Every season, farms across the country deal with cows going down around calving, and while there are several contributing factors, one of the most controllable is often overlooked. It comes down to how nitrogen fertiliser has been managed on the paddocks those cows are grazing in the weeks around calving. Pasture that is naturally high in potassium, or that has recently received nitrogen, suppresses magnesium absorption in the rumen. That sets up the classic pre-calving trap: low magnesium, or hypomagnesaemia, often develops alongside low blood calcium, or hypocalcaemia. Keep a close eye on the potassium, calcium and magnesium balance in the diet, and where nitrogen has recently gone on, give the pasture time for potassium levels to settle before grazing.