Tests highlighting a seasonal fall in blood and/or bulk milk urea with a switch to winter diets must not be used in isolation to determine ration changes to safeguard milk production and cow health.

Changes in urea levels in isolation can, at best, be just one-third of the whole picture, misleading producers into taking action that could further jeopardise cow output and well-being, warns David Whitaker of the University of Edinburgh’s Dairy Herd Health and Productivity Service (DHHPS).

Current sample results at DHHPS’s lab suggest low blood urea, often with low bulk milk urea, is being recorded in herds.

But before making any changes, producers must balance a number of indicators, he says.

These include comparing milk production from calving groups in the herd, change in body condition as well as information from “proper” metabolic profiles and milk returns.

“Don’t act on blood or milk urea levels alone – inspired guesswork won’t help,” he warns.