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"Can someone tell me the difference between haylage and silage and how they relate to hay?"
Haylage and silage are both products of conserved grass. That is to say, the grass has been cut, harvested and packed into either a large, wedge-shaped clamp or a bale wrapped in plastic. The aim of conservation is to preserve excess grass in the spring/summer so that there is forage in the winter – here both haylage and silage are the same as hay. Where they differ is the method used to conserve them. Hay is obviously grass that has been cut and left to dry and the amount of moisture remaining is very low (~15-10%). The drying process is designed to stop undesirable microbes growing in the hay. Haylage and silage are generally wetter products and their method of conservation is quite different from that of hay. The grass is not allowed to dry out for as long as hay so it is still wet when baled. The aim of packing it in a silage clamp or wrapping it in plastic is to create an environment with no oxygen as quickly as possible. This has the same effect as drying out the grass for hay. By removing as much oxygen as possible, the pH of the forage drops – this helps to stop any undesirable bacteria growing and ‘spoiling’ the forage.
The ultimate difference between haylage and silage is the moisture content at which the grass is harvested and packed/wrapped. This makes haylage somewhat drier than silage (~30 – 35% moisture compared with ~75 – 50% for silage) and also alters slightly the processes that occur while the forage is ensiling – the time it spends packed in the clamp or wrapped in the bale before it’s fed. There can be large differences in the nutrient levels found in silage but these variations are much smaller in haylage.
Expert Answer by: Helen Warren