The nutritional value of grass is related to the ratio of cell contents to cell wall contained within it. When grass is young there are more cell contents compared to cell wall. As grass ages (lengthens), the cell contents decrease and the proportion of cell wall increases. By the time grass is ready to be cut for hay, there is little cell contents left but a lot of cell walls.

Cell contents contain a lot of easily digestible calories, whereas cell walls are the fibrous bits which are lower in calories.

This means that long grass will be lower in calories and more difficult for your horse to digest compared to short young grass, however there will be a lot of it in a field for your horse to eat. Short grass will be higher in calories and easier for your horse to digest, but there will be less of it in the field and this will limit the calories it can provide.

Unfortunately there is no simple answer to the question of which is more suitable for a horse prone to laminitis. A horse with no underlying metabolic disease with a high fat score may do better on long grass if his grass intake is limited by either partitioning the field or using a muzzle, whereas a horse with no underlying metabolic disease who has a perfect fat score of 3 may do well on shorter grass. Remember, the amount we feed our horses should be based on their bodyweight, their fat score and how hard they are working and should be adjusted whenever any changes in these occur.

Dr Teresa Hollands Senior Teaching Fellow in Veterinary Nutrition at University of Surrey

Yes it is perfectly safe, and indeed winter weight loss is perfectly natural for our horses and replicates the normal seasonal weight loss which is seen in wild horses.

A study (1) following wild horses over 8 years, found that they went through a 6% bodyweight change over the year with an 8% loss of bodyweight in the winter which they regained in the summer. This would equate to a 40kg weight loss for a 500kg horse. Those individuals that didn’t lose so much weight (& therefore gradually put on weight over the 8 years of the study) were shown to be at the greatest risk of laminitis.

But it is important to clarify what we mean by weight loss. Weight is the sum of muscle and fat cover (& bones etc.) and I suspect that your vet meant that they’d like to see your horse lose some fat cover.

You can achieve this by riding your horse through the winter, so he would maintain his muscles but use up his extra fat. If you were able to do this, then you might not see much difference in weight. However, if you can’t ride your horse as much in the winter, then he is likely to lose muscle tone and his bum and neck might look weak. It is so very important that you don’t try and maintain the outline of your horse with just food. The extra calories will simply bulk out his body shape with fat…and increased fat will significantly increase his risk of laminitis.

1. Klaus M. Scheibe & Wolf J. Streich (2003) Annual Rhythm of Body Weight in Przewalski Horses (Equus ferus przewalskii), Biological Rhythm Research, 34:4, 383-¬-395

Dr Teresa Hollands Senior Teaching Fellow in Veterinary Nutrition at University of Surrey

Laminitis is not a diagnosis but a clinical sign of hormonal or other disease, so this question cannot be fully answered without finding out what caused the laminitis. The first thing you need to do is get your vet to test your horse to determine what caused the laminitis. PPID and EMS are the most common causes of laminitis. These are both hormonal diseases of horses.

In addition to testing for these diseases your vet can also test your horse’s insulin levels: the results of an insulin test will allow your vet to formulate recommendations about grazing. If your horse has PPID there may be no problem with maintaining a horse at pasture once medical treatment has been initiated. If your horse has EMS, then the insulin test results will determine if it is safe for him to be managed on pasture.

Most grass pasture in the UK has a high sugar content so turnout on grass can be dangerous if this is unlimited and done when the horse’s hormones are out of control. You may need to fence off a small area so that you can manage the grazing and create your own 'bare' paddock, or try the muzzle again. Horses shouldn’t be able to remove muzzles if they are fitted properly so seek advice from the manufacturer if necessary.

The other thing to remember regarding 100% pastured horses is to use the natural seasons to keep your horse as safe as possible - allowing an EMS horse to lose weight over the winter months is vitally important to ensure the weight gain over spring and summer does not cause laminitis.

Professor Catherine McGowan Head of the Equine Division at Liverpool University

The description of this horse indeed sounds suggestive of EMS. In order to diagnose EMS in a laminitic horse or pony there needs to be a combination of findings including evidence of abnormal insulin regulation and evidence of obesity or abnormal fat regulation. Certain breeds such as native types or Warmbloods also increase the suspicion of EMS. In order to investigate the presence of abnormal insulin regulation there are several choices of test that can be used and they differ in their ease of performance and diagnostic power. The most straightforward test is just to measure insulin in a simple blood sample. If high then this suggests an increased laminitis risk, but unfortunately this simple test will not pick up all cases of abnormal insulin regulation.

A greater diagnostic rate will be found when measuring insulin following a test dose of sugar and there are a couple of choices of test in this respect. The “oral glucose test” is considered to be the most sensitive test and likely to give the most accurate results.

Obesity is often defined by the visual appearance of the horse or pony perhaps by using body condition scoring or cresty neck scoring. However, a relatively new blood test that measures a fat-derived hormone known as adiponectin does provide evidence that fat may be interfering with insulin regulation. Normal horses have high adiponectin levels and this improves insulin sensitivity whereas obese horses tend to have much lower levels which promote insulin dysregulation and inflammation.

It is also important to remember that tests for insulin dysregulation, which are central to the diagnosis of EMS, will also be abnormal in PPID cases. Thus, strictly in terms of laboratory diagnosis, a combination of insulin dysregulation + low adiponectin + normal ACTH implies EMS only; a combination of insulin dysregulation + high adiponectin + high ACTH implies PPID; and insulin dysregulation + low adiponectin + high ACTH implies EMS and PPID together.

Professor Andy Durham Partner at Liphook Equine Hospital, Hampshire

Several research studies have shown that the endocrine (hormonal) disorders PPID and EMS are the most common cause of laminitis. For that reason, testing for PPID is often a vital part of a laminitis investigation. Increasing age is the major risk factor for PPID, with the disease affecting one in five horses over the age of 15 years. PPID is often slowly progressive, sometimes taking a period of months or years for obvious clinical signs to become apparent. Therefore, a negative test a few years previously certainly does not rule out a horse developing the disease in the future.

Measurement of the hormone ACTH is the most frequently used test for diagnosing PPID, and while it has high accuracy, it is very rare to have diagnostic test which is 100% perfect. For example, very early or mild cases of PPID may have only a small increase in their ACTH levels, returning a test result which is considered to be negative or borderline for PPID. The accuracy of ACTH testing for PPID is at its highest during the autumn months, so repeat testing at this time of year can be very useful for increasing the chances of detecting PPID. There are other diagnostic tests for PPID, and your vet would be able to recommend whether retesting your horse using a different test could be beneficial in this case.

If your horse has suffered from recurrent episodes of laminitis, or has shown any other clinical signs of PPID, repeating a blood test for PPID is definitely worth doing. Reaching a diagnosis for the underlying cause of the laminitis will allow your vet to provide the most appropriate advice regarding your horse’s management and treatment options where indicated.

Dr Jo Ireland, Veterinary epidemiologist at the Animal Health Trust