How does Shylock use animal imagery to establish his obsession with Antonio's pound of flesh in The Merchant of Venice?

Shylock is discriminated against early in the play and treated badly. Not only Antonio but his annoying friends, Salerio and Solanio, use language toward Shylock that seeks to dehumanize him and to demote all Jews to a status not much higher than animals. Their moral blindness seems to prompt Shylock to take revenge on the same terms.
When agreeing to the loan, despite the Christian's persistent insults even while asking for a loan, Shylock seems to playfully throw in the bizarre terms of the contract: Antonio's forfeiture would earn Shylock a pound of flesh.

A pound of man's flesh taken from a manIs not so estimable, profitable neither,As flesh of muttons, beefs, or goats.

This seems like a jest, for in a world where money is a primary value, the idea of taking human flesh makes no sense. Antonio is happy to agree. Whether Shylock seeks to trap Antonio here is debatable. No one has reason to expect that all of Antonio's ventures would miscarry, so Shylock may in fact be offering this condition to show his "friendship," as he claims. Losing Jessica to elopement with a Christian seems to be an inflection point in the play for Shylock.
In the trial scene, then, he delivers his chilling speech that turns the tables and dehumanizes Antonio:

You'll ask me, why I rather choose to haveA weight of carrion flesh than to receiveThree thousand ducats: I'll not answer that:But, say, it is my humour: is it answer'd?What if my house be troubled with a ratAnd I be pleased to give ten thousand ducatsTo have it baned? What, are you answer'd yet?Some men there are love not a gaping pig;Some, that are mad if they behold a cat;And others, when the bagpipe sings i' the nose,Cannot contain their urine: for affection,Mistress of passion, sways it to the moodOf what it likes or loathes. Now, for your answer:As there is no firm reason to be render'd,Why he cannot abide a gaping pig;Why he, a harmless necessary cat;Why he, a woollen bagpipe; but of forceMust yield to such inevitable shameAs to offend, himself being offended;So can I give no reason, nor I will not,

The Christians are able to treat Shylock as they do in part because their language has separated him from the world of men. Shylock does the same here. He compares Antonio to animals that would not be valued in Jewish society: carrion, a pig, a rat. Shylock wants Antonio's pound of flesh because he no longer sees a shared humanity with him but instead sees him as a contemptible creature who impedes Shylock's values and his personal happiness. Like a rat who intrudes in his house, Antonio is a problem to be solved, not a man with whom he is called to reconcile.