scouring

I have two bucks that seem to be scouring, tails black and gummed up, went to get fecal sample to take to vet, and one ran off and dropped a big chunk, so I walked over and picked it up, but it looked normal. Why would his (their) backsides be all tarry if they're having normal movements? Still...

I have a doe fawn that seems to be scouring. She is very healthy overall. Feeding 3 cups red cap milk, + 1/2 cup save-a-kid milk replacer + 1 tsp probiotics,+ colostrum . Feeding 2-4 ounces 5 times / day. have a second fawn just started feeding, no scours yet, but if it is the milk mix...