If the calf does not appear hungry and is alert, we assume it is nursing. Continue to monitor the calf closely to see if he is nursing from the mother. If not, and the calf won't take a bottle, you could purchase an esophageal tube feeder and force-feed the calf some milk.

Assuming the calf received its colostrum in a timely fashion, this may be a case of passive eating behavior. Since hunger has not driven the calf to drink yet, someone will have to spend time teaching the calf to accept the bottle. This will require straddling the calf (or using a halter to secure the calf) and introducing the nipple to the mouth. Wiggle it around, get some milk in the mouth, etc., and don't lose patience. You may have to refrain for an hour and try again. Best results are when using milk, not replacer, at this juncture and when the milk is warmed near body temperature. In the meantime, tube feeding may be necessary to keep the calf healthy, especially in warm weather. Only a healthy calf will learn to suckle the nipple. Keep clean water accessible and observe if they drink any.

Dave Fischer, University of Illinois Dairy Educator - Illini DairyNET
J.W. Schroeder, North Dakota State University Dairy Extension