Some of the most famous standardbred poultry breeders of all time ended the hatching season by turning the breeders out on range with nothing else but oats to eat. This brought them back into condition to compete at fall shows. Winning poultry shows was how these people made their living. People like Halbachs, Miller, Kriner, Stauffer, Davidson, on and on. All the legends.
The commercial poultry industry uses straight oats as feed for laying chickens and turkeys to "soft molt" them when they are recycled. This is the feed used to hold them in good condition as a little bit of weight and all the fat is taken off them before bringing them back up to weight and into production. Oats is all they eat for two or three weeks.
The oldtimers I knew thought of oats as the nearest to perfect feed that any single grain could be.
When I raised Runner ducks oats were at least half of their diet after the breeding season and for the growing birds. In the winter the diet was 1/3 oats.
Chickens, horses, cattle, sheep and hogs- all were brought back to condition and out of poor digestive health but practicing the old husbandry technique of "get them on oats and pasture."