After the fawn is about five days old, offer it some grain as soon as it finishes the milk replacement. Put your finger into the fawn's mouth. It will usually suck your finger, getting the grain at the same time. Do this until it gets used to the taste and texture of the grain and eats grain by itself. Don't force it.
Some fawns take to grain right away.
Others just aren't interested for a while. During the first few weeks of life, use a commercially available feed prepared for young calves. Purina's Nursing Chow and Calf Manna are two examples of the many brands on the market that can be successfully used at this stage of the fawn's life. Commercial feeds such as Wod-Lyn Feeds or a feed specifically formulated for reindeer from Alaska Mill and Feed meet these requirements. Check with your local feed supplier for a ration that meets these nutritional requirements.