Replacing zinc oxide (ZnO) in diets is even more difficult than replacing antibiotics. Not only the exact mode of action of ZnO remains elusive, but this additive appears to work on top of everything else -- including most antibiotics -- that has a controlling effect on gut microflora. And not only that, but it also works equally well in piglets with digestive disorders (stopping diarrheas) and healthy piglets (improving growth performance).
To replace ZnO, a complete reformulation of the basal diet is required to achieve two goals:
- Remove or reduce ingredients and nutrients that promote proliferation of harmful gut bacteria. For example, avoiding ingredients rich in iron and reducing dietary protein specifications both help in depriving E.coli from much needed nutrients for growth.
- Use ingredients and additives that promote and sustain a healthy gut microflora. In the absence of antibiotics, ingredients that promote a healthy microflora include those with a high concentration in functional fibers, whereas additives such as copper sulfate will control to some extent pathogenic bacteria.
In the end, ZnO-free diets are not impossible, but they cannot be achieved without restructuring a diet that has been designed to rely on ZnO -- more or less the same story as with antibiotics.