Stepping back, it should be obvious that carnivores such as felines and canines provide an important source of data relevant to this question. Carnivores have colons, and they are not normally in ketosis unless food is scarce. Either their colons don't need butyrate, or they are getting sufficient butyrate from some other source. As it happens, there are microbes that ferment amino acids in to short chain fatty acids (SCFAs), including butyrate. Carnivores are known to get "animal fibre" from their prey. That is, amino acids from incompletely digested animal parts reach their colons and are fermented. In particular, in cheetahs, casein, collagen, and glucosamine have been shown to result in butyrate production comparable to fructo-oligosaccharides [Dep2012] .