A ‘good doer’ is a pony or horse that can survive on fresh air, he is a survival expert, but with our modern management are we providing our good doers with a healthy environment or are we predisposing them to metabolic dysfunction? Good doers possess alternative energy systems to help them survive in harsh environments, every now and again they need a harsh environment to re-establish or balance energy metabolism.
What is a harsh environment?
We may not like to see horses in a field, without a rug, with a hairy coat, winter grass and low grade hay/straw to eat, but is this better for the native pony good doer than to have a life time of EMS, possibly leading to laminitis?
What is a cresty neck?
‘Cresty’ necks are unsightly lumps of fat found on the neck of an overweight or obese horse and there is an awareness amongst vets and horse owners that having a ‘cresty neck’ predisposes it to laminitis. In the diagram below, a horse is said to be predisposed to EMS if it has a score of 3 or above. EMS then predisposes a horse to laminitis.
A brief description of the scores in the diagram as follows-
0 No visual appearance of a crest (tissue apparent above the ligamentum nuchae). No palpable crest.
1 No visual appearance of a crest, but slight filling felt with palpation
2 Noticeable appearance of a crest, but fat deposited fairly evenly from poll to withers. Crest easily cupped in one hand and bent from side to side
3 Crest enlarged and thickened, so fat is deposited more heavily in middle of the neck than towards the poll and withers, giving a mounded appearance. Crest fills the cupped hand and begins losing side to-side flexibility
4 Crest grossly enlarged and thickened, and can no longer be cupped in one hand or easily bent from side to side. Crest may have wrinkles/creases perpendicular to topline
5 Crest is so large it permanently droops to one side
Carter, R. A., Geor, R. J., Staniar, W. B., Cubitt, T. A., & Harris, P. A. (2009). Apparent adiposity assessed by standardised scoring systems and morphometric measurements in horses and ponies. The Veterinary Journal, 179(2), 204-210.
Some breeds are more prone to having a ‘cresty’ neck than others, native breeds such as the Welsh, Connemaras, Highlands and Shetland ponies are among the more susceptible as they require less food with lower sugar/starch than many of the other breeds, they also have a natural leaning towards insulin resistance because they have evolved from an environment where food supplies are often scarce and available nutrients change from season to season.
Susceptible ponies (and cross breeds) are called ‘good doers’ and they possess an insulin-resistant genotype as a survival mechanism which makes them more likely to develop insulin resistance, a good thing as it helps them to survive their native harsh mountain/moorland environment. These ponies naturally have a higher level of insulin secretion and a slower glucose disposal rate which is a positive adaptation for sparse food rations. During the harsh winter conditions when glucose is unavailable or scarce the ‘good doer’ will switch to an alternative energy system to ensure survival and as the available food changes from grass to shrubs/herbage such as gorse, tree bark and marsh grass the metabolism will also switch to a more conservative system of energy use and storage which prevents any ingested glucose from entering the muscle and adipose tissue.
Deprived of glucose the tissues then start to use another energy supply (lipids/triglycerides) allowing the dwindling but precious sources of glucose to support vital organs. ‘Good doers’ have lower insulin sensitivity and higher insulin secretion plus high circulating levels of triglycerides. This tendency towards insulin resistance is a natural efficient adaptation that also involves the ‘pay it forward’ insulin system which exists in the gut. The problems start when the ‘good doer’ clashes with the modern management system and change of environment, and switches to a diet containing too much sugar and starch from hard feed, high-quality hay and grass (perennial rye) designed by modern farming methods as suitable for high milk yielding cattle, with no drop in the quality of nutrients through the winter months. ‘Good doers’ are more predisposed to laminitis but any horse receiving more calories than required for work will store the excess as adipose tissue and fat pads will soon appear as ‘cresty necks’, tail pads, shoulders, sheath etc and has the potential to develop endocrinopathic laminitis.
