Hi there,
Green poo can be a number of things. In light of the introduction of cow's milk, it could be a milk reaction. My DD2 had green mucousy (bloody) stools while I was BF'ing and turned out she had a milk allergy. I had to cut everything out. Have you been able to consume dairy while BF'ing? If so it could just be an initial reaction, getting used to digesting the proteins, or the teething, OR a cold, or ALL of the above.
8 bad diapers does sound excessive though. How is he doing now? Have you cut down or cut out the milk? I don't think that much is quite normal for a reaction to introducing milk, but can certainly be in the range for other issues.
Let me know how it's going. Hope he's feeling better and it was just a cold or teething!
