rattler,
stay away from the generics they don't do that great of a job. You often get what you pay for. Cydectin, Eprinex, Dectomax and Ivomec are the leading pour-ons and seem to do great. I use Eprinex and find wonderful control. I also use fly tags, but usually don't put those in till a little later. A lot of time people will talk about rotating dewormers. If you rotate b/t the 4 previous mentioned you aren't doing any good. if you rotate you need to rotate b/t the Generic name (Ivermectin, Levamisol, Thiabendazole, Albendazole, Fenbendazole, etc...)
With that said there is no evidence of internal parasites developing resistance to cattle dewormers, so for internal there is no real reason to rotate.
Feed through wormers can be a problem. You need to make sure that each animal is actually injesting the amount of dewormer needed to be effective.
Failure of dewormer is usually a result of underdosing, using out-of-date product, or improperly stored dewormers.
Remember most of these have a min and max temp in which they can be stored.
