I agree about using the goat's milk w/ water for formula. I also add a little karo to it. I've read that goat's milk has a lower sugar content than canine milk so a little karo helps.
I don't use a commercial milk replacer. I've used Just Born in the past and the pups got constipatiion. Also, with Esbilac, there's a thread in the breeder's forum about the dangers of it. Here's the link if you're interested.
http://www.yorkietalk.com/forums/bre...ment-milk.html
I'm just posting this as general info since you're not on right now and I don't know how the pups are doing or what you're feeding. Also, generally speaking, a hard belly can be gas or constipation. You have to watch it with newborns as their systems are very delicate and easy to upset.