GMO intestinal commensals

Big organisms are full of microbes. Mostly they reside in the gut. There is increasing awareness that these things influence metabolisms. Animal operations crudely try to improve weight gain of their animals by killing off their intestinal microbiota with antibiotics, and so presumably decreasing competition.

I propose as a first step towards domesticating the interstinal jungle, that well established commensal organisms be bioengineered to express the enzyme needed to break down keratin. Keratin is pure protein but is only digestible by certain organisms. If effective, domestic animals should derive nutritional benefit from waste wool, hair, feathers and the like. Cellulose can be next on the list. It may be that the engineered organisms are outcompeted by the wild types - probably one would need to reintroduce new ones periodically in the feed.

After proven effective and beneficial one could introduce these same commensals into humans, enabling nutritional benefit from items previously not on the list of "food".

If for nothing else this would be a fun throwaway aspect of a scifi set in a Mars colony, where the colonists have shaggy cows and a diet of milk and hair balls.