Production RIRs aren't stocky, but much more like Leghorns in body type. Racy. By the time you actually see intestinal parasites in the poo, there's a lot of them! You can have fecals checked at your veterinarians to know what's going on. Some flocks will have lots of intestinal parasite issues, and some nearly never. It depends on what's present at your place. Mary
The truth of this is why there is a complete divide in management. Some use medicated starter then de-worm every year. Others like myself don't do either. Each climate, soil and parasite density is different. Stationary pens used for years will get "poultry sick" soil too. Meaning you'd want to use medicated starter and de-worm flock every year.
I'm in the frozen north and only use a stationary pen in winter. Knock on wood- with use of pot ash in dust bath areas I may never need to treat the birds.