Mike CHS
Herd Master
One thing comes to mind....do you give enough, when you worm? My vet always said, kill them, don't stun them!! With the safety margin of overdose with MOST products, it's something to consider. Do not under dose. Also, the condition of pastures, rotation options for you and your area weather, other animals there, all play into the life of worm viability and reinfection.
It's a crap shoot.....we know that certain herbals and forage help keep numbers down, so using that with everything else helps. I never kill the "weeds" in my fields! Well, except nightshade, if I see any.
Many farms estimate weight and in some cases they are pretty accurate and in as many cases they are way off. We worm after running them over the scale so it may be a factor. I'm usually pretty good at estimating weight but I have had many times that I was way off.