Some people disparage pigs for being so eager to eat and sleep. Our langauge is full of negative expressions like "greedy as a pig", "to eat like a pig", "lazy like a pig", piggish, etc.
Eager to eat includes not only the quantity of feed, but also quality - pigs will eat nearly anything, and they'll eat as much of it as possible. That trait is so astounding that often overlook another important trait: laziness. Pigs will sleep 20 hours a day, if possible, and if woken at the wrong time, insist on going back to sleep.
Of course, the job of the pig is to eat food that we don't want and turn it into meat or fat (exactly what ratio determined primarily by the genetics), things that people really want. Voracious pigs gain weight faster, and laziness allows them to keep that weight on.
Looked at dispassionately, the job of a pig is to transform unwanted food into something we want. The very traits that we disparage pigs for are exactly the ones that pay.
Domestic pigs have been bred to be voracious eaters and particularly passive and lazy. People like Harris, writing in 1870, spoke very appreciatively of the Chinese breeds known for being very, very lazy.
Looking at ducks and geese, it is easier to appreciate the role of appetite, because they don't "eat like pigs." To produce the livers we want economically, we have to force feed them. If only ducks and geese would eat like pigs - we'd save ourselves a lot of trouble.
If you read about ducks fattening, it all sounds so complicated compared to Mangalitsa. We want birds to be a lot fatter than is natural:
Force feeding overrides animal preference and homeostasis. Although ducks may, under some conditions, voluntarily consume large amounts of food, if force feeding is interrupted they will fast for a period of 3 days or longer, indicating that ducks have been fed past the point of satiety...Mangalitsa belly or jowl is, like foie gras, a fatty and delicious product. But unlike foie gras, Mangalitsa fattening is uncomplicated. Mangalitsa pigs really want to be fat.
Increased liver weight is accompanied by a substantial overall live weight gain (in the range of 85%). Obesity influences behavior as fattened ducks are less active and exhibit increased panting in an effort to avoid over-heating. The ducks' plumage may develop a wet or greasy appearance. Anecdotal observations by members of the European Scientific Committee on Animal Health and Welfare suggest fattened ducks also demonstrate abnormalities in standing posture and gait. Mortalities have been attributed to some ducks becoming immobile and therefore unable to access water.
Hopefully one day we'll have poultry that, like pigs, naturally want to eat until they give us what we want. Or maybe we'll just culture foie gras in vitro - saving ourselves a lot of trouble. If we ever succeed in solving the poultry appetite problem, we'll see breeds of ducks disappear, just as lard-type pig breeds like the Mangalitsa disappeared in response to changing consumer preferences.