To make the subject somewhat clearer, let's review the facts. Animals that graze forage will likely ingest parasite larvae most of the grazing season. As animals age, they develop some immunity to these parasites. Deworming calves at weaning is nearly always cost-effective, whether they are moved to another pasture or placed in a dry lot. Nearly all parasite transmission occurs on pasture.
Transmission is unlikely at extreme temperatures.
While developing a parasite-free animal would seem to be the ideal goal, it is nearly impossible and probably not desirable. First, the cost of deworming would exceed the gain and secondly if the parasite free animal were exposed to parasites, the disease would be extremely severe due to the lack of built up immunity. There are numerous, cost-effective programs for parasite control and you should formulate a plan with your herd health veterinarian. Here are a couple examples for spring calving cow herds. The young cows are more likely to be harboring parasites due to a lack of immunity.