Switching food

It really depends on the sensitivity of the dog in question & how similar the formulas are within the same brand. Many brands have very similar formulas with just a change in the base protein (they will often advertise that they are created for 'rotational feeding') As long as the dog doesn't have any particular sensitivities to different proteins, and/or physical digestive issues that cause problems with variety, then I'd generally say that the more you switch up foods (both protein and brand) the easier the transition will be going forward.

One thing to keep in mind is this - most brands use a 'premix' of added vitamins/nutrients which is used throughout their brand, regardless of formula or primary protein. Rotating within a single brand doesn't protect your dog from deficiencies caused by limits in that particular premix. Best case scenario is to rotate both protein AND brands, so you're getting a (potentially) better coverage of all micro-nutrients included in the kibble, which will differ - often greatly - between brands.

We do the same as LeoRose for our boys, but we know they're both quite tolerant of diet variation. With Sam, my first dog, I started this kind of organically - I'm on the anxious side, so I'd do 10-14 day switches. Then as I saw him managing that with absolutely no problem I relaxed and started doing closer to a 7 day switch, then closer to a 4-5 day switch, then a 4 meal switch (so closer to two days). Each time he showed no difficulty switching. Now we just cold turkey start in on a new bag when we're done with the old one. He might get a single mixed meal, but that's only because there's not enough left of the old food for a full serving.

So if you aren't sure how your pup handles food transitions, it might be worth it to start with a slow transition the first couple times (a week is probably fine, two was definitely excessive on my part, haha), then if that goes smoothly you can gradually cut down the transition period to figure out how long of one - if any - your pup typically needs. I confess with Frodo we did more of a "try it and see what happens" approach with switching cold turkey and it worked out fine, but that is running the risk of digestive upset, including the dreaded "rocket butt".

I think a lot more dogs do fine with switching foods than we realize, just because so many dogs do eat the same formula their entire lives, but the consequences when a dog can't handle the transition sure can, uh, leave an impression (and burn a few nose hairs)! So I get why people don't push it.

I like to vary brands and formulas partially because I feel like it gives me more flexibility - because I have a catalogue of brands and formulas that 'work' for my dog, I don't have to worry as much about the store being out of stock, recipe changes, recalls (I still have to worry if my dog is eating a contaminated batch, of course, but I'm not scrambling to find a replacement), or even something being discontinued. I also believe that it's more enriching for my dogs to have variety in their diets, although I acknowledge it isn't necessary and I'm anthropomorphizing a bit.

In general, so long as a food has passed all the necessary testing to confirm that it's complete and balanced, I don't believe that rotating gives any particular benefit in terms of nutrition. However, when questions arise like the DCM scare and the question of whether legume-heavy diets cause problems, I do feel more secure knowing that my dogs are eating a range of diets - some grain inclusive, some not, some heavy in legumes, some not - so if there's a cumulative issue with a certain ingredient being fed over a long period they're a little more protected.

For the record, I personally believe the DCM thing has been blown significantly out of proportion and the actual risk - if there is one at all - is miniscule, although I absolutely support continuing research so we can get definitive answers. But when it first came out, knowing my dogs were on a rotation diet was reassuring.

However, being able to rotate is absolutely a privilege, both because I have dogs who tolerate it well and because I have the budget and access to quality brands to make it feasible. I'll never say it's necessary to have a healthy or happy dog, and in some cases with sensitive dogs or dogs with special dietary needs, it can definitely do harm.