Domestication can change diet in mammals

One of the central arguments for releasing breeding-back results in the former range of their wild type is that they very likely fulfill the same or a very similar ecologic niche, as domestication is thought to affect mainly the morphology and behaviour of the animals but not the internal physiology. A study published this year identified a number of genes in domestic dogs that likely were changed due to domestication of the wolf, including genes that play a key role in starch and fat digestion, suggesting that dogs adapted to a more starch-rich diet relative to wolves: 

The domestication of dogs was an important episode in the development of human civilization. The precise timing and location of this event is debated and little is known about the genetic changes that accompanied the transformation of ancient wolves into domestic dogs. Here we conduct whole-genome resequencing of dogs and wolves to identify 3.8 million genetic variants used to identify 36 genomic regions that probably represent targets for selection during dog domestication. Nineteen of these regions contain genes important in brain function, eight of which belong to nervous system development pathways and potentially underlie behavioural changes central to dog domestication. Ten genes with key roles in starch digestion and fat metabolism also show signals of selection. We identify candidate mutations in key genes and provide functional support for an increased starch digestion in dogs relative to wolves. Our results indicate that novel adaptations allowing the early ancestors of modern dogs to thrive on a diet rich in starch, relative to the carnivorous diet of wolves, constituted a crucial step in the early domestication of dogs.

Paper on nature 

The case of megaherbivores is surely different from the domestication of the wolf, but it is interesting to see that diet can change due to husbandry by man.