No no no no no!!! DEFINITELY not in the straight form, as she will easily get toxicity from it!! You're better off giving it to her in a loose-mineral form with other minerals like iron, cobalt, salt, copper, manganese, etc. Cattle only need like 0.5 mg of Selenium per day, and only if you are in an area that is Selenium deficient. If you are NOT in an area that is NOT Se deficient, then you can completely forget about feeding a dairy cow selenium!
A cow. Or, if you want to go into specifics, a dairy cow.
It gives more milk than what it would normally produce for its calf. That's what constitutes a cow for being a dairy cow.
The dairy cow.
Dairy
That all depends on the breed. Are you asking about a dairy cow or a beef cow, and what breed of dairy or beef cow?
Yes, when they are to old to breed and the milk production drops off they are eaten. Smaller (family) dairies usually care more about their cows and will sometimes give a cow a year off if she is normally a good milker, but eventually she will have to be replaced by a younger cow. On occasion a favored cow may be turned out to field and retained as a farm pet or mascot. That is if it is a small grass based dairy and not a confinement dairy operation.
Dairy cattle like Holsteins, Brown Swiss and Jerseys.
A dairy cow would die a matter of a few weeks before she even gets to the point where she is deemed "feral." I would see a beef cow becoming feral, yes, but not a dairy cow.
A farm
There's not really an answer... You just call it a cow...
cow
Not at all. Grass is eaten by a cow, not produced by a cow.