> What do you think "trim" is here, and why do you think anyone would do it?

The animals are doing the trimming instead of the mowers. This isn't super complicated logistically; each takes tall grass and turns it into short grass. You can rent goats to clean up shit like poison ivy, even.

> How much do you think a hay field would grow in six weeks?

The one by my house grows maybe a foot in that time, which is why they rotate pastures. Even a handful of horses can keep an acre worth of pasture quite well cropped.