with the pour-on invomectin there is a significant advancement in the area of parasite resistance. To many people have routinely used ivomec as their only wormer choice and they routinely apply it on a scheduled basis.
I with the same adivce from the two vets I deal with and a separate vet who is a personal friend ( no longer practices he went back in the Army), we worm only when there is evidence of a worm problem, ie physical symptoms backed with fecal analysis.
Then when needed we try to change on some kind of irregular rotation the actual dewormer medicine we use. ie no simply ivo-mec followed by off brand ivermectin but a totally different drug to avoid the potential for parasite resistance to specific medicines.
We rotate too. This year I will use Dectomax in the spring, and a different one in the fall. The Dectomax works well here in the spring. We don't have the resisitant internal parasites here yet. The resistant ones seem to be more in the southern states.
True the resitant strains are more prevalent in the south. I'm curious if that might have a correlation to our longer warmer seasons providing a longer cycle of parasites????
We did use pour-ons for a long time, but lately I'm favoring injectables, as with a good working pen lay-out injections are almost as fast as the pour on if there are any other tasks to be completed at the same time, such as ear-tagging or dehorning.
Might be his1911.
We rotate our pour on's. We do them at branding and again at weaning roughly 6 months apart.
Talked to our vet about injectables, but he said for up here in Montana there is not a huge need for it. We have more external instead of internal parasites.
Since I try to AI my entire herd each year, I prefer to be as gentle as possible on my cows. The less I stick them with needles the better. That's one reason I prefer the pour ons. Seems like every time we run them through the chute, we cause them pain. No wonder they balk at going in.