The key to how much an animal can suffer is its sentience, namely its
ability to feel pain, to be conscious of what it is feeling, and
possibly also remember what it has experienced. To some extent this
can be modulated by intelligence, however, the capacity to experience
pain and distress is not directly linked to intelligence. In fact, it
is also possible to argue that intelligence can help mitigate pain and
distress. For examples, a human can find suffering more bearable if
it arises from an activity done to cure or prevent a condition that
would cause greater suffering in that individual, or even if it is due
to an altruistic act to help another, especially someone in a close
emotional relationship to the individual.
Unfortunately, as shown in some of the extracts given below, the
general view seems to be that it is not possible to define a measure
of intelligence that will permit comparisons to be made across all
animal species. Our own perceptions of different species can cause us
to rank them in specific ways. However, as also shown by examples
given below, sheep, pigs, cows and chickens all display behavior and a
capacity for memory that can be seen as a reflection of a certain
degree of intellectual ability.
Welfare issues arise in how the animals are kept, how and how long
they are transported, and how they are finally killed.
One organization that exists specifically to consider these issues is
Compassion in World Farming, so I took a look at its web site. Here
you will find a 44-page report, published only this year, which
contains many references to the academic literature and has the title
Stop - Look - Listen: Recognising the Sentience of Farm Animals (Nb
this is in pdf format, and a bit slow to download because it contains
many photographs, file size c. 2.5 Mb)
CIWF has also produced many other reports covering various welfare
aspects in the farming of different livestock species. Links to all
of these are at:
CIWF has also established a web site dedicated to the question of
animal sentience at
The notes that follow are taken from the CIWF reports, and from other
sources and my own knowledge (I work as a scientist in another area of
animal welfare, but am also familiar with some of the work on farm
1. Sentience and intelligence
There's no way to scientifically prove animal intelligence, but Steve
Davis is sure animals on the farm have minds and can think
. In a
paper presented at the annual meeting of the American Society of
Animal Science, Davis reported that more than 80 percent of those he
surveyed believed animals have minds and can think
. The faculty and
students surveyed gave the highest marks to their pets. They ranked
the dog and cat as most intelligent with the pig and horse close
behind. Next came the cow and sheep. Last, in a dead heat, were the
chicken and turkey
. Respondents were asked to assign a number to the
different species with 1 being highest intelligence and 5 being the
lowest. Overall, dogs earned a 2.1 ranking and cats 2.3. The pig and
horse were tied at 2.6
. The animal science faculty and students and
veterinary medicine faculty rated the cat and pig even. Philosophy
faculty rated the pig smarter than the cat
Ranked at the bottom in
perceived intelligence were the cow (3.2), the sheep (3.5), and the
chicken and turkey (both at 4.0)
. He said scientists have been
unsuccessful in measuring absolute animal intelligence. "Behavioral
scientists may say every animal is smartest for its own ecological
niche," he explained. "The limitation in measuring cross-species
intelligence is the inadequate tools for assessment we have available.
Standard methods of assessment may show one species to be smarter on
one test than another species, but a different method might show just
From Oregons Agricultural Progress magazine, Fall, 1997
It is thus that to pass an intelligence test in a behavioural
laboratory, animals are still required to master singularly human
skills. Out in its own domain however, the animal is often more than a
match for the human being in terms of observation, cunning, conscious
deliberation and other survival skills
But if intelligence means
different things to different people, just consider what it might mean
to the animal kingdom as a whole with its mind-blowing diversity. Out
in their own environment, animals must use their cunning and
intelligence to survive. And as if each species inhabits a separate
reality, intelligence is unique in form to each and then varies widely
again with the individual. The skills they demonstrate are similarly
unique, with certain animals displaying everything from abstract
thought to complex communication abilities.
From: The Rose-tinted Menagerie
Although intelligence is a difficult term to define, as applied to
humans the finding of consistent rank-ordering on problem-solving
tasks serves as a useful working definition of intelligence
literature on animal intelligence defined as the study of individual
differences in problem-solving tasks though relatively meager
compared to the extensive human literature, yields a very different
conclusion. The accepted view is that there is no consistent
rank-ordering to animals performance across problem-solving tasks.
