I look for calves that are depressed. As KLo said, head down, ears drooping, glassy eyes, heavy breathing, rough haircoat, calves that separate themselves or are slow to come to the bunk. These are calves to pull and check temps and probably treat. As the old saying goes "pull 'em deep", better to pull more than necessary than not enough of them.

You will have to stay out of sight, or stand very still for a very long time in order to get a real view of the cattle. Cattle that are sick will not show you symptoms as a natural defense mechanism - they won't show weakness to potential predators. If calves are showing symptoms when you just walk into the pen, they are really sick.

Stools can tell you a lot, but I also think a lot of folks overreact to them. On new cattle coming in, they will naturally be loose because of the stress of shipping, erratic intakes, and adapting to new feed ingredients they aren't used to. Looseness doesn't bother me, but watery does. Cocci is a major stressor that will often lead to respiratory disease. I will always start cattle on an ionophore in order to get ahead of cocci, and also use Amprolium at feedyards that have a history of chronic cocci.

Once cattle are up on feed these are the clues I look for in stools: On a typical feedlot ration, I expect the manure consistency to be somewhere between pudding and gravy. Grain in the manure tells you the rate of passage is too fast - cattle are rushing to eat because you are behind on feed deliveries or there is a lack of bunk space. Manure should be feed colored, gray color in the manure indicates acidosis. If you take a manure sample and wash it through a mesh strainer and there is slime left in the strainer, that means they are sloughing off tissue from their intestines and have or had severe acidosis. Manure that can stack like cow pies indicates cattle that aren't eating enough and/or are sorting the roughage to eat and are probably sick.