Katie Williams M.Sc. (Dist) R Nutr, Technical & Product Development Manager
Whilst there is still much to be learnt about the relationship between obesity and disease risk, it is generally accepted that being overweight predisposes an animal to disease. In the case of the horse, laminitis is one of the most serious repercussions of obesity but it isn’t just horses where levels of obesity are high and appear to be rising. Studies investigating obesity in pets as well as humans are reporting worrying levels of obesity but what is behind this trend?
In the spring of 2021, Dengie carried out an on-line survey about weight management in horses and over 650 people responded. We asked horse owners to tell us how they would describe their horse’s bodyweight and 44% described their horse or pony as overweight which reflects levels found in other studies including the European College of Equine Internal Medicine consensus statement on EMS*. Studies show that owners tend to underestimate their horse’s condition, particularly when compared to a professional’s assessment ** and so we thought it would be interesting to know how confident horse owners felt about their ability to assess their horse’s body condition status.
Half of respondents said they were completely confident that they could tell if their horse was overweight and 46% described themselves as fairly confident. 2% said they weren’t very confident and one person was honest enough to say they had no idea. Obviously a survey doesn’t allow us to explore whether the relatively high levels of confidence were misplaced or not but if horse owners are able to tell if their horses are overweight, something else is contributing to the high levels of obesity.
We asked horse owners to share the issues and challenges they have trying to keep their horses at a healthy weight. Not being able to exercise either because of injury or old age was a significant problem for many. This is an area worthy of further investigation as even very light exercise such as walking in hand may have potential benefits for issues such as insulin dysregulation and that level of exercise may be possible with more horses than is currently thought.
The biggest issue reported though, was trying to feed enough to avoid ulcers without resulting in too much weight piling on. Understandably, horse owners are increasingly worried about ulcers and it is known that long periods with insufficient pasture or forage is a risk factor but how do we find the balance between providing enough but not too much?
Around 20% of horse owners mentioned that they can’t limit access to pasture and a third of respondents said they didn’t want to stable for longer. The use of muzzles was also not an option for about a third of horse owners too, either because they didn’t like the idea of using one or they felt it wasn’t safe to do so with their horse or pony. It is an interesting dilemma; as horse owners we want our horses to be out in the paddock because we feel it is where they should be and yet it can present a risk to our horse’s health. One respondent highlighted this with the comment “the grass is lethal at the moment” and many indicated they find owning a good doer particularly stressful. As a nation of animal lovers, we are rightly appalled when an animal is malnourished or starved but we generally don’t consider letting an animal become obese to be quite as despicable. Perhaps it’s because we can empathise with how hard it is to keep weight off when food is often how we express our love and affection for our family and pets?
If we do limit our horse’s access to grass what do we replace it with? Grass hay or haylage can still be too much for some good doers especially if fed ad lib and so we have to restrict the amount we feed.
Achieving consensus and a clear directive on the minimal dry matter intake for maintaining optimal digestive health has been confused by different studies which can be open to interpretation and differ in the timeframe the advice is recommended for. The work of Dugdale et al (2010) is regularly cited as they restricted intake to 1% of bodyweight in dry matter which achieved significant weight loss without adverse effects on the welfare of the horse. However, the criteria used to measure welfare related to behaviour and the time that ponies spent in three major behavioural categories (eating, resting and play). There is no reference in this study to the incidence of gastric ulcers for example. The study lasted 12 weeks and there have been no studies that investigated the effects of longer-term reductions in forage intake.
The frequency with which ulcers is being diagnosed is increasing and this may account for why the recommendations for minimal dry matter intake tend to increase in more recent studies. Morgan et al (2016) state they initially recommended 1.5% of bodyweight in fresh weight of hay but adjusted if necessary depending on response and Rendle et al (2020) cite 1.5% Dry Matter which is the level most equine nutritionists would work to for the long term management of good doers. The veterinary perspective of some of these studies may be to restrict intake in the acute scenario to deal with significant obesity, hyperinsulinaemia and acute laminitis but this is often getting lost in interpretation and communication. Clarity of communications both within the veterinary profession and to horse owners is an area that can be improved.
The general principle is that the lower calorie forage, the more can be fed which is why straw should not be dismissed. Straw often gets “bad press” in the context of gastric ulcers as one study by researchers in Denmark, found that a horse eating straw as the sole or predominant forage source was 4.5 times more likely to have gastric ulcers. What often gets lost when people read this research is the proportion of straw in the ration. In the UK, straw is rarely fed as the sole forage source to horses and, recognising that straw can be useful as a low-calorie forage source for good doers, a follow up study has been published investigating the safety of feeding 50% wheat straw. The research found no increased risk of ulcers from using 50% straw to replace haylage in the ration.
The recent study by Jansson et al (2021) used 50% wheat straw to replace haylage with no ill effects. The rate of consumption of straw mixed with haylage was slower than when fed haylage alone with the resulting effect being a lower plasma insulin response. Straw has a much lower water soluble carbohydrate (WSC) content than grass forages so a lower insulin response would be expected but when the rate of intake was slowest in the evening, the researchers found no significant increase at all in insulin levels. This suggests that using low WSC forages and slowing the rate of intake are both important strategies in managing horses with insulin dysregulation (ID) or the potential to develop ID due to being overweight or obese.
Some simple calculations show that if straw replaces 1/3 of the weight of an average hay, a reduction in energy intake of 16% is achieved. Obviously replacing half the haylage ration will achieve an even greater reduction. However, long chopped straw isn’t for everyone. If a horse has a history of impaction colic or has poor teeth, long chopped straw is not suitable and its hygienic quality can vary, so sourcing the right quality can be tricky. Some horses won’t eat straw, even if there is nothing else on offer. Whilst it might seem wasteful, mixing straw in with other forages can mean it still serves a purpose as it slows the horse down when eating as they have to sort the straw out from the other forage. The significance of rate of consumption of forages is a key area that requires more research but the results of the Jansson et al (2021) study provide an indication that slowing the rate of intake could have significant benefits for reducing insulinaemic responses.
Monitoring your horse
Spotting if your horse is starting to gain weight early is key to nipping the problem in the bud.
There is so much advice available it can sometimes be overwhelming trying to work out where to start. We’ve tried to simplify the advice so you know what you should be aiming for and how often you should be doing things. Many of you will already be doing more than what the following guide suggests which is great, but the aim is to give everyone a realistic starting point on which to build if time, resources and circumstances allow.
Weigh tape – every 2 weeks
- Use the same weigh tape each time you assess your horse
- Make sure your horse is stood square on a flat surface when taking a measurement
- Use the weigh tape at the same time of day
- Track weight changes on a graph so you can spot changes early
- Weight loss of 0.5-1% of bodyweight weekly is realistic. This equals 2.5-5kgs a week for a 500kg horse or 0.5 to 0.75kgs a day
Fat Score – at least every month – it is likely to take a month for a score to change by half a point on the 5 point scale if a realistic rate of weight loss is achieved
- Choose a scale (0-5 or 1-9)
- Score your horse in the key areas where fat is stored and then calculate an average
- Use a pictorial guide to help you
- Why not work with a friend and score each other’s horses to see how you compare?
- For an average horse it is estimated that to change ½ a condition score (0-5 scale) requires weight losses of 20-30kg.
*Durham et al (2019) Journal of Veterinary Internal Medicine.
** Morrison et al (2017) Journal of Equine Veterinary Medicine
Dugdale et al (2010) Equine Veterinary Journal
Morgan et al (2016) Equine Veterinary Journal
Rendle et al (2020) Vet Times Equine
Jansson et al (2021) Animals