Lameness in sheep

Originally from: Hilary Peters
                        
Could I be right in connecting lameness with the nitrates that go on the land? The sheep in the field I look out on here (all 500 of them) have become increasingly lame since they arrived. This is not a foot complaint, but joints. It seems so common nowadays that no one remarks on it, but this is a recent (ie. in the last 50 years) phenomenon. Am I alone in connecting it with the balance of nitrogen and phosphorus?