Yes, it is still advised to switch brands. I would not go longer than 3 months on one brand. Within a brand, all the different formulas usually use the same vitamin/ mineral premix, which means that they are all high in the same things and low in the same things and missing many of the same micronutrients. So switching to a different brand helps to even out those types of problems with kibble. And don’t forget that different nutrients support different probiotics and the more diverse the probiotic population is, the better the immune system is.
Switching after every bag is probably best.
