Controlling population and preventing the spread of disease is a major challenge for very large hog farms.
Breeding sows will spend most of their lives living in farrowing crates. These are small pens just barely large enough to hold an adult sow. They live in these crates either pregnant or nursing piglets until they are too old to produce. Care must be taken to arrange the farrowing crate in such a way as to allow the piglets room so that the mother will not crush them when she lays down to nurse.
When populations grow too high to be sustainable some of the piglets are aborted in order to keep the population at a sustainable level. These aborted fetuses are sometimes sold for various purposes including being sold to schools for dissection.
In recent years the explosion of PEDV (porcine epidemic diarrhea virus) in American farms has lead to massive control measures. PEDV is not fatal to adult pigs but it is very lethal to small piglets. If a mother sow is infected with PEDV it will pass the virus on to the piglet and the piglet is very unlikely to survive. PEDV is passed through solid waste and is very contagious, especially in the conditions in large farms where pigs cannot escape their waste. There is a vaccine for PEDV but it is not very effective against the strain currently spreading across the United States.
One course of action that can be taken in extreme cases is to cull all of the fetuses once PEDV is confirmed. Then the infected sows are removed, the barns disinfected, and new sows are brought into the farrowing barns. The culled fetuses are not suitable for sale and are collected in one place, (in this case a large dumpster) and then burned or buried.
It should be noted that PEDV has also infected hogs that don’t live in confinement farms, though the spread of the virus is more difficult as the animals aren’t constantly exposed to the infected waste.