> Sometimes you'll be doing consecutive months of 13hrs/day labour, sometimes you'll have 75% of the day free, every day, for a few weeks.

That depends greatly on the farm in question. I grew up on a dairy farm, and there was no such thing as a break from work unless we hired someone to take care of the cows for us. They are fairly constant in the amount of work you have to put in (I imagine other livestock are similar but that's outside my experience).