A feedlot induction drench for internal parasite control is advised for cattle under 2 years old and if droughted, weak stock. Treatment for fluke is also recommended if animals have come from fluke areas.
Worming of pastured cattle at the time they enter the feedlot is cost-effective only if the load of parasites they are carrying is great enough to reduce the rate of gain. The decision to worm young cattle can be based on abattoir feedback or testing. Drenching incoming cattle originating from regions with heavier worm loads makes economic sense.
Once cattle have entered the feedlot the chances of re-infection are low. There is no transmission as roundworm eggs and larvae do not survive in feedlot conditions. However, the parasites inside untreated wormy cattle will continue to thrive unchecked, causing diminished performance and reductions in health throughout the feeding period.
Internal parasites have the greatest impact on rate of gain when cattle are on low energy levels which are typical of receiving or backgrounding rations. Therefore, worming feedlot cattle when they are processed into the feedlot will give the best returns.