injectable dewormers

[DallyCash]

Looking at using an injectable dewormer this spring on our cows (regularly dewormed 2x/year) and my father in laws cattle (maybe hit with a pour on as they fly off the trailer into the pasture). I would like to use the same brand for both as we need just under 500cc. the brands I'm looking at are:
Cydectin $141.49
Ivomec $142.99
Ivomec Plus $187.95
Dectomax $150 (on sale)

I'm leaning more towards the dectomax, just because it seems to be the better bang for the buck. my worry is that if the FIL's is over loaded with parasites, could this cause them trouble? also, if his are bred (would only be about 10 of 30) they would be due April 18th. Again, if they are over loaded with worms and that heavy bred, would that cause them issues? These cattle do not have the best nutrition, and are quite thin. body scores of 2-4.

Any suggestions?

 

[Lucky_P]

Unless you're in an area where liver flukes are present, you don't need the Ivomec Plus.

It's a flip of the coin - all three are members of the same class of anthelminthics (kind of like choosing between a GMC and a Chevy pickup), and differ primarily with respect to comparative potencies. (Cydectin is kind of like the 'last-ditch' weapon when you've selected for populations of parasites with resistance to the macrocyclic lactone (avermectins) group of dewormers)
Just be sure you're using 'name-brand'... studies have shown that while the generics may 'satisfy' requirements that they contain the exact same % of active ingredient as the original... efficacies for some generics have been pretty poor.

No issues with this class of dewormers - all have a wide margin of safety. Removing the worms is a good thing.