Kenny,
I have never advocated using a pour-on dewormer for fly control... actually, I've railed against that practice here on these boards... it's misuse of the product that just speeds y'all faster down the road to selection of populations of nematode parasites resistant to that whole class of dewormers (macrocyclic lactones). Though I guess you could look at it as, "Well, we've already screwed the pooch on use of the MLs as an effective dewormer, might as well see how quickly we can select a population or hornflies that are resistant to them, too."
Pour-ons are the worst possible mode of administration... absorption is poor to begin with, and absorptive ability varies widely across breeds and individual animals. In a vast majority, they are not applied properly - how much ends up on the ground or on the sides of the chute?... and how many folks weigh their animals?... numerous trials have shown that even 'seasoned experts' are notoriously poor in judging actual weights of animals... too much underdosing going on.
Now, as to that cow... there might be Jersey in the woodpile, but she is NOT pure Jersey... no dished face or bug eyes... not much of an udder, either. That 'wild color' pattern can come from a whole lot of places... Red Angus, Tarentaise, Corriente, etc. She might make some milk, but I'm not betting on more than enough to raise her own calf.
