Foie gras from geese and ducks
(the majority of this text has been copied from the report Welfare Aspects of the Production of Foie Gras in Ducks and Geese of the Scientific Committee on Animal Health and Animal Welfare)









Many ducks and geese are being kept for the production of foie gras (fatty liver). Fatty liver production is the process of force-feeding (cramming) geese, which are normally between 9-25 weeks of age, for a period of 14-21 days. During this period the weight of the liver will increase from an initial weight of about 80g to a final weight of between 600-1 000g. Geese, along with mule ducks, and to a lesser degree Muscovy ducks, are the most popular birds used for fatty liver production. As is the case for both mule and Muscovy ducks, corn is the nutrient of choice for the force-feeding period for geese because of its high starch content and relatively low cost.

In contrast to certain other species, there is no crop in the goose and in the duck but the oesophagus can become dilated. A preparation of the animal is carried out in order to emphasise this dilation. Prior to force feeding, the bird is prepared for the various manipulations in two phases. In phase one from the third week onwards, the bird is subjected to training that is designed to dilate the oesophagus. This is achieved by grass ingestion for example. Such preparation makes it possible for the bird to receive a large quantity of food very rapidly, which will occur during the force feeding period.

In phase two, the bird is subjected to a period of rapid muscle growth. During this period, which generally lasts about four weeks, the bird receives a large quantity of food which is fed ad libitum. This results in oesophagus dilation and progressively leads to the halffatted state. The ration is distributed as a mash and is at this stage usually composed of maize 20%, wheat 53%, soya cake 19%, mineral and vitamin supplement 8%.

During this forcefeding period there is forced daily ingestion, for 12 to 15 days for ducks and 15 to 18 even 21 days for geese, of a large amount of energy-rich food. Animals receive two meals per day (ducks) or three meals per day (geese).  It is administered by force using a funnel fitted with a long tube consisting of an auger or pneumatic system that forces the maize into the oesophagus. The amount is fixed so as to ensure that the crop-like area is full. Efforts are made to avoid any tearing or splitting of the oesophagus by the movements of the tube or the amount of food inserted. Various parameters are of fundamental importance during this period. Water must be continuously available. Many farmers make the water alkaline by adding sodium bicarbonate.

To deliver the food, an auger (endless screw) is generally used. The auger is contained within the feeding tube. It is moved either by hand in traditional units or with an electric motor. With such systems, used for 30% of the birds, it takes between 45 and 60 seconds to deliver the meal. In larger units, pneumatic devices are used. They allow the farm worker to deliver the same quantity of food in 2-3 seconds. Such a system is connected through a computer which helps to determine the amount of food to deliver to each bird on the basis of the body weight and the amount of food which was delivered during the preceding meals.

Whether force feeding is to be carried out using an auger or using a pneumatic device, the bird must first be restrained and positioned by a person. In order to make catching the bird easier, the ducks or geese are either kept in groups in a small pen or cage or in a wire or plastic cage holding only one bird. Most ducks are now kept in cages of a size which does not allow the bird to turn around or stretch its wings. The head protrudes through a hole in the front of the cage roof. 20% of the ducks and all of the geese are kept in groups.

The person who will commence the force feeding grabs the neck of the bird, retrains the wings if the bird is in a pen, draws the bird towards the feeding pipe, thrusts the 20-30 cm long pipe down the throat of the bird and initiates the food pumping procedure. When food delivery is completed, the pipe is removed. In some farms the ducks or geese are kept in near darkness for all of the time except the feeding period during the 2-3 weeks of force feeding.

Several scientific reports have shown that the force feeding procedure  involve an aversive reaction. When ducks or geese are in a pen during the  force feeding procedure, they show avoidance behaviour to the person who would force feed them even though that person normally supplies them with food. At the end of the force feeding procedure, the birds are less well able to move and are usually panting but they still want to move away from the person who had force fed them.

It has also been observed that the legs of the force fed animals were pushed outwards, away from the mid-line of the body so that they met the ground considerably further than is normal and so that the leg could not be held vertically when the bird was standing or walking probably caused by the great expansion of the liver. The consequence of this was that birds with expanded livers had difficulty in standing and their natural gait and ability to walk were severely impaired.

