting more energy than they really need (from fresh pasture) and are also feeling really good now they can enjoy the sun on their back? Perhaps their workload is not matching their energy intake, so your horse has energy to burn? 

Or, as many people think, is there something actually going on in grass to cause this behaviour? If so, what can we do about it so we can continue riding our horses and ponies, and (hopefully) competing them when that is possible?

The evidence

At the moment, it is unfortunately very hard to establish scientifically what is actually going on and prove a definite link that the unruly behaviour is caused by something in the grass. There is no testing that can be done that proves or disproves a ‘grass effect’. 

There so many anecdotal reports of horses being completely different after a flush of grass that it is hard not to believe something is going on, and on the other hand, there are lots and lots of supplements out there that are promoted as helping ‘grass-affected’ horses. 

Usually when there are lots of treatment/management aids on offer, it means that there is not one product that has been shown to work with every individual horse. It is also worth remembering that although licensed veterinary products must undergo thorough testing for their claims, supplements do not have to have this testing performed. We will discuss these a bit later on when we look a management of horses in spring. 

What is good about grass? 

Before we look at the theories behind the strange signs associated with spring grass growth, we need to remember what it is about being out at pasture that is good for our horses. A New Zealand study by Hoskin and Gee looked at the value of feeding pasture and some of the findings are below:

A horse or pony out at pasture, given free choice access to graze, will be less prone to getting colic and gastric (stomach) ulcers. They will have a reduced risk of some nutrition disorders and will have less risk of developing stereotypies (these are repeated actions or habits, such as weaving, crib biting and wind sucking). Horses out at pasture are more able to show natural behaviour and have social interactions. They usually graze for 14-18 hours over a 24-hour period and travel between 10-20km in 24 hours. (Wild horses may travel even further than this). Growth rates of youngsters on pasture, including perennial ryegrass, is as good as growth rates of youngsters in other countries where a combination of grain and pasture/fibre is used. Horses do seem to prefer the youngest, fastest-growing, highest-sugar grass when they select what to eat, and they also like clover. 

When we stable a horse or keep it in a yard, we need to remember we are taking these positives away. On the other hand, horses and ponies out at pasture are more at risk from internal parasites (worms) and may also risk eating a poisonous plant.  

Causes of behavioural issues

There are lots of different theories about spring grass. Again, lots of different theories usually tells us we do not really know what is going on yet! Perhaps it is a combination of all of them: different factors affect different horses, or even something else entirely. Some of the issues to consider include:

1. Energy imbalance

One theory is that it is just too much energy being taken in suddenly without the increase in workload to burn it off. Especially if we consider that some horses are selecting the high sugar grasses, they will certainly get a sudden surge in energy levels.  This might also be true if we are over-feeding certain hard feeds with not enough work. Feeding oats used to have this reputation, with the myth that the horse would be ‘hot’ or fizzy if fed too many oats and was not given enough work. It was never oats that were the problem – it’s the over feeding of energy that can cause issues. 

2. Lack of specific training/recent experience 

At the start of the season it is all new again to most riders and horses. You may not yet be riding-fit – you may not be as secure in the saddle for instance, while the horses have been used to a life of luxury in a paddock chilling with their friends, and now things have all changed! It all takes time for things to settle back into a new routine, and there can be a few upsets while this happens. 

3. Low magnesium

Some owners supplement with magnesium as they believe this helps their horse. However when people talk about low magnesium levels in horses they are not really meaning clinically low levels (like can be seen sometimes in cows on lush spring grass, which is life-threatening and needs urgent treatment) so it is very hard to test for and so difficult to prove an effect with supplementation too (and we have to be careful to keep other things balanced). More research are being done on the positive effects of magnesium for a range of issues, so hopefully we will soon learn more about it. 

4. Toxins

Another theory is that it is due to toxins in the grass, but as scientists have not identified what these toxins are we cannot even begin to test for them, or the effect on the horse. This doesn’t mean they aren’t there – but there is no evidence at present. The only toxin we can easily test for is lolitrem B, which is at least one part of the cause of the condition ryegrass staggers.

5. Bacteria in the gut

Another thought is that the high sugar levels cause a change in the bacteria in the intestines, making it more acidic, and that this causes pain. We definitely get changes in the ‘good’ bacteria in the intestines when we change the diet, and these bacteria are very important in the health of the horse. We are only just finding out all the effects they can have. However, when this acid overload effect was looked at in laminitic ponies, it was found that even with the grass being much higher in sugar than normal in sugar, the ponies would need to eat a very large amount to get a significant acidic change – so it has not been proven yet that this is the cause.

