Protein exists as a genuine ‘food’ source consisting of amino-acids (individual proteins) joined in a chain with a nitrogen molecule on each end.  Examples of protein rich foodstuffs are Lucerne (alfalfa), soy-bean, rape-seed, linseed (flaxseed) and other vegetable protein ‘meals’, like peas, beans and lupins.

When this protein is digested in the fore-gut (small intestine) it is broken down into its individual amino acids and nitrogen. These are subsequently reconstituted into the proteins of the various body tissues such as muscle, skin, hair, hooves.   If too much protein is fed, amino acids and nitrogen are floating around which are surplus to requirements.  Then the horses body needs to deal with this by excreting the excess in the urine and manure.

The horse’s diet needs to contain an appropriate level of crude protein with access to essential and limiting amino acids. Protein is critical to good health, however the amount of protein needed is relatively low.

Problems occur when excessive crude protein and non-protein nitrogen(NPN)  is ingested. Horses are not adapted to high nitrogen forage. In the comparatively infertile regions where they live in the wild they would only be exposed in spring. Yet many people tend to think ‘the greener the better’.

In the domestic environment excess nitrogen comes from :

  • Fertilised soils
  • Frequent harrowing of manure
  • Climatic conditions: droughts, frosts, rows of cloudy days, cool night-time temperatures
  • Spring and Autumn pastures
  • Actively growing grass, stressed or over grazed pasture
  • Excessive clover which is a nitrogen-fixer
  • Excessive Plantain which is a nitrogen accumulator
  • Immature grass after a drought-breaking rain

Any one of these, let alone a combination can result in crude protein levels well in excess of 20%. In scientific studies on the subject a crude protein level of 18% is considered ‘high’.

Whilst the organisms of the horses’ microbiome require some nitrogen in order to function optimally it is a delicate balance. Excess nitrogen can act as a ‘fertiliser’ on the hind-gut flora and cause uncontrolled growth that disrupts this delicate balance.

Be mindful of the issues that excess nitrogen in the diet can cause and work to minimise exposing your horse to excesses in his diet. Try to:

  • Avoid fertilising with fertilisers that contain Nitrogen (NPK, Urea, Chicken Manure)
  • Avoid frequent harrowing of manure over the pasture. Occasional harrowing is fine but be mindful that you are spreading nitrogen. By choice horses avoid consuming grass growing on high nitrogen areas where they have dropped their manure. You will see this grass grows dark green due to the high nitrogen content. Grass that is lacking tends to look yellowish.

How does excess protein/nitrogen affect your horse?

Many of the issues we term grass affected are inter-related with excessive protein and nitrogen in the diet.  Along with the problem of excessive potassium creating imbalances within the macro mineral profile required by the horse,  dealing with excessive protein and nitrogen adds to the negative load on the horses natural systems which are not designed to cope with high levels within the diet. 

In particular, when excess protein is available for energy, its processing generates three to six times more heat than that generated from fibre carbohydrates. This can cause the horse to sweat and urinate excessively and he will therefore not perform as well in hot weather.  The process of turning excess dietary protein into energy takes place in the liver and produces nitrogen waste-products (ammonia and urea) which are eventually excreted via both manure and urine. This is what causes the strong ammonia smell when horses are kept in confined spaces and also what causes the urine to ‘burn’ the ground.

By following our feeding protocols you can avoid exposure to excessive protein and nitrogen in the diet.  Feeding mature grasses and good horse hay along with a very simple balanced bucket that avoids nitrogen loading feedstuffs will automatically reduce the likelyhood of too much protein and nitrogen in the diet.   Only feed mirconised linseed at the rates we suggest, this will provide the important omega 3 and 6 fatty acids that the horse needs.  Linseed meal is about 20% crude protein – which is why we stress that it is important not to use this very beneficial feedstuff in larger amounts.


Remember that individual horses have differing requirements. The quality of forage that may be fed to avoid the issues listed on the Health Checklist, including head-shaking or laminitis, will require that attention is paid to supplying just the right amount of quality protein.  This is why we recommend that compromised horses are fed our Premium MVA vitamin, mineral and amino acid supplement along with our other management protocols.