If you mean "mixed flock" as in chicks, pullets, layers and roosters - yes! Just provide oyster shell free choice for your girls
Be watching bird that produced this feces closely. I doubt it is a diet issue cause the strange appearance of the feces. I can make out uric acid as the truely white part. The off-white stuff appears to be feed that is going through with little processing beyond trituration (grinding by gizzard action). Typically the bulk of the feces will take on a browner look which is not evident in image. Secondly, the feces has a lot of fluid in it indicating bird not scavenging water from digesta. That could be because diet is exceptionally hydrated at time of intake like you can see when bird consumes a lot of fruit, or gut is not functioning properly and bird is facing risk of dehydration if not able to drink enough. When my birds eating enough fruit to cause runny feces, the pigments from fruit often pass through enough to color feces.