6. Insulin

Another more recent theory is that the high sugar levels in the new grass causes high insulin levels in the blood, which may then somehow lead to different behaviour. Studies in rats have shown that those fed on a Western-type human diet (compared to a normal rat diet) were very much more hyperactive and impulsive. 

A Western diet to a rat could be equivalent to feeding lush grass to a horse, which evolved to have to work for its food (travelling many miles) and to eat rough grass. This research is aimed at looking at hyperactivity and other behavioural problems in children, so there is a long way to go before we know really what is going in with our horses in the spring, but the description of hyperactivity and impulsivity could certainly be applied to some of the horses we know that seem to be reacting rather than thinking and processing. 

Finding a solution

If your horse is having behavioural issues, most importantly always keep yourself safe, and get help from a trainer or instructor. You don’t want to have an accident and don’t want bad habits (either your horse’s or your own) to form while you are sorting our any underlying issues.

After considering all of the theories above, it’s not surprising that some horse owners chose to keep their horses off the grass full-time during the spring, boxing or yarding them instead. 

However, as discussed earlier, being at pasture has lots of benefits for horses and ponies, and very few negatives. In addition, it also may not be practical for a lot of owners to keep their horse off pasture, even if they decided they wanted to try. 

One long-term option if you have your own land would be to sow a grass mix that does not contain the really high sugar grass varieties. There are several mixes available and these are becoming more and more popular for horse owners due to decreased risk of laminitis as well as decreased spring grass effect. Hay has also been made from this type pasture and is extremely popular.  

Another option, rather than avoiding grazing altogether until you have low sugar grass varieties available, is to try to avoid grazing at times when the grass has the highest sugar and starch levels. These are also known as non-structural carbohydrates (NSC) and one main one you will see being discussed is fructans. We do know something about high levels of NSC in grass as it is the same situation to avoid when grazing a horse or pony who is prone to laminitis with equine metabolic syndrome. If you can keep your horse off pasture at certain times and feed plenty of low NSC hay or hay that has been soaked for an hour to reduce the sugar levels then you should see an improvement; it may take a few days for things to settle down so don’t give up. You can feed a low GI vitamin and mineral balancer with this to ensure complete nutrition.

Avoid grazing altogether when it is cool at night and sunny in the daytime. When there is sunshine, photosynthesis will take place in the grass to produce energy but it won’t grow that much if the soil temperature is still cool, so then plant won’t use that energy. Instead, it will store it, resulting in high energy levels in the grass.

If it is warmer overnight, then only graze early in the morning (the grass will grow during the night using up some energy, and it won’t yet have had the sun to make more energy). Avoid grazing in the afternoon and evenings, especially when it is sunny but still quite cool.

Using a grazing muzzle may help for some who will tolerate them, but some horses still work out how to eat quite a lot so you will need to monitor your horse. If a muzzle works for you, your horse or pony will still get the advantages of being at pasture without overeating.

A grazing muzzle can help

As already mentioned, there are quite a lot of supplements designed to help with either the digestive system, toxins, or to supplement, for example, magnesium. It is very difficult to prove anything at the moment, some horse owners find one type works for them, and others find no difference. It doesn’t really matter how these supplements work as long as they don’t do any harm, so if you find one that makes a difference for your horse then keep using it. 

Colic and feed changes

We do have to be careful that by trying to fix one problem we may be at risk for another. Sudden changes in diet can be a risk factor for colic so it is advisable to keep feeding some hay while your horse is out at pasture so you are not completely switching from all grass to all hay. This may also reduce the amount of grass they eat, and provide extra fibre. 

Above all, monitor your horse carefully if you take it off grass and yard or box it. Talk with your veterinarian if you have concerns.

In summary

The behavioural issues we see in spring in some horses can be really frustrating to deal with. For those of you that are already feeding supplements which seem to be helping, then continue (as long as they have no side effects). For those wanting to make some management changes, try avoiding exposure to high sugar pasture first. Ideally, the horse needs to be taken off all grass and fed soaked hay to start with, then you can gradually allow grazing at safe times. For the future, investigate sowing low NSC grass mix to allow pasture grazing with all the benefits. In the meantime, get some help from a trainer.