Yeah, this is a complicated and scary issue. I fed Winston grain-free food the last seven years of his life, mostly because he had weight issues and the grain-free food helped keep him slim. As far as I know, he had no issues. Not sure if his final labs contained a taurine test. If they did I'd be interested in the data point. I've been paying attention to this issue, as Walter has a slight heart murmur, even though Shih tzus are not one of the breeds thought to be predisposed to dietary DCM. What I'm curious about is:
1. There is concern that grain-free diets are leading to the low levels of taurine, which in turn causes the DCM. What isn't clear is whether there simply isn't enough meat protein (vs. plant protein), or whether the peas, lentils, legume seeds, or potatoes are inhibiting proper absorption of taurine. Depending on the answer, the dog food one chooses might be different. If it's the former, grain-free manufacturers may just supplement taurine to ensure the nutritional need is met (indeed, many have already gone down this path). However, if the peas, lentils, legume seeds are blocking absorption, a lot of companies will have to reformulate their food.
2. I've been feeding grain-free Kirkland Domain for 2-3 years, as it's hard to beat Costco in terms of quality dog food at low prices. My dogs have always done well on it. But it's got sweet potatoes (2nd ingredient), peas (3rd ingredient), potatoes (4th ingredient), and potato fiber (5th ingredient). That's a bit scary, even if the science is still out.
3. My vet is still skeptical about the linkage at this point in time. Without more conclusive research, it's hard to know exactly what mechanism is driving the increase in DCM diagnoses, and how prevalent it might be.
4. My cynical side keeps coming back to the fact that all of this is rather convenient for Purina and the other mainstream/traditional dog food manufacturers. According to this article, grain-free pet food had sales of $3.4 billion in 2017 and now comprises 43 percent of market share. So they can most certainly take advantage of a panic, and take back some of that market share.
5. This is not to impugn the work of veterinary cardiologists working on this issue, as it is most certainly a serious problem. But unfortunately they're probably still a few years from sorting this out.
6. My plan as of now is to switch Walter to Kirkland Signature, which is a chicken and rice formula. It does contain potatoes and peas, but they're pretty far down the list of ingredients. Unfortunately, Costco stopped carrying it at our local warehouse in favor of the grain-free line. I contacted them about stocking it, but was just told to leave a comment card next time I shop at the local warehouse. You can order it online, but doing so jacks up the price.