Highly recommend Joel Salatin's works - he has a really interesting perspective.

Here's a talk of his on Cows and Climate Change https://www.youtube.com/watch?v=4Z75A_JMBx4

From my recollected (watched that ~6 mo ago), the amount of land needed to grow food for his herd is less than the amount of land that would be needed to purchase it elsewhere, because the rotation of the animals keeps his fields fertilized and trimmed to the optimum length for fast growth. Plus, by rotating in chickens, he's double dipping a bit.

There are some people doing some interesting research into using herd animals to prep beds for annual vegetables: they let the animal graze as the seeds are starting to germinate, animals eat everything green. The germinating seeds are then able to fill the void left behind faster than anything else, because the farmer timed it properly.