Foie Gras and Animal Welfare
The fatty liver of force-fed waterfowl is the expression of a hepatic steatosis of nutritional origin, hypertrophic and reversible.
This accumulation of lipids in the liver is known as hepatic steatosis (Hermier and co., 1999).
The fatty liver contains abundant triglyceride stores (Caldwells, 2008). The ratio of fatty material to lean material is highly elevated, whereas that of the protein is decreased, the fatty overload is complete, both micro- and macro-vacuolar (Benard and co., 2005).
Foie gras is a liver for which macroscopic injuries are normally absent.
A good quality liver does not show haemorrhages, or area of necrosis, or greenish stains. The conjunctive tissue is distended but the Glisson’s Capsule remains intact (Hermier and co., 1999). When the animals are force-fed, the diameter of hepatocytes increase from 7-10 µm to 35-40 µm. The cellular structure is preserved (Benard and co., 2005).
Dr Caldwell, Director of Hepatology at the Universityof Virginia, has personally examined the histology of fatty duck liver at 12 days and 18 days of carbohydrate loading. He found no ‘disease’. The histology is consistent with simple steatosis indicating stability, reversibility and an absence of cell injury (Caldwells, 2008), it does not bear cellular degeneration or necrosis (Guéméné and co., 2007). The lipid overload affects only hepatocytes and does not seem to relate to other cellular types. There is a cellular hypertrophy during the fattening process; it does not appear to have cell hyperplasia. (Hermier and co., 1999).
Hepatic steatosis is totally reversible
At the end of a period of force feeding, if geese are reinstated to their initial rearing conditions; they spontaneously fast for several days. After 32 days, they present normalization in their blood parameters and weight; after 58 days, in their liver composition (Babilé and co., 1999). Similar observations have been reported on duck subjected to three successive rounds of force feeding and resting (Hermier and co., 1999). Their blood parameters and their liver weight return to initial state in 15 days; and their weight, in 21 days (Babilé and co., 1996). Examinations of hepatic parenchyma of animals subjected to two cycles of force-feeding/rest showed that it is strictly comparable to that of non force-fed ducks. The chemical composition of the liver presented the same order of size ratios of fatty material to lean material as non force-fed animals. (Benard and co., 2005). This hepatic steatosis is completely reversible both among geese and ducks (Guéméné and co., 2007).
The force-feeding of geese and ducks uses their natural synthesis and fat storage capacity in the liver.
Cyclical fatty liver is commonly observed in nature (Caldwells, 2008). The hepatic steatosis through force-feeding is similar to the physiological steatosis observed in birds at certain stages of life such as the start of egg-laying and migrations (Benard and co., 2005). For some species, like some fishes and some birds, the liver is the main site of fat synthesis and storage (Guéméné and co., 2007). In birds, it can explain 96% of the lipogenesis in the body (Bénard and co., 1998). In wild animals, this accumulation is a physiological adaptation to the energy needs in very particular situations. Geese ducks and other migratory birds have the natural ability to stock fat in their liver. Indeed, they do so spontaneously in order to create reserves of energy to fuel their long migratory flights. This lipid metabolism’s natural adaptation capability helps explain at the same time the intensity of force feeding hepatic steatosis and its reversibility. The force feeding exploits the maximum liver lipid storage capacity of these birds (Hermier and co., 1999).
Geese and ducks breeding were selected for their ability to produce Foie gras.
There is a genetic susceptibility to hepatic steatosis caused by force feeding accentuated by generations of selected rearing (Hermier and co., 1999).
Force feeding effect on the duck and goose liver.
The force-fed food consists essentially of a corn and water paste. It’s rich in easily assimilated carbohydrates (starch) but low in fat. This food bolsters the endogenous lipogenesis and the production of hepatic lipoproteins (Hermier and co.,1999 ).
Clinical examinations of the animals reveal a usual behaviour: mild agitation during three days, than a return to calm with an extension of the period of rest and a beating of the wings (Benard and co., 2005).
Force feeding is not perceived as a major source of stress by the waterfowls.
Stress level in birds can be gauged through the measurement of corticosterone blood level. Clinical experimentation has shown that force-feeding does not induce any significant increase in plasma corticosterone levels in ducks kept in individual cages. 2 additional experiments have demonstrated that the corticotrope system remains fully functional during the force-feeding period. In measuring corticosterone levels of ducks kept in group pens, clinical study showed no significant increase in stress levels except after the first instance of force-feeding. The Mulard duck is more sensitive to being captured, contained or handled; it explains this increase of stress level in ducks kept in group pens (Guéméné and co., 1998). A similar conclusion regarding the absence of stress perception during the force-feeding was drawn after recording the heart rate (Guéméné and co.).
Globally, force-feeding does not appear to induce pain and is not a major source of nociceptive information integrated by the nervous system (Guéméné and co.).
The absence of pain indicators results from anatomical specificity of the waterfowl involved in foie gras production.
