My situation started last April. My 8 yr old mare was rubbing her tail & butt area raw. Because she has been wormed on a regular schedule and I do rotate the wormers, (I should also mention that I have 3 other horses without this problem) the local vet decided to put her on steroids. So I did, and the rubbing continued. (In the mean time, I moved her up to a pasture in N. Minnesota) Then I found a fresh pile of her manuer loaded with live wormes. They looked like white spagetti with pointed ends. Than another vet (up in MN) had me repeate a dose of Zimectrin Gold once a week for 3 weeks, which I did. The itching & rubbing stopped. I repeated the dose approx. 1 month later to get her on schedule with my other 3 horses. Now 2 weeks later, and back in TX, she made another pile and it was full of a bunch of dead white wormes. But now it has been 1-2 weeks and she is rubbing her butt again!! It has only been 1 month since her last dose and I do believe that I am even over-dosing her. She weights approx. 1350 lbs. and I'm giving her enough for 1500 lbs. What does one do to get control of such a chronic condition? I plan to give her another does of Zimectrin Gold today, but when is it considered to much wormer?
p.s. She rubs so much that she is tearing down the hay feeder, salt block holder and even pushes out some of the fencing in her stall. I've had to lock her out and leave her out in the pasture to rub on the mesquite trees. I've had horses for 20 yrs. and have never encountered this before. HELP!!