Switching from puppy food - upset tummy

[TheOriginalMrsMoss]

So puppy was on Skinners Field & Trial Puppy food from weaning and has done really well on it. We have mainly fed her on that plus added extras on top (diced apple, carrot, chicken, dried sprats, and some fancier kibble from Natures Menu). However, she's not that keen on the puppy kibble and the Natures Menu alone is too rich.

I tried her with some Hypoallergenic Duck & Rice Junior from Skinners mixed with her puppy kibble 25%/75% and she's gone from rarely an upset stomach (apart from eating the hose!) to bright yellow liquid! We've reverted back to puppy kibble and plain rice for now but she's not keen on it and picks out the rice.

I don't want to raw feed and I'm surprised that a hypoallergenic kibble in the same range could have such a different effect. Any ideas on what's likely causing the upset and any suggestions?

25%/75% is a very quick switch - it really needs to be done much slower than that. 10% new food at first, 90% old - it should take a good 2-3 weeks to switch them over completely to a new food.

It could also be that she's allergic to duck as a protein. Mine can't tolerate lamb based foods.