16/09/2022
Re shared from Carole Huges from Equi biome
Energy metabolism is so finely tuned in our native ponies and cross breeds, do we underestimate the small changes and additions to the diets which may trigger energy/metabolic dysregulation? Why do some horses need to have a poor diet through the winter months? Are we able even to see this as a normal event? Or have our modern management systems created a complete energy crisis of calorie excess when for some horses their metabolic system is totally geared to a calorie deficit?
Energy metabolism is complex but let’s start by looking at leptin…….
‘Leptin is a hormone released by fat cells which in normal horses turns off appetite. However, IR horses are leptin resistant and have elevated levels of this hormone’ quote from E. Kellon.
Leptin is released from adipose tissue and is part of the process of energy and appetite regulation. More fat means more leptin, there is no defined point at which raised leptin levels then become leptin resistance, though it is speculated that high circulating levels of triglycerides are the trigger for this resistance.
In native horses feeding in a wild environment, starvation would be a much more common event than an unrestricted number of calories, wild horses are often faced with a long period of low-calorie intake. For these reasons, any system regulating feeding and body weight would need to be biased toward the acquisition and retention of calories. Good doers are horses with a very finely tuned survival system biased towards acquiring calories, our breed societies have ensured that our native breeds have hung onto this important genetic trait.
Metabolism is a regulatory system that must have some adaption capabilities to cope with sometimes harsh environmental conditions including drops in temperature. A wild horse in January would have a system that could indicate and transmit information concerning fat reserves, they would also need a strong starvation signalling system indicating their calorie reserve, enabling them to stop all other behaviours and jobs other than those which sent them in search of food and to conserve energy.
Leptin appears to have all these characteristics and appears in many parts of the brain in a regulatory capacity, leptin influences many important decisions relating to survival meaning there must be a self-regulating cut-off mechanism to indicate dysregulation, thought to be the high levels of triglyceride. Triglycerides are the signal to say something is going wrong!!
Triglyceride is a transporter of leptin into the brain, but it is available only in relatively small amounts in nature and then only alongside more complex lipids.
Where do triglycerides come from?
Plants contain complex lipids with few triglycerides, processed food pellets/mixes and extruded grains contain few complex lipids and high amounts of triglycerides (high triglycerides are also an indication of EMS). Complex lipids are contained in the seeds and pollen of grass and plants, examples are omega-3 polyunsaturated fatty acids, phospholipids, inositol lipids and second messenger lipids these are responsible for building healthy membranes, and central nervous system function, they are also responsible for the transport of leptin across the blood-brain barrier and for building the barriers (rafts) between brain compartments. Triglycerides are purely a source of energy. The adipocyte or fat cell is designed for continuous synthesis and breakdown of triglycerides, high intake without high exercise means high circulating levels which would certainly trigger a response from a finely tuned survival mechanism.
Lipids contained in processed oils/foods such as pellets and coarse mixes will produce higher levels of circulating triglycerides than complex lipids from plants. High circulating triglycerides are a symptom of EMS. Beware of including any type of oil as part of the daily ration to any horse which has EMS, is overweight or is doing little or no exercise. Oil is great for short periods but shouldn’t be included or seen to be a normal part of the ration for any horse not involved in extreme exercise, needing an extra energy supply. Avoid over-processed and extruded grains, pelleted feed, and coarse mixes.
Take home message, all native breeds (except the old and infirm) should be allowed to experience a period of being cold, wet and hungry, they are totally geared to cope with this. Better than a lifetime of metabolic dysfunction but understandably difficult to do!
