The minimum amount is 2 quarts immediately after birth. Colostrum quality should be checked with a colostrometer to determine its specific gravity which is related to antibody levels. Some veterinarians and nutritionists recommend one gallon (large-breed calf) to be fed immediately after birth to get higher levels of immunoglobulins in the blood. Most calves will not suck or consume a gallon, so an esophageal feeder may be required to get this level of liquid in the calf. If the calf is not hungry at the next feeding, do not force another 2 quarts.
Be sure to keep quality frozen colostrum on hand for those times when a dam's colostrum is inadequate. Be sure to thaw it slowly. Check the resources available under dairy calf and heifer management in the DAIReXNET Web site for more details.
Source: J.W. Schroeder, North Dakota State University Dairy Extension