Puppy had pet goat milk, then more cow milk the last two days; today yellow grainy bits on stool — is that a problem?

From the photo the dog has indigestion; the yellow grains on the stool may be curdled milk or undigested corn or similar it sneaked.

Goat milk is more nutritious and digestible than cow milk, so return to pet goat milk and, near one month old, slowly add a little warm-water-softened puppy food.

Feed small, frequent meals to avoid overeating and indigestion.