Maybe presenting the facts in a different light or getting another person to confirm the outcome of this problem might help to convince the manager.
For example, another assistant manager or someone who has this manager's ear could say some of the same things. This has a way of working. OR going to the owner, as a last resort.
Presenting in a different light could be another way. By this i mean, "Did you know..."
1. when a cow sucks off another cow, that calf will wean lighter making less money
2. the calf will find supplement elsewhere depleting another calf....and so on
3. a cow who supplements her calf and a cow or two will lose body condition and will be a poor breed back. Now if you have bulls in all year, this would not be noticed. But if you have a tight breeding schedule, it will stand out like a sore thumb.
4. a late cow will bring a lighter weight calf.
You will need facts to back this up so you are going to have to keep some records. Then when the manager chats about how poor this or that calf was at market, or if passing if the two of you are chatting about the herd, and the manager remarks at...that calf being a poor doer, you can then bring up some reasons why.
It is going to take some thinking out side the box on this one. Some managers are closed on ideas from some people, but not others. Some managers and people like to come to some realizations on their own and no amount of brow beating is going to change their minds. For people like this, they need to see the facts on paper of a particular instance...maybe several times.
Andt then there is the type that just feel they know best and to heck with anyone else...those are buttheads. Or they just do not care. So many animals that a live calf is better than a dead one no matter the cost.
Try it from a different approach in time. Start by keeping records and maybe documenting everything you see with this calf. In the end, hard to dispute why this calf is pottied or a dink.
Best of luck
