Yes, the calf pooped yellow, as they normaly do, but in the morning it changed to brown-grey.
The problem is that I am only a trainee on this farm and farmers dont realy care what happend with it and this situation is not an alarm for them and i cannot understand this attitude.
I'd start by asking questions... you're a trainee, they're the owner, not your monkeys, not your circus. Some owners are incompetent, many are not and really do have reasons if you take the time to inquire politely.
For instance, is this one calf out of 3 on the farm, or one calf out of 3000? The latter situation isn't a cause for concern.
Be careful... if I had a clueless student with a bad attitude who wanted to grill me about my concern level for the random calf who died (of likely either pneumonia, diarrhea, or enterotoxemia - the reasons apparently healthy 10 day old calves die are not that complex)... that student likely wouldn't get the response they were hoping for. Be cautious how you've been perceived and how you present your questions.
Following that, realize you're asking for an answer that can't be given over the internet. There are so many variables raising calves, including management and feeding, that short of taking up several pages of posts asking and answering questions, there's no way to determine what killed this one calf. A necropsy would yield more information. You likely need a veterinarian to visit the place (this may already be happening at a management level)... but again, remember, not your circus. Do your job, look for additional ways to help out, be a good employee and *learn.*
