A sentence from Animal Farm...
the bits, the nose-rings, the dog-chains, the cruel knives with which Mr. Jones (had been used) to castrate the pigs and lambs, were all flung down the well.
Why use passive voice here? Isn't "Mr. Jones use...."?

Question

A sentence from Animal Farm...
the bits, the nose-rings, the dog-chains, the cruel knives with which Mr. Jones (had been used) to castrate the pigs and lambs, were all flung down the well. 
     Why use passive voice here? Isn't "Mr. Jones use...."?

Answer

I searched and found your original text, which is ungrammatical.  So your question was a good one.  However, another source showed a different variation - "had used" (active tense).  This is correct.  See: https://books.google.co.uk/books?id=vMirZ_8_encC&pg=PA153&lpg=PA153&dq=the+bits,+the+nose-rings,+the+dog-chains,+the+cruel+knives+with+which+Mr.+Jones&source=bl&ots=etw6W52b9I&sig=D-VKdwqoVyNV7tvmaOdPGiPuFec&hl=en&sa=X&ved=0ahUKEwjcipDbsaLNAhXJCMAKHe2zDn0Q6AEIKjAC#v=onepage&q=the%20bits%2C%20the%20nose-rings%2C%20the%20dog-chains%2C%20the%20cruel%20knives%20with%20which%20Mr.%20Jones&f=false

Answer

Thank you!!

Answer

Are you sure your quote is accurate? 
This is a literary work and the author may have chosen the passive to vary the style or pace of the narrative. This is perfectly acceptable.