One scientist went so far as to argue that there are no grounds for
speaking of rat or mouse intelligence. Neither are there reasons to
expect that experimental results obtained with one piece of apparatus
will generalize to another task . . .. (Wahlsten, 1978, p. 89).
Another scientist echoed a similar view in noting that "one cannot
speak of intelligence within a species of animals. No one has found
evidence in support of a general level or capacity that result in an
animal . . . consistently performing above or below the level attained
by other members of the species on several different tasks (Warren,
1977, p. 41-42).
(Comparative Intelligence Lab, College of the Holy Cross, Worcester,
It's difficult to get a consensus on which is the smartest animal.
Researchers don't like to label any species, including homo sapiens,
the brain or bozo of the natural world. "Intelligence" is too hard to
quantify, even in people, so scientists prefer to rate animals'
specific cognitive abilities
"Pigs are really good at remembering
food sites," says Held, "because in their natural environment food is
patchily distributed and it pays to revisit profitable food patches."
From What Flipper, Wilbur and Koko know by Tamar Simon
Pigs are actually more intelligent than any breed of dog. Like dogs,
piglets learn their names by two to three weeks of age and respond
when called. They are also very discriminating eaters, and are
particular about their living space. Pigs enjoy novelty and are
extremely active and inquisitive.
From A Closer Look at Pigs (Humane Society of the US)
Darwin said that humans and the higher animals have the same
senses, intuitions and sensations, similar passions, affections and
the same faculties of imitation, choice, imagination, the
association of ideas and reason though in very different degrees (C
Darwin The Descent of Man and Selection in Relation to Sex, 1871).
From Stop - Look Listen (CIWF web site)
Sentience does not necessarily mean that animals have complex
abilities to understand, to learn, to solve problems or to be
But intellectual abilities must give us a strong
indication that the animal is consciously aware and has subjective
experiences. One strong indicator of animals sentience is their
ability to distinguish and choose between different objects, animals
and situations, which shows that they understand what is going on in
their environment. Another strong indicator
is animals ability to
learn from experience, to use their experience to cope with the world
more effectively (from their point of view) and to respond flexibly to
new situations that confront them.
The ability to recognise and remember can be considered to be a
reflection of one type of intellectual capacity. Cows are thought to
be able to recognise 50-70 other individual cows, and can also
recognise humans. Pigs are thought to be able to recognise up to 20-30
other individual pigs. Sheep have been shown to remember up to 50
individual sheep faces for as long as 2 years. I was at a meeting
where this work was presented by Dr Francoise Wermesfelder, and she
also showed results which indicated that sheep could remember up to
about 10 individual human faces. Hens were found to be efficient at
distinguishing between and remembering 2 individual humans. They
ignored the human who did not bring them food, while turning to the
one who did. Hens and pigs have been shown to learn from each other.
Chickens, sheep, pigs and cows can all demonstrate a capacity for
problem-solving in the right circumstances. Cows, pigs, sheep and
chickens have also been found to have sophisticated communication
systems with a large number of different calls and postures.
Communication is yet another sign of intelligence.
Pigs and chickens are more intelligent than most people believe
Chickens can learn from each other and are encouraged by example, and
pigs use subtle social behavior and signal their competitive strength
Despite their reputation as the bird-brains of the avian
world, chickens can be taught what food to eat or avoid, are able to
adapt their behavior and can learn to navigate
There are hidden
depths to chickens," said Professor Christine Nichol who has studied
. "Our results suggest that pigs can develop quite
sophisticated social competitive behavior, similar to that seen in
some primate species," Dr Mike Mendl told the British Association for
the Advancement of Science festival. A better understanding of animal
intelligence could help farmers tackle problems such as aggression in
pigs, which causes deaths and injuries and accounts for an estimated
$30 million each year in lost revenue in Britain, according to Mendl.
