Dairy producers wean calves at birth or at a few days of age, and with a planned and well-designed feeding and herd health program, get by fine. They feed a milk replacer or whole milk until the calf is old enough to consume feed. Success of these baby calf programs often depends on the amount and quality of colostrum fed to baby calves within the first six hours of life.
In beef cattle systems, there are data where calves have been weaned at 45 days of age, and again with a well-designed feeding and herd health program, the calves will do well. For calves that are that young at weaning, you need to be set up with bunks and watering facilities so that smaller calves have easy access to them.
Rations for these calves need to include high-quality feeds because you are working with an animal that has a high nutrient demand and has a non-functioning rumen. Therefore, low-quality roughages will not be well digested. Diets need to be dust free, and ingredients need to be of similar size so that they can't be sorted by the calf.