Birds which are force fed seem to spend most of their time sitting rather than standing. The widespread use of small cages in which the birds usually cannot stand in a normal standing position makes it difficult to recognise leg problems and leg pain.

Hypertrophied livers can cause discomfort in a variety of other species. Hence it may be that some discomfort results directly from the hypertrophied liver in force fed ducks and geese. It appears that this has not been investigated. When birds are kept in small cages they are unable to exercise, preen, explore or interact socially in a normal way. It is reasonable to conclude that when birds are kept in near darkness they are likely to show impaired exploratory behaviour and hence would not be likely to exercise properly.

Birds, including ducks and geese, have a wide range of pain receptors and an elaborate pain recognition system. Most injuries caused by tissue damage during handling or tube insertion would result in pain. The oropharyngeal area is particularly sensitive and is physiologically adapted to perform a gag reflex in order to prevent fluids entering the trachea. Force feeding will have to overcome this reflex and hence the birds may initially find this distressing and injury may result.

The beak of a duck is richly innervated and the insertion of a ring through the beak would cause pain during the operation and might cause neuroma formation, and hence prolonged pain, thereafter. Similarly, most injuries to the feet caused by inadequate flooring would be painful.

Although several studies have been devoted to the technical, nutritional, histological and biochemical consequences of force feeding, very little information is available about physiological indicators of duck and goose welfare. A set of experiments has recently been carried out on the male hybrid duck (Mulard) as part of a programme instigated by INRA (Faure et al., 1996) The hypotheses tested were that force feeding could produce acute or gradually accumulating stress. Acute effects could be induced by different aspects of the process itself, e.g. the handling, the introduction of the force feeding tube, the forced introduction of the food or the excessive food quantity. Gradually accumulating effects could be due to the fact that the procedure was repeated twice a day for 14 days or to the increasing weight of the animals.

To test these hypotheses four treatments were compared on four groups of 30 ducks: control (ad libitum fed animals); extensive force feeding (i.e. introduction of the quantity of food consumed by controls); intensive (i.e. normal) force feeding and prevention of feeding. If the procedure was inducing acute stress, it could be that an increase in the corticosterone level would be observed shortly (15 min, i.e. the time required to have a maximum corticosterone secretion after ACTH injection) after the force feeding procedure.

Two types of reactions which could result from long-term problems are an increase in the heterophil/lymphocyte ratio and a variation in adrenal gland reactivity. According to species and conditions two types of changes have been described in the bibliography: a decrease of
the adrenal capability to secrete corticosterone (exhaustion) and this hypothesis was tested by injecting doses of ACTH that give a maximum corticosterone secretion; or an increase in adrenal reactivity to ACTH stimulation and this was tested with injections of ACTH that were
shown to induce about half of the maximum corticosterone secretion.

Blood corticosterone content was measured during the usual procedures associated with force feeding: catching the birds, putting them in pens, miscellaneous handling operations, insertion of the tube, food pumping procedures and the consequences of filling up the oesophagus (Guémené et al., 1996). Adrenal reactivity tests consisting of evaluating the capacity of the adrenal cortex to respond to induction with ACTH by secreting corticosterone were applied to assess the long-term effects of repeated stress. As complementary tests, creatine-kinase activities were measured together with leucocyte counts to determine the heterophil/lymphocyte ratios.

