Changing dog food can cause an upset stomach in your Golden Retriever, and this can lead to diarrhea.
This applies to a new puppy that may have been raised on a different brand than the brand you plan to use, or to an older dog that you have decided to switch from what you have been feeding her to something different.
If for any reason you do need to switch to a different type or brand of dog food, make the change over to the new brand slowly.
Add a little bit of the new brand to the old brand gradually.
On the first day of switching dog food brands, make the mix about 1/4 of the new brand, and 3/4 of the old food.
Every day add a bit more of the new brand, while lessening the old brand. You should be able to switch completely over in about a week, and your Golden will not have an upset stomach by doing it this way.
If you bought a new puppy, you should have been given some of the puppy food that she has been eating. This should be enough to use while you combine it with the new brand you will be switching to.
If there is a medical reason or any other valid reason in which you need to make a quicker switch over (such as a momma giving birth to puppies and needing to go on puppy food), then do a 50/50 mix for 2 or 3 days to help lessen any side effects.