This glossary explains the words you will most often see on horse feed and supplement labels, in feeding advice and in our own articles. Definitions are deliberately short and plain. Where a subject needs more explanation, we link to the relevant guide. Terms are grouped by their first letter.
A
Acidosis (hindgut acidosis)
A fall in the pH of the hindgut, usually when large amounts of starch or sugar reach the caecum and colon undigested and are rapidly fermented. The resulting acidity can upset the microbial population. It is associated with high-starch diets and sudden feed changes, and is one reason feeding little and often is advised. See our hindgut health pages.
Analytical constituents
The section of a feed or supplement label that declares measured values such as protein, oil, fibre and ash, usually as percentages. Comparing these figures helps you understand what a product contributes to the diet.
B
Bacillus
A group of spore-forming bacteria. Some Bacillus species are used in animal probiotics because their spores tolerate heat and storage better than many other bacteria.
Balancer (feed balancer)
A concentrated, low-intake feed that supplies vitamins, minerals and quality protein to balance a forage-based diet without adding much energy. Balancers are fed in small amounts, often a few hundred grams a day. Our comparison of a feed balancer and a vitamin and mineral supplement explains the difference.
BETA
The British Equestrian Trade Association, the trade body for the UK equestrian industry. It runs the NOPS scheme for feed and supplement manufacturers.
Body condition score
A hands-on method of assessing how much fat a horse is carrying by feeling and looking at areas such as the neck, ribs and hindquarters, then giving a score on a set scale. It is a more useful guide to whether a diet is right than bodyweight alone.
Buffer
An ingredient that helps resist changes in acidity. In gastric supplements, buffers are included to help counter stomach acid. Saliva produced while chewing forage acts as a natural buffer in the stomach.
C
Caecum
A large, blind-ended pouch at the start of the horse's hindgut, between the small intestine and the large colon. It acts as a fermentation chamber where microbes begin breaking down fibre. See hindgut health.
CFU (colony forming units)
A measure of the number of viable microorganisms in a probiotic. Labels may give CFU per gram or per daily serving. CFU figures are most useful when comparing products that contain the same organism. Our guide to equine probiotics explains how to read them.
Chaff
Chopped forage, such as hay, straw or alfalfa, often fed with a bucket feed to slow eating and add fibre. It is also a convenient way to carry a powdered supplement.
Colic
A general term for abdominal pain in horses. It has many causes, ranging from mild gas to life-threatening twists in the gut. Suspected colic always needs a vet. See our article on colic warning signs.
Complementary feed
The legal category for most horse supplements and balancers in the UK. A complementary feed is designed to be fed alongside other feeds, such as forage, rather than as the whole diet.
D
DE (digestible energy)
The amount of energy in a feed that a horse can digest, usually expressed in the UK as megajoules per kilogram (MJ/kg). It helps you compare how much energy different feeds supply.
Dry matter
What is left of a feed once all the water is removed. Feeds with different moisture levels, such as hay and haylage, are compared fairly on a dry matter basis.
Dysbiosis
An imbalance in the population of microbes in the gut. In horses it is often discussed in relation to sudden diet changes, antibiotics, stress and hindgut acidosis.
E
EGUS (equine gastric ulcer syndrome)
An umbrella term for ulceration of the horse's stomach lining. It is divided into equine squamous gastric disease (ESGD), affecting the upper non-glandular area, and equine glandular gastric disease (EGGD), affecting the lower glandular area. Diagnosis requires a vet, usually by gastroscopy. See our guide to gastric supplements.
Electrolytes
Minerals, mainly sodium, potassium and chloride, that are lost in sweat and help regulate fluid balance and muscle function. Horses in hard work or hot weather may need them replaced. See our guide to electrolytes.
Enterococcus faecium
A species of lactic acid bacteria used in some animal probiotics.
ESC (ethanol soluble carbohydrates)
A measure of simple sugars in a feed. It is a subset of water-soluble carbohydrates and is sometimes used, with starch, when assessing feeds for horses prone to laminitis.
F
Fermentation
The process by which gut microbes break down fibre and other carbohydrates that the horse cannot digest itself, producing volatile fatty acids that the horse uses for energy.
FFW (free faecal water)
Liquid passed before, during or after otherwise normal droppings, often leaving the tail and hindquarters soiled. It differs from diarrhoea, where the droppings themselves are loose. See our article on free faecal water in horses.
