I don't think it is an odd statement. If you are feeding tubs or lick tanks, if you have wormed the cattle with a chemical wormer of any type, Ivomectin, safe guard, you name it, or if you have added any antibiotics to the feed say for pnuemonia or anything, it is gonna come out the other end of the cow. It then is not a "natural component" and the dung beetles and worms and others that break down the manure piles may not go to work on them or may not do it as quick as they would if the animals just ate grass and NOTHING else like nature intended in the grand scheme of things.
I am not saying that you should never do anything to or for the cattle. But it will change the composition of the manure and some of the organisms that do break down the piles may not work as well or as fast on them. I can't remember where I read a study on that. And I am not saying that it is the only reason for slow breakdown. But I do believe it can be a contributing factor.