The short-term physiological effects of the force feeding operation were studied to
differentiate between the effect of tube insertion, and filling the oesophagus in birds of excess
or normal weight, in relation to control birds. None of the situations considered in the study
had any significant effect on short-term changes in blood corticosterone content, apart from
the results observed on day 7 (14th force feeding operation), in which a significant increase in
this parameter was measured in the group of over-weight force fed birds. Despite this isolated
result, the adrenal reactivity data obtained from tests carried out at the end of the force
feeding period did not show any difference and no statistically significant modification of any
of the other measures was obtained between the prior fattening period and the force feeding
period. This measure, therefore gives no evidence that intensive force feeding is stressful to
the male hybrid duck.
Finally the effect of the force feeding technique on behaviour was investigated by comparing
pneumatic equipment with traditional mechanical methods of force feeding on birds. No
difference between the two methods of force feeding could be demonstrated.
None of the measures used by Faure and his colleagues (1995-1998) indicate welfare
problems. This conclusion could be due to the fact that the adrenal responses were of a small
magnitude and that the sample sizes used were not large enough to reach statistical
significance but in most of the cases not even tendencies were observed. Adrenal responses
are sometimes masked during feeding so that all individuals which are feeding show increases
or other effects are suppressed. Destombes et al. (1997) showed that restraint of ducks in a
net immediately after force feeding induced a large increase in corticosterone levels so it is
clear that adrenal activity was far from the maximal level. However, because only the
measurement of the pituitary adrenal activity has been taken into account, no definite
38
conclusions can be drawn concerning the physiological activity of birds in response to force
feeding.
5.4 Force feeding and pathology
General questions about pathology are considered in Section 1.2.1
The questions that are addressed in this section are:
1. Is fat liver a deviation from normality?
2. Is the condition reversible?
3. Is reversibility a factor that renders the condition non pathological?
· 5.4.1 Introduction
Whilst studies of the anatomy of ducks and geese kept for foie gras production have been
carried out, the amount of evidence in the scientific literature concerning the effects of force
feeding and liver hypertrophy on injury level, on the functioning of the various biological
systems is small. In most animal production systems, such information is available so its
scarcity in relation to foie gras production is regrettable.
The available evidence which could indicate pathological effects in foie gras production are
considered in three parts. Those concerning biochemical and histological measurements are
presented in this section, those concerning more general aspects of health are in section 4 and
those concerning mortality are in section 5.
· 5.4.2 Liver structure and its biochemistry
Studies of the histological changes occurring in the liver have been described in various
publications (Baldissera Nordio et al., 1976; Bénard et al.; 1991; Bénard, 1992; Labie and
Tournut, 1970). Cellular hypertrophy has been demonstrated in both the duck and goose.
Thus the mean hepatocyte diameter in the duck increases from 7-8 μm for a non fattened liver
39
to 24-28 μm in a liver after 12 days of force feeding period. This cellular hypertrophy is the
result of an excess of hepatocytes of microvacuolar type (Bénard, 1992).
Force feeding brings about considerable modifications in the chemical composition of the
liver, increasing the percentage fat content, the protein content, and reducing the water
content (Baldissera Nordio et al., 1976; Bénard et al., 1991; Blum and Leclercq, 1973; Blum
et al., 1968; Bogin et al.,1984; Georgiev et al., 1980; Durand et al., 1968, Luret, 1987; Nir et
al., 1972). An example of the differences between the two types of liver is given in Table 2.
Table 2: Mean weight and composition of the liver from force fed and not-force fed geese
(Babile et al., 1998)
Force fed Not force fed
Liver weight (g) 982 76
Water content (%) 34.3 70.4
Protein content (%) 7.6 20.7
Lipid content (%) 55.8 6.6
· 5.4.3 Liver function
Hepatic function of force fed animals has been studied in particular to determine whether liver
function is irreversibly impaired. During force feeding, blood flow through the liver decreases
and this may affect hepatic function in various ways.
Firstly, hepatic function was evaluated using two markers, i.e. sulphobromophthalein and
indocyanine green, with high extraction coefficients (Bengone-Ndong, 1996). When these
markers were administered by intravenous route to ducks subject to force feeding, a
progressive change in the pharmacokinetic parameters of these two markers was observed i.e.
increase in the half life of elimination, area under the curve, mean residence time, etc. This
