How would you say Boxer, the cart horse, fits into the climax in Animal Farm?

I think that Boxer fits into the climax in a couple of
ways.  The resolution offered is one where the pigs are able to consolidate all of their
control over the animals.  They have become "the new boss," without demonstrating any
real difference from the humans.  They wish to control everything, and this includes
history and memory.  They do not want any remnant of the past and this is why the pigs
have never retired any animal, though the promises about that they will.  In the final
analysis, the conclusion that shows that no animal can stand in the way of what the pigs
do or for what they wish.

Boxer fits into this condition in
a couple of ways.  The first is that he has outlived his usefulness as a worker, and
thus Napoleon sees it fit to send him to the Knacker's.  When Boxer's lung collapses,
his usefulness is over.  The pigs would not want to keep Boxer on the farm because he is
such a well respect figure amongst the other animals.  No animal could ever say anything
bad about Boxer and all came to admire his excellent work ethic.  Boxer not working is
more dangerous to the pigs' control more than anything else, as he could be seen as a
"cult figure" or one that would rival the pigs' desire for undivided attention.  In
this, Boxer becomes part of the pigs' desire to consolidate control when he is sent
away.  In wishing to severe all links to the past, the pigs end up sending Boxer, one of
the oldest animals on the farm, away so that he cannot be seen as anything but a figment
of the past that pigs like Squealer can rewrite to their own benefit.  In this, Boxer
becomes part of the novel's conclusion and its own thematic
development.