We wean our heifer calves when they're at least six weeks old and eating starter well. Most of them are weaned right at six weeks. If they're eating starter well at five weeks, I start diluting their milk replacer. By six weeks, give or take a day, they're getting only water in their bottle. Then I start weaning them from the bottle. The process works very well – our calves have virtually no transition problems and we don't have to listen to bawling calves – until winter comes.
When winter arrives, I turn into a chicken when it comes to weaning calves. I fret about whether it's warm enough to move them out to the hutches, take their calf coats off or start the weaning process. I forget that calves, when well fed and well bedded, are incredibly hardy.
So, I've developed a simple decision making aid for working with the calves: if the chickens are out of the coop, it's warm enough to move calves, take calf coats off and wean calves. (At least the chickens are pulling their weight by contributing to my calf management because their egg production went south with the warm weather.)
The chickens seem to take more into consideration than just the temperature before they decide to venture out – like whether the sun is shining and how windy it is. If the chickens stay put, my calf management tasks wait another day. (I actually saw a couple of the molting chickens shivering the other day.) I figure a couple extra days on milk or a couple extra days wearing a calf coat is better than stressing them out when the weather is brutal.