shows that the hepatic steatosis induced in ducks during force feeding results in impaired
hepatocellular function (Bengone-Ndong., 1996).
40
The consequences of force feeding were also assessed in ducks that had received
chloramphenicol by oral route. When the antibiotic was administered as the carbon 14 labelled
molecule, the plasma kinetics of the radioactivity showed that the blood concentrations were
much lower in ducks at the end of force feeding than in normally fed birds. Similarly the
residual concentrations of radioactivity, as demonstrated by quantitative whole-body
autoradiography, were much lower in force fed birds (Bengone-Ndong, 1996). When
chloramphenicol was administered in an unlabelled form, assay tests on the unchanged
product revealed that absorption of the antibiotic was delayed in time and that the plasma
concentrations were lower in force fed birds. The peak concentration occurred 2 hours after
administration in birds in the final stages of force feeding compared with a peak of 20 minutes
in normally fed birds (Mesplède, 1996). This result is clearly not because of lack of fat to
absorb the antibiotic so it is likely to be a consequence of impaired hepatic function, for
example reduced biliary secretion.
In a second phase of experiments, comparable studies were undertaken to monitor the fate of
birds which, on reaching the terminal stage of force feeding, were then returned to basic
zootechnical conditions with free access to food and drinking water. It was shown that under
such conditions the birds recovered similar body weights to those of their congeners which
had not been force fed. Similarly, plasma biochemistry studies showed a return to reference
values, obtained from birds that had not been force fed, in various parameters (cholesterol,
triglycerides, proteins and different enzymes). The return to normal took approximately four
weeks (Prehn, 1996. Plasma biochemistry studies were corroborated by a study of hepatic
histology which showed that the observed liver steatosis regressed when force feeding was
stopped so that, 4 weeks later, the hepatic cells no longer showed any sign of excess lipids.
Finally the study of hepatic function in birds subjected to a force feeding protocol showed that
the pharmacokinetic parameters following intravenous injection of sulphobromophthalein and
indocyanine green, were identical to those of birds that had not been force fed, within 28 days.
These various studies were mostly conducted in ducks but some were also carried out in
geese. The biochemical and histological measures, show that force feeding induced hepatic
steatosis in the duck or goose which was totally reversible, as demonstrated from a
41
morphometric, biochemical, histological and functional viewpoint, within four weeks (Babile
et al., 1996).
The reversibility of the consequences of force feeding was carried out in an other experiment
(Prehn, 1996). The aim of this study was to investigate the morphological and functional
changes of the liver of force fed ducks after three periods of two weeks of force feeding and
four weeks of recovery. Using the same tests as previously described, it was demonstrated
that, in these conditions, liver steatosis in force fed ducks was reversible (Prehn 1996).
These various data show that the liver steatosis obtained by force feeding induced an
impairment of hepatic function, as demonstrated from morphometric, biochemical, histological
and pharmacological points of view, but that this was completely reversible in the studies
carried out. The reversibility of steatosis which is reported above for many birds which have
been force fed does not mean that the changes in the liver are not pathological. Another
indication of how pathological the liver changes are is to consider whether the birds would die
if the steatosis which exists at the end of the force feeding period were to continue. All
producers are careful to keep good technical results and not to continue the force feeding
some extra days because if they do, very high mortality can occur. The livers of these birds
would show slightly further advanced steatosis before they died. The experimental study in
which the level of steatosis which exists at the end of force feeding is maintained for some
days has not been carried out. However, if force feeding is continued after three to four days
(Bogin et al., 1984), the level of cell damage rises significantly. This is consistent with reports
from farmers that indicate that mortality increases if feeding continues for longer than usual.
Hence it appears that the level of steatosis normally found at the end of force feeding would
not be sustainable for many of the birds. For this reason, and because normal liver function is
seriously impaired in birds with the hypertrophied liver which occurs at the end of force
feeding this level of steatosis should be considered pathological.
A further source of information concerning whether the liver is in a pathological condition at
the end of gavage is to ask qualified pathologists for their opinion on the histology of such
