@Riger I don't think Mammoths here necessarily HAD to eat a lot to sustain themselves, at least not till they already grew huge. It's probably just a strategy that worked out for them: they eat lots, grow big and can afford to give no shit about anything else as they just endlessly migrate and eat everything on their way. that's a loop of cause and effect as long as there are always huge mammoths to protect smaller ones that's just growing up.
so I suspect by domesticating it and regulating it's diet it will simply become more like elephant.
Agriculture was first developed around the Gobekli Tepe and Catalhoyuk areas 11,000 years ago, not 6000. And beer and wine was brewed from wild grains and fruit long before that.