When do I need to stop grazing the silage fields?

Over-wintering cattle can induce poaching and soil contamination on medium to heavy soils, producing a rough surface and increasing the likelihood of soil contamination when mowing.  Grazing by sheep is beneficial, however, as it removes stemmy and dead grass leading to more digestible silage.Beef cows

Ideally you should remove stock before any spring growth appears.  Failure to remove them by the end of January will reduce 1st cut yields and also increase the risk of contamination with manure.  If you do intend to spring graze you should get the stock off by the end of March.