I had never heard about this until today. I saw some horrific video and found numerous negative accounts of the practice.
This is cut from Wikipedia. There's lots more. Seems like a horrible practice to me.
In modern gavage-based foie gras production, force-feeding takes place for between 17 and 30 days before slaughter.
Geese and ducks show avoidance behaviour (indicating aversion) of the person who feeds them and the feeding procedure. Although an EU committee in 1998 reported seeing this aversion, they noted that at the time, there was no "conclusive" scientific evidence on the aversive nature of force-feeding. The AVMA (Animal Welfare Division) when considering foie gras production stated "The relatively new Mulard breed used in foie gras production seems to be more prone than its parent breeds to fear of people".
An EU committee in 1998 reported that there was usually clear evidence of tissue damage in the oesophagus of birds which had been gavage fed, although one 1972 study cited by the report observed no alteration of the oesophageal tissue. More recent scientific studies have shown that the esophagus of birds can be injured or inflamed by gavage feeding.
After measuring a range of physiological parameters in male Mulard ducks, it was concluded in one study that the acute stress caused by force feeding is similar at the beginning and end of the commercial production of foie gras. A similar study on Muscovy ducks found that gavage feeding was related to an increase in panting behaviour and serum corticosterone levels, indicating increased stress attributable to this feeding method.
Housing and husbandry
In France, at the end of 2015, individual cages were prohibited to improve animal welfare. They will be replaced by cages which house 4 to 5 birds.
During the force-feeding period, the birds are kept in individual cages, with wire or plastic mesh floors, or sometimes in small groups on slatted floors. Individual caging restricts movements and behaviours by preventing the birds from standing erect, turning around, or flapping their wings. Birds cannot carry out other natural waterfowl behaviours, such as bathing and swimming. Furthermore, ducks and geese are social animals and individual cages prevent such interactions.
During the force feeding period, when the birds are not being fed, they are sometimes kept in near darkness; this prevents normal investigatory behaviour and results in poor welfare.
Lesions can occur on the sternum of the birds due to necrosis of the skin. This is observed more frequently in birds reared in cages rather than on the floor. The prevalence is higher in Mulard ducks (40–70%) compared to under 6% in Muscovy ducks. This is due to the larger pectoralis profundus major and minor muscles in Muscovy ducks compared to Mulards. The relatively new Mulard breed used in foie gras production seems more prone to developing lesions in the area of the sternum when kept in small cages, and to bone breakage during transport and slaughter.
Where ducks are fattened in group pens, it has been suggested that the increased effort required to capture and restrain ducks in pens might cause them to experience more stress during force feeding. Injuries and fatalities during transport and slaughter occur in all types of poultry production, however, fattened ducks are more susceptible to conditions such as heat stress.
Foie gras production results in the bird's liver being swollen. In some species of ducks, liver size changes seasonally, increasing by as much as 30 to 50%, with more pronounced changes in females. However, foie gras production enlargens the livers up to 10 times their normal size. This impairs liver function due to obstructing blood flow, and expands the abdomen making it difficult for the birds to breathe. Death occurs if the force-feeding is continued.
The mortality rate in force-fed birds varies from 2% to 4%, compared with approximately 0.2% in age-matched, non-force-fed drakes. Mortality rates do not differ between the force-feeding period and the previous rearing phase, with both being approximately 2.5%.