Fibre
The structural carbohydrate in plants, such as cellulose and hemicellulose, that horses rely on hindgut microbes to ferment. Fibre should form the bulk of a horse's diet.
Forage
Grass, hay, haylage and other fibrous plant feeds that form the foundation of a horse's diet. See our article on how much forage a horse needs.
FOS (fructo-oligosaccharides)
Short chains of fructose sugars used as prebiotics. They are intended to feed beneficial microbes in the gut. See prebiotics and postbiotics.
G
Gut balancer
A supplement designed to support the digestive system, usually the hindgut, often combining live yeast, prebiotics and other ingredients. See our guide to gut balancers.
H
Haylage
Grass cut, partly dried and wrapped or baled at a higher moisture content than hay, so that it ferments and is preserved. It is often less dusty than hay and is widely fed in the UK.
Hindgut
The caecum and the large and small colon, where most fibre fermentation takes place. The hindgut microbial population is the main target of horse probiotics. See hindgut health.
I
Inclusion level
The amount of a particular ingredient in a product, often given per kilogram or per daily serving. Declared inclusion levels make it possible to compare products and judge whether an ingredient is present in a meaningful amount.
L
Lactobacillus
A group of lactic acid bacteria found in the gut and used in some probiotics. Several species once grouped under this name have recently been reclassified, so labels may use newer genus names.
Laminitis
A painful condition affecting the laminae, the tissues that attach the hoof wall to the pedal bone. It is often linked to endocrine disease and to high sugar and starch intake. Suspected laminitis is an emergency and needs a vet straight away.
Live yeast
Living yeast cells, usually Saccharomyces cerevisiae, fed as a probiotic to support the hindgut. Products should name the strain and give the amount, often in CFU per day. See our guide to equine probiotics.
Loading dose
A higher feeding rate recommended for the first few days or weeks of using a supplement, before dropping to a maintenance rate. It affects how quickly a pack is used and should be included when working out cost per day.
M
Microbiome
The whole community of microorganisms, including bacteria, fungi and protozoa, living in a particular part of the body. In horses, the hindgut microbiome is essential for digesting fibre.
MOS (mannan-oligosaccharides)
Carbohydrates derived from yeast cell walls. They are used as prebiotics and are thought to bind certain bacteria in the gut so that they pass through rather than attach to the gut wall. See prebiotics and postbiotics.
N
NOPS (naturally occurring prohibited substances)
Substances banned in competition that can occur naturally in plants or contaminate feed ingredients, such as caffeine or morphine from poppy. The BETA NOPS scheme helps manufacturers reduce the risk of contamination, but it does not guarantee a product is free of them. See travel and competition.
NSC (non-structural carbohydrates)
The sugars and starch in a feed, as opposed to structural fibre. NSC is often quoted for horses prone to laminitis or weight gain, where a low figure is generally preferred.
P
Postbiotic
A preparation of inactivated microorganisms or their components, such as fermentation products or cell wall fragments, used to support health. Yeast culture products are often discussed in this category. See prebiotics and postbiotics.
Prebiotic
A substance, usually a type of fibre or carbohydrate, that is fermented by beneficial gut microbes and helps support them. FOS, MOS and inulin are common examples. See our comparison of probiotics and prebiotics.
Probiotic
Live microorganisms that, when fed in adequate amounts, are intended to benefit the host. In horses these are mainly live yeasts and certain bacteria. See equine probiotics.
S
Saccharomyces cerevisiae
The species of yeast most widely used as a live yeast probiotic in horses. Different strains have been studied, so a named strain on the label is useful.
Starch
A carbohydrate stored in cereal grains such as oats, barley and maize. It is digested mainly in the small intestine, but if too much is fed at once, some reaches the hindgut and can upset fermentation.
Strain
A specific genetic variant within a species of microorganism, usually identified by a code after the species name. Research findings on one strain do not necessarily apply to another.
Synbiotic
A product combining a probiotic and a prebiotic, intended to supply beneficial microbes and the fibre that supports them.
V
Volatile fatty acids (VFAs)
Short-chain fatty acids, mainly acetate, propionate and butyrate, produced when microbes ferment fibre in the hindgut. They are a major source of energy for horses on forage-based diets.
W
WSC (water-soluble carbohydrates)
Sugars and fructans that dissolve in water. WSC is often quoted for hay and grass. Together with starch, it is used to assess how suitable a forage or feed is for horses at risk of laminitis.