In cattle at least, they spend much of their life grazing before going to feedlots.
https://www.sciencedirect.com/science/article/abs/pii/S22119...
However, we shouldn't assume health and diet are simply a matter of calories as input. Even conceding that beef isn't a particularly good choice for human health given it's saturated fat content, I don't know that replacing beef in the diet with corn would necessarily result in better health outcomes.
Options range from other crops, parks, leaving it fallow, solar, growing bio fuels, etc.
Realistically we aren't going to replace beef any time soon, but who knows what happens in the future.
https://ourworldindata.org/meat-production#efficiency-of-mea...
The underlying numbers seem reasonable with US airlines use ~10 billion gallons of fuel per year while the US produces ~15 billion gallons of ethanol being freed up by the rise in EV's.
Globally things aren't as rosy, but freeing even 1/5 of the land devoted to grazing, alfalfa, and feed corn would go a long way. Reducing US beef consumption would have positive health impacts. So from a policy standpoint shifting the specific subsides seems like a good idea.
Even if we can't get net zero the more we can cut quickly the longer we have to finish the job.
We care quite a lot about the form energy takes not just absolute quantities. $4 gets you ~200/kWh from solar enough to drive ~800 miles, or enough premium gas that to send an equivalent car less than 1/10th as far. Similarly, people happily pay 30c/kWh for 300kW fast charging because waiting around is it's own cost.
In comparison with bio fuels, green hydrogen is wildly energy negative wasting ~80% of input energy and you need to completely redesign all passenger aircraft.
Yes, I've already mentioned this:
>However, we shouldn't assume health and diet are simply a matter of calories as input.
In the context of the discussion, it's an error IMO to compare energy as if they are interchangable. People aren't just consuming beef just for it's caloric value. The "form" of energy (protein & fat) is an important consideration too.
>In comparison with bio fuels, green hydrogen
The constant digression of a topic focused on nutrition into one merely about energy makes for a tiresome conversation and largely misses the point. Just because you can make a loose connection with the topic at hand doesn't mean that discussion is relevant.
US produces about 27 billion pounds of beef, roughly half of that weight comes from feedlots where they eat ~80% of feedlot calories comes from grains.
There's a bunch of numbers tossed around but it's something like 60-70 billion pounds of grain to get those 27 billion pounds of beef.
Grain crops store really well on their own, as in decades, cows on the other hand need to eat constantly.
What they are good for is eating indigestible cellulose like corn stalks, but modern farming is largely feeding them grains specifically cultivated to feed them.