Lab with loose stools

Question
I have an 8 yr old Choc. Lab who has had loose stools for the last 2 weeks. She is on thyroid meds for low thyroid. She has lost weight for the last 4 months starting at 84 lbs and now is at 77 lbs. She does not act as if she is in pain, she east normally and has a good appetite. (she will eat anything we give her) and her poop times of the day have not changed. The problem is when she poops its soft and almost looks like it is incased in a piece of skin. In the morning it is a large amount and in the evening its just a bit. Her vet has given her a pectin supplement to take for 4 days and it hasn't really helped. I am concern with the weight loss, she looks good! Her ribs aren't sticking out and her energy level is good esp. since she has been taking the thyroid. I am tired of the vet telling me its just her coming off her 6 wk penicillin regime for ecoli in the ballader she was fine until the regime ended. She has no temp and her blood and stool test were good
any suggestions?

Answer
You could try a bland diet for a week and see if it firms her up.  If it does, you could then slowly reintroduce her regular kibble.  

Bland recovery diet for dogs.

3 parts cooked rice, one part boiled hamburger or chicken, or cottage cheese. I think you can substitute boiled potatoes for the rice. Once in an emergency, we bought a plain baked potato from Wendy's.

This is meant for short time settling a dog's digestive tract. It is not the complete and balanced diet they need long term. I have seen it work.

The weight loss could be a good thing.  Your dog definitely should be narrower at the waist than the hips and chest. You should be able to easily feel the ribs, but not see them. Each dog is different. Standard recommendations are a good place to start, but each dog must have its food and exercise adjusted to its individual needs. Here is a link to a good illustrated guide, http://www.longliveyourdog.com/twoplus/RateYourDog.aspx