Keeping calves warm in winter is good for calves and good for the farm. Calves that are not cold stressed are healthier and more productive throughout their lives. If you think about the body condition of dairy calves, they don’t have a lot fat on them. They’re pretty lean with only two to four percent bodyfat. This means they don’t have much in the way of energy reserves to use if they get cold. As temperature decreases, basic maintenance requirements for the calf increase. Calves need more nutrients just to stay warm. Nutrients for growth and health are available only after the maintenance requirements are met. If there is an energy deficit, they have less energy for their immune system which then limits their ability to fight disease and simply grow. All in all, not a good scenario, but one that can be offset by management. Addressing changing nutrient requirements is crucial. The increase in nutrient requirements can sneak up on a farmer because young calves will feel the cold before we do. Calves less than three weeks of age need extra energy to keep warm when temperature is below 59°F. That may not feel all that cold to us but it does to a calf. Calves older than three weeks need extra energy to keep warm when the temperature is below 42°F. Wind and wet conditions mean the calf must work even harder to stay warm, increasing the nutrient requirements further.