Fibre digestibility of roughage for horses

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Not all hay is the same

Two batches of hay, one rather yellowish and doesn’t smell quite right, the other beautifully green, smelling great of hay and by human standards the ideal produce – but the horses don’t look at it and tend to prefer the – in our eyes – lower quality, yellowish hay.

But what is the difference between different hay samples, apart from the composition of the grasses? What makes one hay tastier than the other? And how can horse owners determine which hay is best for their horse?

No evaluation without laboratory analysis

The laboratory analyses in which the nutritional values and fibre content are determined are of great use in this case. As this can’t be seen by just looking at the hay externally. Laboratories offering hay analysis are to be found Nationwide, they provide precise instructions on how to take and send in the samples so that the results can be easily put into practise.

When such a hay analysis is commissioned, it is usually analysed according to the so-called Weender analysis. The nutritional values analysed include:

• Crude protein (the total protein content)
• Crude fat (the total content of fats and oils)
• Crude ash (the total content of mineral components) and
• Crude fibre (all non-water-soluble carbohydrates, i.e. essentially plant fibres)

Sugar content – the lower the better

When analysing hay for horses, sugar and fructan are also taken into account and listed under combined “total sugar”. As sugar is absorbed in the small intestine and directly increases blood sugar, but fructan is fermented in the large intestine and does not enter the bloodstream as sugar, it is important to differentiate between the two for a qualitative assessment.

The sugar content (not total sugar) in hay should always be below 10% for horses, preferably even at only 6%, especially if diseases such as laminitis, EMS, insulin resistance, etc. are present. The fructan content plays a subordinate role in hay, as the weather conditions at hay harvest generally determine low fructan levels.

Protein – not too much, not too little

The optimum protein content in horse hay is between 6% and 9%. If the crude protein content is below this, protein should be supplemented, e.g. in the form of lucerne or sainfoin. If it is higher, the hay is suitable for sport horses with their increased protein requirements but can lead to obesity (EMS) in heavier breeds and leisure horses.

Where does the horse’s energy come from?

The actual energy supplier in hay for horses is the fibre. Fibre is digested exclusively by the microorganisms in the large intestine and is made up of different cell wall components that are digestible. These cell wall components are hemicelluloses and (water-insoluble) pectins (both quite easily digestible), cellulose (less digestible) and lignin (indigestible for horses).

The larger the plant has grown – and therefore the later it was harvested – the higher the lignin content. The brittle lignin ensures that the stem of the plant remains stable and does not bend, i.e. the crude fibre content increases, but the digestibility decreases as lignin cannot be digested by horses.
In addition, the protein content (crude protein) decreases the older the growth is.

Not all fibres are the same

Unfortunately, the conventional Weender analysis does not look at the different fibre fractions, but only differentiates between crude fibre (cellulose, lignin), nitrogen-free components (NfE, essentially all remaining carbohydrates, i.e. sugar, starch, etc.), crude fat, crude protein and crude ash.

As the digestible fibre content is the decisive criterion for the horse, the Weender analysis was modified in 2004 according to van Soest. A further subdivision was made into non-fibre carbohydrates (NFC, including sugars, starch, fructans and water-soluble pectins), neutral detergent fibre (NDF, all structural carbohydrates such as hemicelluloses, cellulose and lignin), acid detergent fibre (ADF, cellulose and lignin) and acid detergent lignin (ADL, lignin content).

If these fractions are determined, the hemicellulose content can be calculated:
Hemicellulose content = NDF – ADF
The cellulose content can also be calculated: Cellulose content = ADF – ADL

Effect of different fibres

Both lignin and cellulose, which are indigestible or difficult to digest, slow down intestinal peristalsis, i.e. if the horse is prone to impaction colic, it is better to feed a hay with a lower ADF content. If the horse is more prone to diarrhoea, the ADF content should be higher.

This has already been very well researched in rabbits. There, the ideal factor of digestible fibre (DF) to ADF is less than 1.3. If the factor is greater, rabbits get diarrhoea. Unfortunately, data for horses have not been established at this point.

Roughly speaking, the ADF content (cellulose and lignin) should not exceed 45%, as this hay would then have far too little nutritional value. However, such hay can be used to mix with a more nutritious hay to ensure a 24/7 hay supply without consuming too much energy, especially for very overweight (EMS, fat deposits) or good doers.

Ideally, the ADF content of hay for healthy horses should be below 31%. Hay with an NDF content of over 65% is no longer very palatable for horses but can also be mixed with hay that has a higher nutritional value.

The composition of the different fibre fractions is also the reason why horses should not be fed the second cut (“cow hay”). In the second growth, the content of (insoluble) pectins is much higher in relation to cellulose, hemicellulose and lignin, which can lead to diarrhoea, bloat or colic.

Conclusion

Ideal horse hay is therefore a late first cut from a species-rich meadow without high sugar/high performance grasses, which has a high content of cellulose and hemicellulose, a moderate content of lignin and a low content of insoluble pectins.

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