Metabolic diseases of grazing cattle: from clinical event to production disease.

Abstract Extract The main metabolic diseases of cattle recognised 50 years ago, ketosis, grass tetany (hypomagnesaemia) and milk fever (hypocalcaemia), are even more important today, and how we view them has changed radically. Prior to 1950, the emphasis in New Zealand was on identifying these diseases and defining clinical signs and tests useful for their diagnosis, so that appropriate treatment could be provided. By the 1970s, metabolic diseases were considered to result primarily from a breakdown of an animal's ability to cope with the metabolic demands of high production rather than from inherent defects in it's biochemistry, hence the term production disease' evolved. A further major change has occurred over the last three decades due to recognition, especially in New Zealand, of the subclinical effects that deficiencies of glucose, magnesium and calcium have on milk production and reproduction.