I do leave a tennis ball size amount over the big holes to give them a bit of protection. If I see the big ones then i'll pick them out of the barrow - they do a lovely job of aerating the soil and fertilising.
I also keep horses in after worming as wormers in poo can kill them sadly.
We seem to have 2 types small ones - woodlouse sized and some massive (see pic of hole below) they are bright iridescent blue underneath
Unless your land is over grazed poo-picking does more harm than good, as it removes the nitrogen which should be going back into the soil, as well as disturbing the minibeasts/local fauna.
I find my fields are grazed very unevenly if I don't do any collection while they are in there. I spread my muck heap on the fields spring and autumn to put goodness back in and then rest for 4-5 months.
My husband does query the point of hours digging poo out to then pay someone to spread it back over again - but I think it suits my land.
Mine was a livery yard so on 8 acres we have 11 tiny fields and no practical way of removing all the fencing so they rotate often.