It's pure unadulterated farmer-think. It makes perfect sense if you think like a dairy farmer. In his twisted suicidally depressed thinking, he knew they would suffer very much after his death. And he's absolutely right.
Heavy milkers that go unmilked for even 12 hours will swell up with milk and engorge. Then comes mastitis, sepsis and a slow nasty death. By the time people figured out what to DO after he died, with these cows, for many of them it would be too late. Their udders would be so engorged they may not be able to be milked. These are genetically "engineered" to be heavy milkers, perhaps 13 gallons of milk a day. Abrupt cessation of milking is deadly to these critters.
And a milk cow who loses her milk is useless. Who would take them? How many cow rescues are there for retired and probably sickened, suffering cows?
He was thinking clearly. About everything except his own life, that is