liver. In non-statistical surveys (Beck; 1994, 1996 unpublished) the opinions of 25
pathologists from various countries were sought on this point. Most of these considered that
42
the liver condition was pathological. Several of them pointed out that some degree of
steatosis can occur in healthy animals at certain times of life but they considered that the
degree of steatosis at the end of force feeding was much more severe than any naturally
occurring steatosis.
· 5.4.4 Hepatic steatosis of the force fed ducks and geese
Hepatic steatosis of the force fed duck or goose results from the accumulation of lipids in
hepatic parenchymal cells (hepatocytes). Among these lipids, storage cytoplasmic lipids, and
especially triglycerides, predominate. Fatty liver occurs when the hepatic production of
triglycerides is not matched by their secretion as VLDL (very low density lipoproteins) or
their degradation by beta-oxidation. This imbalance may result from a number of toxic,
nutritional or hormonal causes. The origin of hepatic steatosis in the waterfowl is nutritional.
Indeed, during force feeding, over production of triglycerides is facilitated because :
- de novo lipogenesis is mainly hepatic in avian species (Leveille et al., 1975; Saadoun and
Leclercq, 1987),
- lipogenesis is enhanced by dietary carbohydrates, which are the main component of the
maize used for force feeding (Goodridge, 1987; Saadoun and Leclercq, 1987).
The product of hepatic lipogenesis is essentially triglycerides. In the case of
overproduction, not all triglycerides can enter the secretion pathway and a large proportion
remains stored in the liver (Hermier et al., 1991). In avian fatty liver, total lipids may account
for up to 50 % of the liver weight in the goose (Fournier et al., 1997) and 60 % in the duck
(Salichon et al., 1994; Gabarrou et al., 1996). Storage lipids predominate, with 95 %
triglycerides and 1-2 % cholesteryl esters. Structural membrane lipids, such as phospholipids
and free cholesterol, account for only 1-2 and <1 %, respectively (Fournier et al., 1997;
Gabarrou et al., 1996).
Under natural conditions, some degree of hepatic steatosis occurs in the wild waterfowl, as a
consequence of energy storage before the migration. In poultry production, this specific
capacity is utilised for the production of commercial fat liver. Newly synthesised triglycerides
43
are channelled towards secretion into plasma as VLDL, or beta-oxidation. When
overproduction of triglycerides occurs, which is the case during force feeding, the liver
responds in two ways :
- the secretion of VLDL is increased, as indicated by the very high concentration of plasma
VLDL in the force fed goose compared with controls. After 14 days of force feeding, plasma
VLDL concentration is 3.31 (0.29 g/l in controls), hence it appears that the secretion pathway
is still very active and functional (Fournier et al., 1997). Indeed, force fed geese also exhibit a
dramatic extra-hepatic fattening, which indicates that accumulation of plasma VLDL results
from an increase in their secretion rather than from a defective catabolism in adipose tissues.
- the excess of triglycerides is normally stored in cytoplasmic storage vesicles. To enter the
secretion pathway, these storage triglycerides need to be partially hydrolysed and reesterified,
under hormonal influences found in the fasted state (Mooney and Lane, 1981). Since force
feeding does not allow the birds to be fasted, the liver continues to accumulate triglycerides,
until the last day, which indicates that the storage and secretion functions can still continue in
these birds.
All these data indicate that susceptibility to hepatic steatosis is a natural response of waterfowl
which is over expressed in response to force feeding. In most cases, lipid metabolism of the
liver appears to function normally.
As described above, hepatic steatosis in the waterfowl is a normal metabolic response to the
increased intake of diet carbohydrates and, in most cases, lipid metabolism of the liver appears
to function. There seems to be a low prevalence of liver lesions (0.5%) when the animals are
force fed (Bénard, 1992). If individual birds are given too much food or are fed for too long,
their individual metabolic capacity will be overloaded and dysfunctioning will occur. An
inflammatory process results in fibrosis, occlusion of the blood vessels, local liver
haemorrhages, and jaundice. However, it is strongly in the interest of the farmer to avoid this
phenomenon, because the animals suffer from the resulting diseases and because the resulting
fat liver is of no commercial value. In some cases, hepatic steatosis is associated with cell
damage, which results in an increase in the plasma concentration of hepatic enzymes (Bogin et
44
al., 1984). However, these changes are not detected in geese before the 18th days of force
feeding, whereas the maximal duration of force feeding in Europe is 15 days (Bogin et al.,
1984).
· 5.4.5 Plasma biochemistry and other measures of function
This approach has been adopted in various investigations and has shown that force feeding
produces modifications in a large number of biochemical parameters i.e. triglycerides,
