I talked to the Cow/horse Vet about this after such NICE success with worming the cows using a pour-on wormer. They were almost instantly BETTER, with more glossy hair, filling out nicely.
She said that the pour-on is HARSH on horse skin, can actually burn it in some cases. She dealt with a horse wormed using the pour-on, who had lost the hair, was wearing an oozy spot along his spine. Horse was unusable for over 6 weeks with that sore needing to heal, then grow hair back in, before he could be ridden again.
So after hearing that story, I gave up on using pour-on wormer for the equines. Sure not worth burning them or scarring them when other wormers are easily available.
And one of our calves, with white over his back, did get sore after worming with the pour-on across the white area of skin. He was kind of a sensitive guy anyway, more touchy than other breeds we had. We then only put the pour-on wormer on his black haired spinal area, and just avoided the white backs on the other calves. The dun heifer never had any bad reaction, though she WAS really touchy about getting shots, even using TINY needles. She was "special" in a lot of ways.
Yeah I was thinking pour on was just too good to be true. Yes, and the chemicals in it. For cows it is a good thing, just not horses.
A friend in TX uses it on her horses every couple weeks. I would just freak if I caused skin issues on my horse. I had one chestnut arab gelding who got very reactive with the top spot, Freedom. Won't use it again on anybody. Now I have a black horse, and I would DIE if she got a white stripe down her back due to this stuff. She would look like a skunk! She is a fly sensitive horse, first one for me. She is already stamping at flies and it is only April. Gonna be a long buggy season for her. I am keeping up with my poop management. I do have a fly sheet, and fly mask, and will be keeping her legs sprayed. I also bought a riding fly mask. Both have ears.
For cows, yes, horses - probably not. THANKS ya'll!!!