How does pasture cause lamintis?

Fructans and starch are not responsible for most cases of laminitis, Dr Teresa Hollands told delegates at the Laminitis Awareness 2010 seminar.

Most cases of laminitis occur when horses are eating grass. Pasture associated laminitis accounts for 66% of cases occurring in the UK. But what causes the laminitis?

Experiments have shown that giving large meals of starch or fructans can cause laminitis. Large amounts of these carbohydrates suddenly arriving in the horse’s large intestine disrupt the normal population of bacteria in the gut, leading to a cascade of inflammatory and toxic events.

However, Dr Hollands, nutritionist at Dodson and Horrell, explained that this process is unlikely to be involved in the majority of cases of pasture-associated laminitis.

Firstly, grass contains little starch. Of the pasture plants commonly found in the UK, only clover has significant amounts of starch. Grasses store glucose that they can’t use straight away as fructans.

It has been shown that laminitis can be induced by giving a large bolus of fructan  (5g-12.5g fructan/kg body weight).  That’s about 3.75kg fructan for a 500kg horse.

How much fructan would a horse eat when grazing? Grass contains higher levels of fructan during the winter. Mixed pasture might contain 150g fructan/kg dry matter of grass in the winter (compared with 6.6g/kg in the summer). If a 500kg horse eats an amount of grass equivalent to 2.5% of his body weight, (12.5kg), his total intake of fructans would be about 1.9kg.

So the full daily intake falls short of the levels that have been shown to cause laminitis. And what’s more, as horses are “trickle feeders”, that fructan intake is spread out over 24 hours. So even in the winter when the fructan levels in the grass are highest, the horse is only likely to eat something like 50g fructan/hour. In the summer the figure is likely to be about 5g fructan an hour - a thousand times less than the amount needed to cause laminitis.

What’s more, recent work has shown that fructans are fermented in the small intestine, and so are even less likely to reach the hindgut in sufficient quantities to cause food-induced laminitis.

So how does grass cause laminitis? “We need to move away from thinking about individual components of the diet "  Dr Hollands suggested. “In the end it is the calories that are the main risk factor.”

“Grass provides more than enough calories for most horses in light work.”

She explained that recent work with World Horse Welfare and Napier University used alkanes to measure grass intake.  Every day, some horses ate an amount of grass equivalent to 5% of their body weight. Some individuals increased their body weight by 4% a week.

“So you can see that grass easily provides horses with excess calories,” she said “ leading to gradual accumulation of fat. Excess calories over time equals fat. Not all fat is the same.”

She explained that research had shown that some adipose (fat) tissue is metabolically active. The fat cells (adipocytes) release numerous biologically active substances (adipocytokines), which affect glucose and fat metabolism. When present in excess they can lead to insulin resistance, which in turn can result in laminitis.

“The slow insidious eating of excess grass over years is the problem; not the grass they ate today. People get insulin resistance and diabetes because they have been on a bad diet for years, not because they ate a doughnut today!”

What can you do to prevent laminitis associated with insulin resistance?

First you need to reduce the fat. Give thirty minutes exercise daily with a heart rate of 80 beasts per minute. (“Turnout in the paddock is not enough” she says). Accept that the horse or pony will lose weight (fat) over the winter.  Indeed encourage him to do so by using lightweight rugs only - so that he burns fat to keep warm.

Do not starve the horse. Maintain the bulk intake (at 2.5% of body weight) - otherwise he will be prone to developing stereotypies or gastric ulcers. But reduce the calorie intake - soak the hay for 12hours or feed oat or barley straw.

Make sure horses do not get too much grass. Consider using a muzzle; increase the number of horses (and /or cattle and sheep) on the pasture. It’s important to feed a balanced diet.  Make sure the horses receive adequate proteins, minerals and vitamins by feeding a low calorie commercial feed balancer.

The solution is to reduce obesity, ensure nutrition is optimal, and increase exercise.

Monitoring respiratory disease

Researchers at the University of Glasgow have developed  two new non-invasive methods of monitoring respiratory disease in horses.

