In doing the research on what to feed Abbey I realised I had forgotten most of my biology lessons from school and couldn’t remember what various ingredients were, nor how they are used by the body.

I did a ‘crib sheet’….here it is:


Amino acids – nitrogen-containing molecules containing an amine group. Most amino acids that a horse needs come from the protein they consume.  The horse breaks the protein down and rebuilds the molecules to make most amino acids and new/more proteins. The amino acids horses can’t make are: arginine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. Lysine is often in short supply in a hay/grass only diet. (See this article)

Ash – the weight of inorganic mineral elements of the feed (e.g. minerals)

Crude fibre – a measure of the indigestible content of a feed. It is thought to underestimate the amount of forage fibre as it doesn’t count all the lignin that will be in the cell walls of forage (see this article).

Crude protein – the approx amount of protein in a feed.  Proteins are essential and are used to build body tissues. The body breaks proteins down into amino acids which it then uses them to repair cells, make enzymes, hormones and blood, for example. There is evidence to suggest to many horses don’t receive enough protein from forage alone. Protein can also be an energy source (the amount of energy they provide can be compared to carbohydrates (sugars), oils are much denser sources of energy).

Digestible Energy – normally measured in MJ/kg. The amount of energy in the feed minus the energy in a horse’s poo.

Fibre –  is made up of complex carbohydrates (sugars) and is broken down in the hindgut. Its fermented by bacteria and protozoa to produce volaile fatty acids.

Oil – oils are 99% fat, they are a dense source of energy (and weight gain!)

Sugar & starch – Sugar and starch are absorbed in the upper intestine

  1. Simple sugars are a one-sugar unit that is readily and rapidly digested in the upper intestine.
  2. Starches are a small group of sugar units connected together that quickly digest and absorb in the upper intestine. (see this article)


A group of organic compounds that cannot be made by the body and are needed for normal growth and general health.

A – for bone and muscle growth, reproduction and healthy skin. Stored in the liver for up to 6 months, doesn’t generally need supplementing.

B – there are a few different ‘B’ vitamins: B1 (thiamine), B2 (riboflavin), niacin, pantothenic acid, B6 (pyroxidine), biotin, B12 (cobalamine), and folacin (folic acid or folate). They are involved in a wide variety of processes including metabolism of carbohydrates, proteins and lipids, red blood cells and DNA.

C – an antioxidant, also involved in the making of collagen, teeth and bones. A horse can make vitamin C from sugar in the liver and doesn’t normally need supplementing.

D – a hormone involved in the absorption of calcium and phosphorous (needed for healthy bones, see below). A horse can make vitamin D if it gets enough UV light.  It’s also present in hay. Doesn’t normally need supplementing.

E – an antioxidant but also used in muscles, the nervous , circulation and immune systems.  Vitamin E is in grass and alfalfa. Doesn’t normally need supplementing.

K –  activates blood coagulation, is made by the bacteria in the large intestine. Don’t need to supplement.


Inorganic compounds that are needed for healthy growth. Some are needed in relatively large amounts – macrominerals, others in relatively small amounts – microminerals.

Calcium (macromineral) – needed for healthy bones, also used by the body for neurotransmission (communications via nerves) and in muscle constriction (see magnesium). Has a relationship with other minerals including phosphorous, potassium and magnesium. Research suggest most horses, especially those with alfalfa or sugar beet in their diet, get plenty of calcium from their forage (UK) without supplementation.

Chloride (macromineral) – like potassium and sodium, a horse will sweat out chloride but a salt lick should provide a horse in normal levels of work with a sufficient balance.

Cobalt (micromineral) – used by bacteria in the hindgut to make vitamin B12

Copper (micromineral)  – used in the elastic connective tissue, in the metabolism of iron and in energy production.  Most horses get the copper they need from forage.

Iodine (micromineral) – used by the horse to make the thyroid hormones, don’t normally need to supplement.

Iron (micromineral) – nearly 70% of iron is found within a horse’s red blood cells. The body reuses iron when the red blood cells dies. Most horses do not need any additional iron to that found in their forage. Alfalfa and sugar beet have particularly high iron contents.  Over supplementation is a concern as iron inhibits the absorption of other minerals (copper and zinc, for example). Read this article for more information.

Magnesium (macromineral) – regulates enzymes, aid oxygen delivery to muscles (see this article).

Manganese (micromineral) – needed for the metabolism of carbohydrates and fats, is in cartilage.

Phosphorous (macromineral) – a key component of the energy units of the body (ADP and ATP), and found in bone, cell membranes, nucleic acids (what DNA is made of). Needs to be balanced in relation to calcium and need to be careful of the source, needs to be low iron.

Potassium (macromineral) – mainly found in muscle cells, potassium regulates water and movement of muscles (every heartbeat relies on potassium). Supplementation is rarely needed as forage is a good source of potassium (only with very heavy sweating and even then, a salt lick should be plenty) . (See this article.)

Selenium (micromineral) – an antioxidant, in conjunction with vitamin E. Also involved in controlling thyroid hormone levels and muscles.  Sometimes needs supplementation, depending upon the levels in forage.

Sodium (macromineral) – A good article here. Sodium has a variety of roles with the horse; in the nervous systems, as a carrier of other substances (glucose, amino acids and other nutrients) across cell membranes and as a regulator of water.

Zinc (micromineral)  – important for healthy bones, skin and hooves, metabolism of carbohydrates and proteins. Present in most forages (more so in fresh grass than in hay) and grains.



Because feed is such a complicated issue, I’ve written a number of blog posts sharing my research and my decision making process: