Raising calves is difficult and one of the more concerning time periods is weaning the calves from milk to grain and forage. The key to weaning these calves off milk is to do it gradually.  Dr. Coleen Jones with Penn State says the successful transition to a diet of grain and forage requires proper rumen development. Regardless of how much milk you are feeding your calves, they will struggle at weaning if the rumen is not ready. The rumen is the largest of the calf’s 4 stomach compartments and is not functional at birth.  Rumen development begins when calves start eating solid food as these foods enter the rumen. Calves usually begin eating starter grain at about 2 weeks of age so the rumen will be developed by 6 weeks of age because it takes at least 2-3 weeks for bacteria to grow and colonize the rumen.  If this plan is followed, the calves can be weaned off milk at 6 weeks. However, even if weaning is performed later, the same principles apply. Gradual feeding of grain must still be used to develop the rumen effectively since rumen development is a function of diet and not age. 

If the calves are drinking a lot of milk and not eating much grain, their rumen is not ready for weaning and digestive disturbances may occur. A gradual decrease in milk production and a gradual increase in grain allows the rumen to adapt before just switching feeds. Calves on large amounts of milk will start eating large amounts of grain as well then get sick with diarrhea and decreased appetite. To avoid that scenario, start calves on 1/2 pound of grain a day for 4 weeks, then 1 pound per day for 2 weeks, and then 2 pounds per day for 1 week while still on milk. This gradual increase in grain over at least 3 weeks will allow the rumen to develop after starting grain and successfully transition the calves.