The number of times a horse coughs provides a good indication of respiratory inflammation - the more inflammation, the more the horse coughs. But it is often not practical, or cost-effective, for someone to physically count the number of times a horse coughs over an extended period.

The research team, led by Professor Sandy Love,  has developed a technique that uses a digital audio recorder attached to the head collar to monitor cough frequency over a long period of time.

In a study to test the value of the technique, the researchers compared audio recordings, each lasting one hour,  with simultaneous video recordings. A total of nine recordings were collected from seven stabled horses .

The  graph of the  audio file could then be examined to identify coughs. Not only was this a rapid process - a  recording lasting one hour could be analysed within three minutes - the technique was also found to be very accurate.

When they compared the audio and video recordings the researchers found that every cough was correctly identified, and no extraneous noises, such as foot stamping,  were mistaken for coughs.
They point out that the speed of the  analysis could be increased further by using  computer software to automate the analysis.

The project also led to the development of a simple device that could be attached to the horse’s head collar to  collect expired moisture. It was used to study the constituents of exhaled breath to see if any could be used as indicators of respiratory inflammation.

The researchers found that the most useful indicator was the pH of the liquid condensed from the expired breath. There was trend toward a reduced pH (acidification) in horses with lower airway inflammation.

The concentration of gases such as carbon monoxide, nitric oxide and ethane was also measured, but the researchers found no correlation between these substances and inflammation in the respiratory tract.

The work was made possible by funding from The Horse Trust . Paul Jepson, Chief Executive and Veterinary Director of The Horse Trust said, “ "We are delighted that the research we have funded has led to new, non-invasive ways of monitoring respiratory inflammation in horses. These techniques could have a major impact on horse welfare by improving the diagnosis and treatment of this common condition.”

Bladder stone laser treatment

Normal equine urine contains many calcium carbonate crystals. Despite that, it is not common for stones (“calculi”) to form in the urinary tract of horses. They are most often seen in the bladder (“urocystoliths”) or urethra (urethroliths”).

It is possible to remove them surgically, which may require general anaesthesia and carry the risk of complications - in particular peritonitis. Other methods include disrupting the calculi with shock waves or laser.

Researchers at the Virginia-Maryland Regional College of Veterinary Medicine and the School of Veterinary Medicine at the University of California, Davis have described a minimally invasive technique using a laser to break up the urinary calculi.

An optical fibre is passed through the biopsy channel of the endoscope. This is used to direct the beam from the laser onto the bladder stone. The procedure can be carried out without the need for epidural or local analgesia.

The surgeon sweeps the fibre across the surface of the stone to produce a crater or groove until eventually a fragment breaks off. This process is repeated as many times as necessary until the remaining pieces of urolith are small enough to pass out through the urethra.

Larger fragments are removed by grasping them with a wire basket passed through the endoscope. Smaller fragments are flushed out.

The technique was successful for removing all uroliths and fragments in five of a series of seven cases. The authors concluded that laser lithotripsy combined with lavage and retrieval of larger fragments using the endoscope was a safe procedure. They suggest that if no progress is made within the first 30 minutes the case will have to be managed by other means.

Read more at Equine Science Update

Equine atypical myopathy - possible cause found

Researchers at the University of Bern, Switzerland, have identified a possible cause for the often fatal disease atypical myopathy. They found evidence to implicate a toxin produced by the bacterium Clostridium sordellii. The toxin is known to cause severe muscle damage in mice.

The researchers examined heart and skeletal muscle samples from horses affected with Atypical Myopathy using transmission electron microscopy. They found that the changes that were present were similar to those found in mice affected by the toxin.

They also used immuno histochemistry staining techniques to show that the lethal toxin of Clostridium sordellii was present in the muscle fibres of affected animals. Antibodies from horses with Equine Atypical Myopathy and antibodies to the lethal toxin of Clostridium sordellii both bound to muscle fibres taken from horses affected with EAM.

In contrast, neither of the antibodies attached to normal horse muscle fibres or to muscle fibres taken from horses with other types of muscle disease.

The scientists concluded that there is evidence that the lethal toxin of Clostridium sordellii plays a role, either as a trigger, or even as a lethal factor, in Atypical Myopathy.

Read more at Equine Science Update.co.uk