Ducks and geese are able to swallow large preys, consequently, the inside diameter of the upper part of the esophagus, which is essentially an expandable elongated pouch in waterfowl, the pseudo-crop sac, is comparatively larger than in mammals and is not circled by cartilaginous rings. The pseudo-crop sac membrane is covered with keratin, which provides a mechanical resistance capacity. Its volume ranges from 600 to 800cm3 in mule ducks (Guy), while it is reported to be smaller in geese (below 500 cm3). For this reason, each meal with geese will have a smaller volume than with mule ducks, though the number of daily meals with geese will be higher. In addition, this pouch is located at the level of the neck (25-35cm long) allowing full expansion under the elastic skin of the neck, without any compression of the organs present in the thoracic cavity. It also allows the birds to absorb large amounts of food, which is stored there before being progressively released. Scientific studies have shown that a mule duck can ingest, spontaneously, up to 500g (over 1 pound) in a single meal and over 750g of food during a day (Guy and co., 1998). Similarly, “Landaise” Grey geese have been reported to graze 1kg of pasture daily, while also being fed a regular diet. These geese can also eat as much as 3kg of carrots daily. Force-feeding techniques used by farmers involve gradually increasing the amount of feed given to the birds. The maximum quantities of food are provided toward the end of the force-feeding period and never exceed 500g per meal (Guéméné and co.).
Another specificity resides in the fact that the opening of the trachea sits in the middle of the tongue. Thanks to the collapsing action of tongue muscles since this anatomical feature allows ducks to eat and absorb water under the water without drowning. This specificity explains why, as long as the procedure is carried under proper conditions, ducks do not have the upper respiratory tract blocked by the force fed meal (Guéméné and co.).
Panting in ducks, which frequency is increased by the end of force-feeding period, originates from a thermo-regulatory reflex. Birds have no sudoriferous glands and their capacity to eliminate extra heat through contact with the air is limited. Thus, they open their beaks and pant to eliminate the latent heat associated with water losses. Panting constitutes an effective way "to burn" excessive calories. It is neither a voluntary nor deliberate action but a reflex controlled by the respiratory bulbous centres (Guéméné and co.).
Force-fed ducks or geese do not develop any avoidance behaviour towards the force-feeder and the force-feeding context.
The behavioural responses of geese and ducks, which were previously trained to move from their rearing pen to a feeding pen in order to have access to their food, have been studied. After a training period, half of the birds were force-fed. During the experimental period, force-fed geese continued to move spontaneously and at the same speed as the control group (Guémené and co., 1998). Additional experimentation, however, demonstrated that the flight distance of ducks was higher in front of an unknown person than with the caretaker who performed force-feeding daily. The flight distance lessened with time. The familiarization limited the amplitude of the physiological responses to physical stress (Guémené and co., 2002; Servière and co., 2003), as well as behavioral reactions of fear in specific experimental tests (Guémené and co., 2002; 2006).
References:
CALDWELLS., 2008, “re: Fatty liver”, response from Dr Caldwell on hepatic steatosis.
GUEMENE D., MIRABITO L., SERVIERE J., FAURE J-L, 2007, “Rearing and Welfare of Waterfowl”
BENARD G., BENGONE T., PREHN D., DURAND S., LABIE C., BENARD P., 2005, “Contribution to the Study of the Physiology of Ducks during Force-feeding: Study of Hepatic Steatosis”
GUEMENE D., 2006, “Le nervosisme chez le canard Mulard, synthèse des acquis de la recherché et perspectives”, Septièmes Journées dela Recherchesur les Palmipèdes à Foie Gras
Anonymous, 2005, American Veterinary Medical Association (AVMA) meeting on Sunday 17th 2005
SERVIERE J.,BERNADETMD., GUY G., GUEMENE D., 2003, “Is nociception a sesory component associated to force feeding? Neurophysiological approach in the mule duck” 2nd World Waterfowl Conference Alexandria October 7-9th
GUEMENE D., FAURE J-M., GOBIN E. GARREAU-MILLS M., DOUSSAN I., GOURA P., GUY G., 2002, “Effet de la familiarisation à l’homme sur les réponses comportementales de peur chez le canard mulard” Cinquièmes Journées dela Recherchesur les Palmipèdes à Foie Gras
HERMIER D., SALICHON M. R., GUY G., PERESSON R., MOUROT J., LAGARRIGUE S., 1999, “Hepatic steatosis in force-fed waterfowl: metabolic bases and genetic
Sensitivity”, INRA Productions Animales, 12, 265-271
BABILE R., AUVERGNE A., DUBOIS J-P, BENARD G., MANSE H., 1999, “Réversibilité de la stéatose hépatique chez l’oie”, INRA Productions Animales., 12, 265-271
BENARD G., LABIE Ch., 1998, “Evolution histologique du foie des palmipèdes au cours du gavage”, Troisièmes Journées dela Recherchesur les Palmipèdes à Foie Gras
GUEMENE D., GUY G., DESTOMBES N., GARREAU-MILLS M., FAURE J-M., 1998, “Aptitude physiologique du canard Mulard male à répondre à un stress aigu pendant la période de gavage”, Troisièmes Journées dela Recherchesur les Palmipèdes à Foie Gras
GUEMENE D., GUY G., SAMSON M., GOURAUD P., GARREAU-MILLS M., FAURE J.M., 1998, “Réponses physiologiques et comportementales de l'oie à l'acte de gavage”, Troisièmes Journées dela Recherchesur les Palmipèdes à Foie Gras
GUY G. FAURE J-M, GUEMENE D., 1998, “Capacité d’ingestion chez le canard Mulard Male”, Troisièmes Journées dela Recherchesur les Palmipèdes à Foie Gras
BABILE R., AUVERGNE A, ANDRADE V., HERAUT F., BENARD G., BOUILLIER-OUDOT M., MANSE H., 1996, “Réversibilité de la stéatose hépatique chez le canard Mulard”, Deuxièmes Journées dela Recherchesur les Palmipèdes à Foie Gras
GUEMENE D., GUY G., SERVIERE J., FAURE J-M., “Force feeding : An Examination of Available Scientifique Evidence”
