by Dr Carol Michael; PhD
Traditionally spring and the autumn with its spurt of lush grasses, have been the most predictable times when incidences of laminitis, caused by sugar overload, are at their highest (45% of all laminitis cases). Recently however farriers are reporting a significant increase in the numbers of laminitis due to sugar overload, occurring all year round. This includes more cases of prolonged and chronic laminitis. This month is no exception with the possibility of high sugar levels in grass affected by the frost; with a higher proportion being stored at the base of its stem to protect it from frost damage and ensure survival.
It seems unusual for a naturally occurring, and fairly short lived event, to cause such an episode of a life threatening disease; especially at a time of year when an extra supply of energy ought to be considered a good thing. There also seems to be an ever expanding and complicated set of management systems designed to ensure that vulnerable horses are not exposed to a set of circumstances which may trigger an attack. Perhaps it would be useful to examine the events surrounding and preceding the frosty morning attack.
The term endocrinopathic laminitis is applied to an episode of this type of laminitis and is the final outcome of many horses diagnosed with Equine Metabolic Syndrome and Cushing’s disease. Both of these syndromes are on the increase, equine metabolic syndrome is a consequence of being overweight and as 55% of the UK horse population is now considered to be obese and the figure is set to rise over the next five years this has become a significant management issue.
The problem with horses/ponies affected by metabolic syndrome is that the nutrients they receive are in excess or are of the wrong type to what they require to remain in good health. There are a high number of horses and ponies who require far fewer calories than they receive, with the excess then being stored as adipose tissue. The main problem is the amount of glucose/sugar which when ingested must be cleared from the blood as soon as possible. Glucose is toxic and will destroy vital organs including the brain, if allowed to linger, therefore the body has a strict policy on glucose control and it is either used or stored as quickly as possible by a transport system (GLUT 4) under the signalling of the hormone insulin. Continuously high levels of insulin in the blood stream when suddenly topped up by a single incidence of sugar overload (frosty grass) and the consequential response of a fresh release of insulin will cause a laminitic attack, though the initial problem is not the frosty grass but the abnormally high circulating levels of insulin.
The UK horse population has a high number of native breeds and cross breeds as well as breeds such as Arabs which have been bred to survive in the harshest of environments, this is achieved as their endocrine signalling system transmits a different set of information about how to survive and live than does say the endocrine system of a thoroughbred racehorse.
To achieve this homeostasis the endocrine system will relay a whole series of messages about food consumption and storage, energy transmission, suppression or increase of appetite, depression of energy expenditure, coat growth, hair thickness and the time to shed the excess hair. Part of this system is circadian in nature (around a 24hour period) and relies largely upon light, but part of the system relies on seasonal temperatures and nutrient availability.
The problem with modern horses/ponies affected by metabolic syndrome is that the nutrients they receive are in excess of the nutrients they require and this is compounded by the fact that horses are no longer expected to, travel long distances in search of food, cope with extreme or variable temperatures, or grow thick winter coats and shed them at least four times throughout the four seasons of the year.
Thirty years ago most ponies and many horses were roughed off at the end of the school holidays, turned out at grass to grow a thick polar bear like coat, which occasionally had the mud brushed off (a job that could take up most of the day) for a weekend ride or days hunting, and then come in around the beginning of March looking ‘ribby’ for the spring before putting the weight back on through the summer in a natural yo-yo dieting fashion.
Winter coat growth, hair loss and shedding use a metabolic energy (AKT) pathway which involves both insulin and glucose, this means lowering circulating levels of plasma insulin and use of an excess store of energy. Long periods in the stables during the winter/autumn/early summer months will deprive them of the ability to use up this excess glucose and fat storage.
The increased problem of a horse with equine metabolic syndrome is that the fat deposits of adipose tissue contain an independent endocrine signalling system with at least four hormones governing weight loss, energy output and weight control.
Most importantly; homeostasis of weight maintenance and appetite is governed by a balanced set of signals given out both by the adipose tissue and the gastrointestinal tract. In obese horses with large adipose deposits particularly in the neck shoulders and tail area there will be an increased volume of adipose hormones released, which easily outbalance the hormones released from the gut and the vital homeostasis of appetite and weight control is compromised and further weight gain is the result.
As well as hormones of weight control and appetite, adipose tissue also releases a whole series of inflammatory chemicals which put the physiology of the horse into a pro inflammatory state, disrupt the normal circulation of the foot and together with circulating insulin play a major part in the onset of many disease states including laminitis.
Therefore the most important goal is to control adipose tissue gain in order to limit the abnormal and high volumes of signalling hormones that disrupt appetite, influence weight gain, circulation and gastrointestinal function, raise circulating insulin levels and eventually result in an episode of laminitis.
Obviously it is impossible for the majority of many horse owners to go back to rugless winter turn out as a method of adipose tissue control and this is why we as a company in conjunction with three leading bioscience universities are actively involved in the development of compounds from native plant species to diminish adipose tissue and its detrimental effects on the health and well being of the horse.
Dr. Carol Michael PhD
For further technical support and information regarding coming trials contact: www.freestepsuperfix.co.uk