A guide to forage analysis and why it's useful
Dr. Katie Williams Ph.D. M.Sc. (Dist) R Nutr
Analysing forage provides key information about the suitability of the forage for a particular horse and is especially important for horses affected by issues such as laminitis.
Conserved forage is the foundation to a horse’s diet when they are stabled or at times when grazing is sparse; a 500kg horse can consume in the region of 10-12.5kg of dry matter in 24 hours when stabled. As forage makes up such a large part of the diet it is imperative for the individual horse or pony’s needs.
Whatever we put in the bucket, it’s unlikely to make a significant difference if the wrong forage is fed.
The nutritional profile of the forage is even more important for those with health issues such as ulcers or laminitis. The level of water soluble carbohydrate (WSC) in forage is particularly important for the management of those with EMS, PPID or who are at risk of laminitis. The level of WSC in hay directly relates to the level of WSC in grass at the time of cutting. Typically, the level of WSC will be higher in hay cut in the afternoon compared to that cut earlier in the day as the grass will have been photosynthesising during the day and accumulating sugar before it is cut. The level of WSC is also lower on a cloudy compared to a sunny day as photosynthesis is usually greatest on bright, sunny days. The type of grass can also influence the level of WSC but analysis shows that the other environmental factors can often have a greater bearing on the result. Many Timothy hays are high in WSC when made in good conditions and can exceed levels in rye grass forages at times too. There are many factors affecting the levels of WSC in grass and therefore hay, and so it is impossible to reliably predict the sugar level which means carrying out an analytical test is vital.
The way forages are conserved has also changed over the years so now, a more accurate description of many so-called haylages, would be ‘wrapped hay’ as they are often very dry which has meant that little or no fermentation has occurred. This means the levels of acidity are no different to a normal hay which can be seen in table 1. If lactic acid levels are used as a marker of acidity levels, then most of the wrapped forages analysed in the UK are too dry for fermentation to occur and so the level of acidity is no different to hay.
The concern about using a true haylage for horses with ulcers is that the fermentation process used to conserve the forage produces acids and feeding a forage with increased acidity levels would not be helpful in trying to manage EGUS. Clearly this doesn’t apply if the forage hasn’t fermented and so it is another reason analysis can be helpful in determining whether a forage is suitable or not. A pH test is a relatively cost effective test if you want to check the level of acidity in a forage.
Getting a representative sample
Results can only give a good approximation of what is in your forage if a representative sample is taken. It is recommended to take samples from several bales if practically possible and mix them together to make the final sample.
Different Analytical Techniques
NIR Analysis A basic analysis for grass hay, wrapped hay and haylage
This analysis uses Near Infrared Reflectance Spectroscopy (NIR) to determine the chemical composition of the forage by measuring light energy that is reflected by the sample and comparing it to calibrated reference ranges. Large amounts of wet chemistry analysis must be performed to calibrate NIR equipment and for this reason this analysis is best suited to common forages including grass hay, wrapped hay and haylage to produce accurate results.
Wet Chemistry – A gold standard analysis for hay and haylage – the most appropriate option for straw and soaked hay
Wet chemistry is a more appropriate analysis technique to use for soaked hays or forages that don’t contain conserved grass such as cereal straw. Some tests, including WSC, starch and minerals, are only available using wet chemistry. Unlike NIR, wet chemistry is a longer analytical process requiring a larger amount of equipment and chemicals and therefore is more costly.
What are we testing for?
Dry Matter – This gives an indication of how much moisture is in the forage. This value is useful to tell us how well a forage is likely to store and is also important to allow us to calculate how much to feed ‘as fed’ to ensure the horse is supplied with enough forage on a dry matter basis.
Crude Protein – This describes the total amount of protein present in the forage but doesn’t tell us about the quality of the protein in terms of the amino acid profile. Low protein forages may need additional protein in the diet to balance them.
Oil – This describes the total amount of oil present in the forage and is typically low.
Ash – This refers to the mineral content of the forage. The term ash originates from the fact that minerals don’t contain carbon and so don’t burn. They are what is left when the carbon containing nutrients such as carbohydrates are burnt off. The higher the ash value the more minerals the forage contains. Very high levels may indicate soil contamination in the sample.
NDF – Neutral Detergent Fibre - This refers to the fibre content of the hay. It includes the lignin, cellulose and hemi-cellulose which are increasingly more
digestible.
ADF – Acid Detergent Fibre - This is another measure of fibre but measures theless digestible cellulose and lignin. The difference between the NDF and ADF values is the hemicellulose content.
Sugar – The sugar value reported in the basic analysis is an approximation by the Luff Schoorl method extracting sugar in 40% ethanol. This sugar value reports on the simple sugars. If you are trying to establish the suitability of the conserved forage for a laminitis prone individual, we would suggest also doing wet chemistry tests for WSC and starch to calculate the non-structural carbohydrate (NSC) intake.
DE – This is a measure of the digestible energy value of the forage and tells us how much energy or ‘calories’ a forage will supply. For performance horses and those that don’t hold their weight well we are looking for a higher DE and for leisure horses and good do-ers a low DE.
Minerals – The level of minerals in a forage can vary greatly and represent the soil the forage is grown on. Typically, levels of copper, selenium and zinc in UK pasture and therefore conserved forage are low and as such we look to supplement these in the ration. As conserved forage usually forms such a large part of the diet, an excess or deficiency of nutrients in the forage can have a big impact
