How is boxer betrayed by the pigs in the book Animal farm?

Boxer fell and was injured badly. Squealer said he was arranging to take Boxer to Willingdon Hospital but when the van came, it read "Alfred Simmonds, Horse Slaughter and Glue Boiler, Willingdon. Dealer in hides and bone-metal. Kennals supplied". The pigs were taking Boxer to the knackers to be killed.