Everyone at our yard worms at different times with different wormers, some arent even wormed at all really (like once a year), we have never had any problems.
I do my own now, but before, when I was on a yard as I was responsible for tacking I bought the wormer in bulk and informed everyone when worming was due, worming was done on the same day and was always witnessed to save arguments. Incoming horses had to have a 5 day wormer.
As I'm the YO I do it myself after deciding with my vet which wormer to give. It cant be bought in bulk here and has to be bought from the chemists with a triplicate prescription and the medicine register noted.All medicines and treatments have to be registered and there are huge fines if youre caught with a register not up to date. M.
I do ours for the Yard but am an SQP so feel happy to do it.
I very strongly believe that all horses on the same yard should be done with the same drug at the same time.
I do it on my yard (where Im at livery)! Its a frigging nightmare, I only do it for the sake of the horses! It does work if you are willing to put the time in, are willing to sacrifice your wages temporarily & you dont mind being rude to liveries that wont pay!
At the beginning of each year the vet does the yard a worming programme, one of us (the liveries) then buys the years wormers in bulk (as we get a good discount that way), we all worm with the same thing on the same day. This has worked really well for us for the last three years, but we only have 15 horses.
All new horses to the yard are wormed and have to stay in for 24 hours before they are allowed to be turned out.