I have read that some dog's cannot handle going grain free. What does this mean?
Grain free foods are very rich and some dogs with more sensitive tummies have a hard time handling the richness of the foods, causing diarrhea and in some cases vomiting after eating. There are a lot of ways to reduce the chances of this happening, though, and you shouldn't let it scare you away from going grain free.
---Make the transition very slowly, mixing small amounts of the new food with the old over time.
---Remember to feed less of the richer foods. Overfeeding them will cause the diarrhea.
Also, am wondering about the whole rotation thing. I always thought I should keep them on one kind so it does not mess with their stomaches.
This is a common belief. It's not wrong necessarily, but it's also far from right. Variety is so important in ANY kind of deit, be it kibble, homecooked, raw, or any other way you could possibly feed a pet. (or human, for that matter) The more you rotate foods, the less likely it is for a dog to develop allergies, too.
Some dogs and cats transition easier than others and have tougher tummies. SOme dogs and cats have a hard time transitioning foods. This is where each dog is different comes into play. I always recommend transitioning as often as you feel your pet can handle it. For dogs who have a harder time, this might only be once or twice a year, and that's okay. You don't want to totally upset their systems. For other dogs, this might be every month. My cat, for example, never has any digestive upset. I can transition her in less than a week without any upset tummy or stool issues, so I change her food every bag. She can handle this.
Do I have to do the whole mixing foods for a week everytime I rotate
the simple answer is yes. There is no real rule on how long you should take to transition. I always just say as long as stools are solid during transition, you're on the right track. SOme dogs need to go slower, some can do it in a matter of four or five days. The only way to know is to start and watch stools and you'll know if you're moving too fast.