Preheat oven to 300 degrees. Combine, in a big bowl, the flours, cornmeal, milk powder, and salt.
In a separate bowl, dissolve yeast in 1/4 cup lukewarm water; let it sit for a few minutes, until it bubbles.
Add the chicken stock to the yeast mixture. Mix well.
Add the liquid to the dry ingredients. Knead about 3 minutes. The dough should be stiff.
Flour a board with cornmeal and roll out the dough to a thickness of 1/4 inch Cut out biscuits with cookie cutters in appropriate shapes, and place on ungreased cookie sheets. Mix the egg and milk and use to brush tops of biscuits (for shine), then bake the biscuits for 45 minutes at 300 degrees.
Turn off the heat and leave biscuits in the oven overnight. This will make the biscuits be bone-hard. Storing Multi Grain Dog Treats
Store these treats in a tightly sealed container. If you are in an area with a lot of humidity you can refrigerate them or even freeze them in zipper bags.
Read more about homemade dog treats including more recipe links