Hill's Science Plan Adult 1-5 Large with Chicken - dog dry food

We have a Scottish Collie and we always used to buy the small-sized kibble, but now we've bought the bigger kibble and she won't eat them anymore. I think she finds them too big. If I break the kibble up, she will eat them.

I don't know if it's the kibble, but my pet doesn't go to the toilet like before and is having trouble doing its business.