Why mucous in infant stools sometimes accompanied by tiny blood strains. My baby is almost 5 months old. We have switched to goat milk one month ago.

Milk intolerance. How is your child doing on goats milk? Hopefully better. Your child may be cows milk intolerant.
Goat's milk has many. Of the same proteins as cow's milk, so babies can develop an allergy to it. Goat's milk has 1/5th as much vitamin B12 & 1/10th as much Folic Acid as cow's milk. There's 1 mcg of folic acid/8 oz.Of goat's milk. Babies need 75 -100 mcg daily. Some commercial brands of goat's milk formulas add extra folic acid. See your pediatrician for supplements or change of formula & evaluation of the bleeding.