Evaluating scientific methods and production practices for assessing the nutritional and hygienic quality in haylage for equids

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Bale selection: Bales were assessed from seven farms within Devon and Dorset where haylage is predominantly made for feeding to donkeys.   Individual bales were selected by taking the corners, end and middle which included bales from each layer of the stack.  A record of the way bales were stacked was also made.  A total of 66 bales were sampled. 

Pressure test: To determine how well sealed haylage bales were, a single small core was made on the barrel side of each bale.  A one-way valve was inserted and sealed with a rubber seal over the wrap.  Air was drawn out using a manual plumber’s pump and a needle, attached to a pressure gauge, measured the time taken for pressure to drop 200psi.

Bale coring: Six spatially distinct cores were taken from each bale using a mechanical silage corer.  Samples were immediately sealed in bags ready for transport to the laboratory. Disks of wrap were also retained to determine wrapper set up.

Processing and scanning: Cored samples were broken up and mixed manually and immediately scanned using a NIRs4Farm device before subsampling into vacuum bags for analysis (NIR and wet chemistry) at commercial laboratories.  Samples were analysed for dry matter (DM), water soluble carbohydrates (WSC), crude protein, ash, acid detergent fibre (ADF), neutral detergent fibre (NDF) and pH.


To assess variation in haylage nutritive and hygienic quality across a number of farms producing haylage for donkey consumption.

To determine the suitability of commercial NIR based analyses for the provision of accurate results compared to wet chemistry.


Pressure test: Most bales were well sealed with the majority having an excellent seal (above 5mins or 300s) indicating bale wrap had been applied following ensilaging methodology and that bale wrap integrity had been maintained during storage.  The occasional poor result was associated with visible mechanical damage to the wrap or growth of the fungus Schizophyllum commune.

Wrap layers: Nearly all farms met the recommended target of having at least 6 layers of wrap.  Some farms greatly exceeded this which indicates a waste of wrap and a potential for cost and environmental impact saving.  Some issues with wrapper set up were noted, as shown by the variation in wrap layers within each bale. 

Chemical analysis: A relatively strong relationship was found between increased % dry matter (DM) and increased water soluble carbohydrates (WSC).  WSC levels were very variable with an almost 10 fold range found between bales across the different sites.  Levels of butyric acid (a key indicator of poor fermentation) was low in all haylage samples.

Some discrepancies were found between NIRS predicted and wet chemical analysis particularly for certain analytes.  Whilst predictions for DM were fairly reliable, those for protein and particularly WSC were poor.


Having a means of accurately determining the nutritional content of haylage is important when managing dietary intake for donkeys and other equines.  Whilst NIRS analysis offers an opportunity to provide fast and inexpensive information, relative to wet chemistry, this study has highlighted some significant inaccuracies which could lead to forage outside of target nutritional values being fed, with resultant impacts on donkey health.