Depending on how your dog handles transitions, I usually change the kibble after every bag, which is about 1.5-2 months, and I have a couple of cases of different canned foods, and he gets a new protein source canned, which is about 6 days or so.
Glad my boy has a semi iron gut, I always switch foods cold turkey.
right now doing wellness core again! After this most likely champion. again! (I do buy differnt varieties)So I do switch as often as the bags are done! proabbly every two months maybe a little less depends! Oh and I change the wet food all the time. I buy differnt brands of good quality wet and just give the four dogs a quarter of a can in their evening meal!
There's no set rotation schedule, each dog is different and how often and quickly you rotate will depend on your dog.
When I fed kibble, two of my dogs could only tolerate one specific kibble each and of course they were on different brands of kibble. Because of that I could not rotate their kibble but I did rotate the canned food that they ate mixed with their kibble. I changed the cans every 3-6 days.
Now that I feed The Honest Kitchen and raw I rotate THK formulas every month and rotate between different raw, cooked and can food sources several times a week. They definitely get a lot more variety on their HK/raw diet.
If I fed kibble AND had a dog that was not as sensitive as mine then I'd probably rotate to a different brand and/or formula every bag.
I use to give both different kibbles and different canned meat for every meal. Also different protein sources each time. Guess I was lucky though - reading through the various threads its seems most dogs would tend to get an upset stomach from doing this.