The most important ones are ostertagia, cooperia and T axei. The problem with these worms is that they are not all killed by one drench family therefore using single active drenches (e.g. abamectin) is not appropriate in cattle less than a year old. Ostertagia is easily killed by MLs (the mectin family), but are very resistant to levamisole (clear drench). The exact opposite is true for cooperia—it is very easily killed by levamisole but resistant to MLs. The BZ family is average at best at killing them. There is NZ data available that shows that cooperia is a growth limiting parasite. If your cattle have a cooperia burden they will have poorer growth rates. Once cattle are over 15 months they build an immune response to cooperia and it is no longer an issue therefore single actives can be used in older cattle.
For these reasons it is very important to make sure that when you are drenching your weaner cattle (up to 1 year old) you use at least a double combination drench (or a triple). Single actives will not do the job. Options of drenches that we stock are:
Orals: Scanda®, Corporal®, Converge®, Oxfen C Plus®, Arrest® C, or Matrix® C (triple)
Pour on: Boss®, Eclipse®