1) We only assess fat, only under the skin, when doing a Body Condition Score.
It is easy for the inexperienced owner to confuse fat with muscle, fat with ‘gut-fill’, and fat with build or breed conformation. Feel is as important as appearance. Sometimes it is difficult to give a score, but recognising fat is very helpful, even if you can’t put a number on it.
To help owners recognise fat, I use the palm of the hand over the tuber coxae (the ‘hip bones’) as there is no overlying muscle. The bone is oval with an obvious profile separating top and bottom. If the bottom part feels like skin over bone, yet the top has a soft, thin cover of fat, the horse usually has healthy fat levels. Also, I run fingertips, with light pressure, along the ribs at 3 levels: where the top of the saddle flap would be; the widest part of the ribcage, and slightly lower. The ribs of a healthy horse cause fingertips to move in and out, slightly, along 2 of these lines. A neck crest can be difficult for owners to recognise. I cup the hand over the poll and run it down the crest, to in-front of the wither. Excess fat creates an extra arch on the neck.
2) Body Condition Score parts of the horse, not the whole horse all at once.
It takes practice to BCS correctly and very few horses spread an even layer of fat over their frame. We don’t score the whole horse at once, and we can use half-scores. For example, on the 0 (emaciated) to 5 (obese) scale, a horse can have a score of 3.5 out of 5. The Blue Cross even uses a 5+ category for the super-obese. Under this system, the horse is divided into three parts: forequarters (eg. neck), barrel (eg. ribs), and hindquarters (eg. tuber coxae). Each part is given a score out of 5 and the average is calculated .
Researchers tend to use a 1 to 9 system based on a study by Henneke et al.  and separately score at least 6 areas on the horse’s body: the neck, wither, shoulder, ribs, loins and tail-head. This system is particularly useful for horses with irregular fat coverage. Native breeds are especially prone to fatter necks and tail-heads.
3) Photos can help us see the real situation.
If we see our horses every day the weight can sneak on, or off. Photos can help us be more objective - just as when we look at pictures of ourselves and are shocked at what we see. They are also quick and easy for tracking progress. Take a picture from the side and then directly behind the horse, compare with condition score charts and diagrams , and be honest about what you see.
4) A weigh-bridge is the only reliable way to measure bodyweight.
In common with humans, fat also accumulates inside the horse’s body, around the organs and intestines, where we cannot see or feel it. For every 1kg of external (sub-cutaneous) fat there is another 1kg of internal (visceral) fat. So, as horses become fatter, weigh-tapes become less accurate. They often under-estimate actual weight by 50kg, although as much as 100kg has been observed [Horse Logic, unpublished data]. However, weigh-tapes used with a BCS assessment are more accurate than guessing by eye .
5) Cold blooded breeds naturally cycle between fat and thin during a year.
Where native horses experience harsh winters, it is natural for their bodyweight to fluctuate by 20% over the year [1, 4]. Obesity and insulin resistance result from feeding domestic horses too much over winter, standing them in stables all day, and using rugs too often. Putting PPID aside, the year-round fat cob is more at risk of laminitis than a one that cycles fat-summer/thin-winter. Weight gain is easier in summer (below 30 degC), and loss is easier in winter (below 0 degC), so we can work with the seasons if we plan ahead.
6) Starvation, or high-starch diets, are unnecessary for weight control and potentially dangerous
Abrupt starvation (feeding less than 1.5% ideal bodyweight/day) causes fat stores in the body to be mobilised and enter the bloodstream – where the fat can damage the heart. For safe weight loss, adjust for any over-feeding first. A ‘normal’ appetite for Dry Matter would be 2% of (ideal) bodyweight per day . Then, rather than limit the amount of Dry Matter, choose feeds with fewer
calories per kg and increase chewing time. Long-stem forage requires most chewing  and produces most saliva, which protects against stomach acid and ulcers. Hay takes significantly longer to eat than concentrates – especially if fed in an effective slow-feeding device.
The traditional starch/sugar grain diet is no longer necessary, nor healthy, for weight gain. Swedish racehorses have been fed a hay and oil-based diet successfully over several years . When oil is fed to horses in training, a second metabolic pathway in the muscle fibre is opened up. This is a turbo-boost for stamina. Oil can be safely fed at 1ml per kg bodyweight, with sufficient vitamin E in the diet . Feed quality protein sources above quantity.
8) Most horses don’t work as hard as their riders think they do.
Workload for nutrition is often categorised as: maintenance, light, medium, hard, and very hard. A week’s work for a riding club horse consisting of: 3 schooling sessions, 2 hacks, 1 lunge, plus a competition or lesson at the weekend, equates to no more than ‘light work’ based on heart rate data [Horse Logic, unpublished data]. Especially true if stabled, which reduces energy expenditure. Several hours schooling per day, regular galloping, or hill-work, will possibly increase workload to medium-level (eg. 1* eventing). A forage-based concentrate, fed at the recommended amount for workload, may then help (see below). In healthy horses, ‘light work’ can be sustained easily on a forage-only diet.
9) Only thin horses need more calories.
It may seem very obvious, but one of the saddest things I encounter in consultation is the overweight ‘lazy’ horse given half a scoop of a performance feed. The owner knows they cannot feed the recommended amount - but still
10) Inexplicable problems with weight change could be a result of stress.
Weight gain or loss is not as simple as ‘calories in vs. calories burned’. Most owners realise a horse that runs up and down the fence-line and is constantly anxious is burning off energy, and possibly too distracted to eat properly. But horses with less-obvious types of stress (lack of sleep; chronic pain; lack of company; lack of movement) experience low-grade inflammation. This type of stress may lead to insulin resistance and greater fat deposition  for the same caloric intake than normal horses. If the horse or pony is inexplicably resistant to weight change, make efforts to reduce their stress.
This article cannot cover every eventuality or circumstance and is not a substitute for consultation with a registered independent nutritionist, or vet.
 Blue Cross (2017) Fat horse slim [online] Blue Cross. Available from: https://www.bluecross.org.uk/fat-horse-slim Date accessed: 30/7/18
 Henneke, D. R., Potter, G. D., Kreider, J. L., & Yeates, B. F. (1983). A scoring system for comparing body condition in horses. Equine Vet J, 15, 371.
 Ellis, J. M., & Hollands, T. (2002). Use of height-specific weigh tapes to estimate the bodyweight of horses. The Veterinary Record, 150(20), 632.
 Kuntz, R., Kubalek, C., Ruf, T., Tataruch, F., & Arnold, W. (2006). Seasonal adjustment of energy budget in a large wild mammal, the Przewalski horse (Equus ferus przewalskii) I. Energy intake. Journal of experimental biology, 209(22), 4557-4565.
 National Research Council. (1989). Nutrient requirements of horses (Vol. 6). National Academies Press.
 Elia, J. B., Erb, H. N., & Houpt, K. A. (2010). Motivation for hay: effects of a pelleted diet on behavior and physiology of horses. Physiology & behavior, 101(5), 623-627.
 Ringmark, S., Roepstorff, L., Hedenström, U., Lindholm, A., & Jansson, A. (2017). Reduced training distance and a forage-only diet did not limit race participation in young Standardbred horses. Comparative Exercise Physiology, 13(4), 265-272.
 Lucassen, E. A. (2016). Circadian timekeeping: from basic clock function to implications for health. Department of Molecular Cell Biology, Faculty of Medicine, Leiden University Medical Center (LUMC), Leiden University.