When Haven Peck tells his son that he is dying, it does not just mean that Robert is losing a person that he cares about or even a father. Haven is everything to his son Robert. Everything Robert does, he does with his father in mind. Robert is told that he will have to lose such a large part of his life that he is not sure if he will be able to go on without it. Before telling his son his secret, Haven explains his hopes and dreams. He does not want Robert to be another poor farmer like himself, and, more than anything, he never wants his son to have to slaughter a pig. Haven hopes that the education he forced on Robert son will be Robert's way out.
It would seem that earlier in the book when Haven tells Robert that his mission was to kill pigs, he was lying or at least only telling part of the truth. His mission, which becomes clear as Haven explains what he wants for his son, is to pass on everything he can to Robert so that Robert will be capable of taking over the family. At some point Haven had realized that he was not capable of bring the family out of poverty himself, and so instead he devoted himself to making sure that his boy would be able to do so. All throughout the book, Haven drops Robert little tidbits of information, not just on how to run a farm, but also about how to live and about life in general. Looking back on the text, it is obvious that he tries to get as many of these little truisms in as possible, as if he had known of his illness long before. In short, Robert is Haven's mission, not pigs.
Haven also gives Robert another grim message when he confesses that he thinks that Pinky is barren. This does not just mean that Pinky won't be able to have children, but it means that Pinky, too, will have to die one day soon. If Pinky cannot provide a little to supplement the family's income, than the cost of her food will eventually become unbearable, and she will have to become food for others. Pinky is not just a pet to Robert; she is his best friend. Knowing that he will eventually have to lose her takes all the excitement and happiness out of Robert's life.
At the end of this chapter, Robert is left in a situation where he stands to lose almost everything that he cares about within a short span of time. How he copes with the loss will be what determines whether he is really a man or not.