Puppy getting diarrhea from new food

Hi, my 4.5 month old puppy currently eats purina puppy chow but my vet told me i should start to switch her over to a higher quality food. She recommended blue buffalo. I purchased BLUE™Life Protection Formula Small Breed Puppy Food. I got it 3 days ago. Ive been only making about 1/10 of her bowl the new food and 9/10 the puppy chow. But her stool is starting to become somewhat loose. Just had her out and it was straight diarrhea she then proceeded to wipe her butt on the ground afterwards. Should i be worried? Im hardly giving her any of the new stuff, could it cause that much of an affect?

She is a mini australian shepherd

Sounds very like something in the new food is not agreeing with her. Has the protein source changed (ie chicken to beef or lamb to chicken etc)?

Try to see what changes there are in the ingredients as it may well be that she is intolerant to something that has been added to her diet

Personally I'd revert to the original food only and see if she improves before assuming it's the new food. You could add a dollop of natural yoghurt to help settle her tum.
Has she been wormed?

There's a lawsuit ongoing in the US at the moment regarding Purina dog food. I haven't read it all as I don't feed that stuff but google Purina lawsuit and have a read.

Has her tummy calmed down? Trouble's advice about the yoghurt is great! That helped my Bella when she had an upset stomach.

Hello! I know it's been so long since this thread appeared, by the way how's your food? Hope she's okay now. What treatment you do for her?