Silage has largely replaced hay as the main winter feed for animals in the UK, at a huge cost to the biodiversity of farmland in Wales. Silage seed mixes can be one-year to five-year leys, are typically dominated by highly productive grass cultivars and/or legumes and can produce sufficient biomass to allow three or more silage cuts annually – starting in early-mid May. From a farming perspective, silage is largely favoured over hay because a) it preserves more nutrients per ha as there is less field loss, b) it is less affected by weather damage because the cut biomass does not need to lie in the field drying before storage, c) it is less labour intensive than haymaking and d) because silage is better as an ingredient in mixed rations for livestock. Conversely, a) there can be substantial losses in storage if the silage is mismanaged or b) the silage is not fed-out quickly enough, c) the cost of investing in storage equipment that is not multi-purpose can be high and d) silage is heavy and difficult to move.

Silage fields are becoming increasingly common in the Welsh landscape, replacing not only hay meadows but also areas previously dedicated to producing other fodder crops. This ongoing process of conversion to silage is one of the major threats to biodiversity in the wider countryside of Wales.