I had this with my current litter. They had good solid stools from birth and on day 2 started with loose watery stools.
A soft stool initially that is mustard colored and looks like a bit of milk curd is normal from the mothers milk. However my pups started to get very watery. Stool samples on such young pups will not show anything according to my vet. They also would not be born with coccidia or giardia; that is something they would pick up in the yard. My pups are raised in my home and don’t go outside till about 4 1/2 weeks of age.
I contacted www.Lambertvetsupply.com (recommended to me by a breeder friend) and spoke with Shanon and the vet on staff.
Bene-Bac was recommended. This is a probiotic for new borns and other age pups.
I followed the dosage advice of the vet at 1/2 mg per pup 2x /day for 3-5 days, as opposed to the dosage on the syringe because I had this issue going on for about 4-5 days already. Once I had solid stools continue for 1 day.
In 4 days they were solid and have been ever since. They are now 4 weeks old.
I have also started them on puppy food/blended with baby rice cereal. I feed Orijen and it is not uncommon to get loose stools when you introduce food, especially a high protein high fat formula. I started at 1/4 cup per pup and they have had good solid stools. I attribute this to the Bene-Bac.