A. I would check the bag and make sure the food hasn't spoiled. It's strange all four dogs suddenly decided they don't like it. It shouldn't appear moldy or have any different smells. I would be tempted to take the whole bag back to the store (if they allow you to) and exchange or return it.
There will be differences bag to bag, even with the same brands as each batch may vary some.
You can always switch to another brand
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