You're just looking for an idea of how many chickens to effectively break up the cow poo and eat the parasite larvae, if I'm reading your post correctly.
Not sure that there's a definite number as it probably depends on how big each daily paddock is, how resistant your cows are to parasites, general parasite load for your
land, quality of the forage for the chickens, types of chickens, and so on.
That said, I'd probably just take however many chickens you have (assuming we're talking 10's not 100's or 1000's) and start by running them all 3 days behind your cows. If that's obviously too many, cut it down by half. If it's obviously not
enough, start working on buying/breeding more chickens. Over the space of several months to a year you'll dial in the number for your situation.
It's been a while since I've seen any Salatin videos, but I want to say he had around 20 cows he was rotating around. And it seemed like he had around 100 egg layers cleaning the pastures behind them. So, if my memory is correct that would imply 5:1. But I could be WAY off.