That's interesting. .. I've never heard anyone claim them to work just purchasing one. At any rate, for me to order them for my corrals, would be $52 initially, then if I bought them again each month is $29. That's way more than I can afford for fly control. :/
I don't think I stated anywhere that either would be difficult. Fly predators are expensive... I certainly can't afford them.
As for the availability of AI services... well that certainly depends on where you live. The closest AI service to me is over 4 hours away. If she gets say a dexter, then...
Or where I live for grazing cattle it's 35 acres per head, lol.
As for the original question, I would go with approx 750 sq. feet at a minimum per cow. More space if you have it... cows need to walk to keep those hooves trimmed back. Also to take into consideration would be low/high spots and...