cholesterol, phospholipids, fatty acids, and lipoproteins, etc....(Auvergne et al., 1988; Bénard,
1992; Blum et al., 1970; Blum and Leclercq, 1973; Blum et al., 1968; Bogin et al., 1984;
Bokori and Karsai, 1969; Braun et al., 1985; Csuska et al., 1977; Darraspen et al., 1949;
Famose, 1990; Goranov, 1979; Hudsky et al., 1974; Ivorec-Szylit and Szylit, 1969; Jouglar et
al., 1992; Labie and Tournut, 1970; De la Farge et al., 1989; Leclercq and Blum, 1975;
Losonczy et al., 1970; Luret, 1987; Nir, 1972; Nir et al., 1971; Nir et al. 1972; Nitsan et al.,
1973; Rico et al., 1983; Sevcikova et al., 1981; Szylit and Ivorec-Szylit, 1967; Szylit et al.,
1968; Timet et al., 1976; Tournut et al., 1967; Trefny et al., 1979; 1980; Villate, 1978;
Woszczyk et al., 1977; Yamani et al., 1973).
Hormone assays were performed on samples taken 4 days before force feeding began, on the
first day of force feeding, and then on days 3, 7, 14 and 17. Thyroxine, corticosterone,
testosterone, oestradiol and progesterone were assayed. The measured values of these sex
hormones did not exceed those of the thresholds of detection, but the birds were not sexually
mature. No statistically significant variation was recorded for thyroxine or corticosterone
(Famose, 1990).
It would be of interest to have the results of studies of the effects of force feeding on other
functions such as nitrogen excretion or water regulation but these do not appear to be
available. The abnormal diet that the force fed birds are kept on may have other effects on the
birds’ homeostasis. For example, if the calcium and phosphate ratios, or uptake, or
metabolism is affected in any way then the birds may become subject to some osteopathy
making their bones more fragile or even more painful. This would be consistent with birds
spending more time sitting than the non-force fed cohorts and with the high incidence of bone
45
fractures seen at the abattoir. No studies appear to have been carried out looking at calcium
and phosphate metabolism and associated hormonal imbalances.
· 5.4.6 General health indicators
It is generally observed that during force feeding, animals which are kept in groups are excited
and nervous in the first two days. Then after the fifth day, they look quiet and they move their
wings more frequently. They move when other birds move so they are generally responsive to
one another.
From a clinical point of view, there can be some signs of digestive troubles. When the working
group visited some units there was widespread evidence that faeces were more fluid than
usual. At the beginning of the force feeding period, the feathers are bright and smooth. After
some days, there can appear on some animals a change in which neck feathers become curved
and sticky. This is called "wet neck" by farmers (cou mouillé).
Some signs of inflammation of the feet can be detected on some animals at the end of the
force feeding period when they are maintained on wooden slats or on wire mesh.
In an epidemiological survey carried out in slaughter-houses, the prevalence of lesions which
are observed on carcasses and livers was investigated. 20,000 carcasses have been
systematically studied. Pathological lesions of the liver which would lead to the liver being
unusable (perihepatitis, fibrosis, local necrosis) are very rare and the prevalence is below
0.5%. They have been reviewed in several papers (e.g. Bénard, 1992).
Different lesions can be observed on carcasses. The most frequent are bone fractures. They
occur on wing bones, mainly the humerus. There is an important difference between muscovy
ducks and mulard ducks. With muscovy ducks, Bénard et al (1992) observed less than 5% of
bone fractures whereas with mulard ducks, the prevalence was between 30 and 70%. These
fractures are produced during handling of animals at the slaughter-house. It seems that
variations in the incidence of fractures can be correlated with staff care and climatic
46
conditions. In this last case, it seems that under certain meteorological conditions, animals are
more nervous and in this case, the incidence of fractures increases.
Another frequent lesion is localised on the sternum, where a necrosis of the skin can be
observed. This is observed on animals maintained in cages but it is unusual on animals kept on
the floor. The prevalence is again more important in Mulard ducks (40-70%) whereas it is
under 6% in muscovy ducks. This difference between muscovy and Mulard can be related to
the development of the pectoralis profundus major and minor muscles which are larger in
muscovy ducks.
The working group was informed that ducks at the end of the force feeding period can have
serious injuries to the oesophagus or, more usually, having clear evidence of tissue damage in
the oesophagus. It seems likely that birds have sufficient damage to oesophagus tissue, caused
by the force feeding process to have been painful to the birds. However, Levinger and Kedem
(1972) observed no alteration of the tissue of the oesophagus of force fed geese. The
prevalence of oesophageal lesions is not known at present although the industry has been
