Originally Posted by KsKingBee
Since I have the ability to do fecals before and after worming perhaps I do not need to be worried about changing up the med I use? I would think that resistance build up would be more likely with underdosing.
Ummm, well, yes, maybe, not exactly....
Yes, you do have an advantage in doing your own fecals, and it is smart to tailor your worming to what you find. By the way, your home parasitology work is truly, truly impressive and amazing
Yes, you probably still need to be worried about changing up wormer class periodically.
Yes, resistance build up is more likely with underdosing.
But that's not the whole story.
Worming (or similarly, treating bacterial infections with antibiotics) resolves acute issues and restores animals to reasonable health. Few of us would choose to forego the life-saving benefits of either. But even with optimal dosing, sometimes a few, more resistant organisms may survive. They can then flourish and repopulate the host organism with a more-resistant form. As cycles repeat, more and more resistant organisms reproduce and higher doses of the medication are needed for control, until eventually attempts to control with that medication is futile. Under-dosing leaves even more resistant or partially-resistant organisms, and speeds the resistance.
By carefully checking fecals, you are minimizing the opportunity for resistance, but not eliminating it -- some undetected organisms may survive despite fecal exams. The resistant ones are the ones we are worried about here, because they can reproduce more of themselves relative to the numbers of susceptible (able to be killed with the medication) organisms.
When we change wormer class, we improve the odds of knocking out those organisms that may have survived the previous class, slowing the cycle of resistance by eliminating the bad guys via another weapon in the medication arsenal. This means using a medication which attacks the organism through a different biological route. That's why it's important to change "classes" of wormer periodically.
I love your vet she sounds awesome