I've worked in chicken houses, dairies, and worked cattle, sheep, and horses where one had to deal with the poop day in and out. I've cleaned out chicken houses - 20-30 tons of chicken poop- with a scoop shovel. Ditto horse stalls, and we hauled cow manure out on a skid and slung it onto the pasture for fertilizer. I've appraised chicken houses, hen houses, turkey houses, and hog farrowing houses. I've never appraised a feedlot per se (just cattle auctions.) And we had a dog kennel and nothing gagged me worse than dog poop but dad built a huge kennel so that there was plenty of grass and dogs rarely had an odor related to their poop. But a couple of houses I've been in....they were almost too much. My assistant was also raised on a chicken farm and she agreed. A bad dog pooped house is worse than any chicken house.
OP's appraisal sounds like a C5 for sure, and maybe C6 if the structure has had the urine soak into the flooring, walls and baseboards, b/c typical buyers won't buy that, and will take into consideration the $$$$ required to strip it all out and try to start over.
Actually, I'm not bothered much by horse apples, but piles of doggie-doo, & especially cat mess?!... Gag a maggot! That is one of the hardest smells to get out of walls, upholstery, floors, baseboards.
Terrel, I'm a farm gal too, and the cows, sheep, chickens, and shoveling it all out then spreading it in the field with a manure spreader... well, that was just another day on the farm. I do think that we become used to some odors in our environment and tend to 'cancel them out' to a certain degree.
Did an appraisal on newer construction built on a former industrial-level dairy farm here where they packed in the animals like sardines so there had been mountains of manure. Anyhow, the odor was pretty oppressive in this new neighborhood, and I asked the guy, "Does the odor bother you?", and he responded: "WHAT ODOR!" OMG! Later, I saw they had installed pipes to burn off the methane, and this was near the (15) Xway, so many folks would take an alternative roads due to the concentrated acres and acres of odor. Out in the 'country' the cows were in the pasture, so a plotch over here and a splute over there didn't hit ya... except if they had pigs. 'Nuf said.