asked for this information. In a study reported by Bénard (pers comm) signs of candidosis
were observable in up to 6% of animals in each batch of birds.
The dilation of the lower part of the oesophagus which occurs in ducks which are force fed
has not been reported in non force fed ducks. It is not known whether this change is painful.
· 5.4.7 Force feeding and mortality rates
Mortality rates during the two week force feeding period were estimated from surveys in
France, Belgium and Spain.
In France a survey was carried out from 1987 to 1994 on mortality rates in force fed ducks
and geese. The mean mortality of 5,661,000 ducks was 3.4% and varied from 2.5% to 4.2%
between years. The mean mortality of 315,000 geese was 4.2% and varied from 3.5% to 5.3%
between years (Koehl and Chinzi, 1996). A recently published study (Chinzi and Koel, 1998)
gives the results of a survey conducted in 1996 on 380 farms during the whole year (about 10
batches per year and 200 ducks per batch). The survey concerns ducks housed in individual
47
cages during the force feeding period. The main aim was to detect the effects of some variable
factors (type of shed, presence of air conditioning and type of feeding device) (Table 3). The
mean “loss” observed was as high as 3.6% when the animals were fed with a mechanical
device but was limited to 1.7% when they were fed with pneumatic or hydraulic devices. No
indication of the variations between farms and batches is given for each system in the text. The
main conclusion is that the lowest mean loss rate is obtained in the most modern systems
(specific building, air-conditioning, hydraulic device). In that text the effects of the 3 factors
are presented independently but it can be expected that when the 3 factors are optimal,
mortality rate would be lower than 1.7%.
The mortality rate of 77,519 ducks on 16 production units in Belgium was obtained by
veterinary inspectors (Nicks, personal communication). The overall mortality observed was
2.75%, varying from 0 to 15% between farm and batches. It varied a lot according to the
seasons, and was higher during the summer period.
In Spain, mortality was observed during 7 years in a farm feeding from 34,000 to 55,000
ducks per year. According to the year the rate of mortality varied between 0.9 and 1.1%. It
was higher during the summer season (I. Estevez, personal communication).
These figures compare most unfavourably with mortality rates for ducks and geese during
normal rearing. No data on the mortality rate of non force fed mulards were found. However
mortality rates of muscovy ducks raised in fattening units exist (Sauveur and de Carville,
1990). The total mortality of 367,000 ducks observed during the 12 weeks before slaughtering
was 3.60%. There were two peaks of mortality, the week after hatching and the fourth week.
From the fourth week to the twelfth week the mortality decreased from 0.5% to less than
0.1% per week. Therefore for the two weeks before slaughter, the mortality rate would be
0.2% compared with 2 to 4% in the force fed mulard birds of about the same age.
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Table 3: Effects of different types of housings and force feeding systems on the losses of
mulards during the force feeding period. (Chinzi D., Koehl P.F., 1998)
BUILDING Transformed 3.1 a
Specific 2.0 b
AIR COOLING No 3.2 a
Yes 2.0 b
FORCE FEEDING Mechanical 3.6 a
SYSTEM Mechanic dose 2.4 b
Pneumatic/hydraulic 1.7 c
Transformed: Building originally for a purpose other than force feeding;
Specific: Building purpose built for force fed ducks;
Mechanical: Food delivered by auger. The force feeder adapts the amount of food to each animal;
Mechanical dose: as above but every duck receive the same amount of food;
Pneumatic/hydraulic: Pneumatic or hydraulic device, every duck receives the same amount of food.
Groups with different letters are significantly different (P<0.05)
5. 5 Conclusion
In conclusion, there is good evidence that liver structure and function that would be classified
as normal is severely altered and compromised in force fed ducks and geese, but that lipid
metabolism biochemical pathways are still functioning normally, albeit at an increased rate.
Other clinical signs that force fed birds exhibit which are not seen in age matched birds fed ad
libitum on a ‘natural’ diet include: loose faeces, wet neck, increased time spent sitting and less
time carrying out active behaviours, some aversion to the feeding process, increased incidence
of bone fractures and liver lesions at the abattoir. Continued feeding would almost certainly
result in an earlier death. Other areas of concern where there is a serious lack of data include:
mineral metabolism and corresponding hormonal homeostatic controls, examination of the
oropharynx for tissue damage, and ascertaining the adaptation times required to mitigate the
gag reflex on force feeding.
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The mortality rate in force fed birds varies from 2% to 4% in the two week force feeding
period compared with around 0.2% in comparable ducks.










European Report on the production of foie gras