From Farm Animals Not So Dumb CBS news item, Sept 11, 2002
From Stop Look Listen
Pigs are generally recognised to be at least as good at
problem-solving as dogs, and can remember where to find hidden food.
But they also seem to have an understanding of what is going on in
other pigs minds and make their own decisions accordingly in order to
get what they want. This type of thinking has often been assumed to
be special to apes and humans. Bristol University scientists have that
if one pig has been taught where food is hidden, other pigs notice
that the pig is informed and follow the leader rather than searching
randomly. They then steal the food from the informed pig. In
response, the informed pig avoids going directly to the food when
the non-informed pig is near, in order to have time to eat some food
before the other pig arrives.
2. Pain and its perception
With respect to the perception of pain, all vertebrates have more or
less the same physiological and neurological mechanisms for becoming
aware of and responding to painful stimuli. The nervous systems of
birds are as complex as those of mammals, and fish show the same
physiological responses to painful stimuli as seen in humans.
Therefore, it is reasonable to assume that vertebrates at least can
feel pain, and some scientists are now trying to determine whether
this is also the case for invertebrates.
One of the problems with trying to assess pain is that there is no
objective way in which to measure it. Even humans, with their capacity
for language, cannot really express the degree of pain they feel, and
will vary in the extent to which they can tolerate pain. The behavior
of an animal will give clues about whether it is experiencing pain.
For example, it might squeal or cry, try to protect and avoid using an
injured leg, try to keep away from a painful stimulus, show mood
changes (for example becoming unresponsive). According to Stop -
Look Listen (CIWF web site), Experiments have shown that the pain
perception thresholds are broadly similar for horses, cattle, sheep
and humans. However, A sheep is much less likely to show obvious
signs of pain than a domestic dog, probably because sheep are a
species that is preyed on and signs of weakness attract predators.
The Stop - Look Listen report gives examples of events where we can
assume that animals feel pain. For example, piglets that are being
castrated without anaesthetic squeal more loudly than other pigs that
are not experiencing this procedure. Tail docking causes plasma levels
of cortisol to rise in lambs. Cortisol is a hormone produced in
situtations of stress and changes in its levels are used as a measure
of acute distress. Debeaked hens will avoid using what is left of
their beak except when they have to use it for feeding, and broiler
chickens that are lame will chose food containing an analgesic drug in
preference to food without it.
3. Fear, anxiety and distress
The presence or absence of pain is only one factor that affects an
animals welfare. Fear and anxiety are also relevant. Again, these can
be measured physiologically, eg by measuring levels of stress
hormones, and also by observing behavior. Examples include: Piglets
make distinctive, frequent squeals when they are separated from their
mother and some of them eventually become apathetic, as if they have
given up on life. Sheep show an increased heart rate when they cannot
see other sheep, and it increases even more when they see a man with a
dog. Pigs, calves and cows that have been mistreated try to keep away
from humans. Pigs can experience so much stress from being put in with
other, unfamiliar, pigs and/or from rough handling by humans that they
collapse and die. Cows express very obvious signs of distress when
they are separated from their calves.
If an animal is prevented from carrying out behavior that is normal to
its species, for example foraging or nesting, it can also suffer
stress as a result. Such stress has been shown in cows prevented from
eating grass they could see, chickens denied food or given a very
restricted diet, boars that were deliberately made to experience
sexual frustration and pigs forced to give birth in a small farrowing
crate with no room to build a nest.
Foraging and pecking can occupy 50- 90% of the time of a free range
chicken. In battery farm conditions, this impulse is transformed into
a harmful pecking of other chickens. Pigs have been demonstrated to
have a distinct preference for a floor covered with straw, rather than
bare concrete, while peat and mushroom compost were even more popular,
because they allowed for better rooting and foraging. Crates for veal
calves are typically 61-76cm wide, giving a floor area of around 1m2
and no possibility of free movement. Veal crate calves are also fed a
diet deficient in iron and are raised in the dark, so as to keep the
meat as white as possible.
The fact that animals clearly enjoy playing is a hallmark of their
complex mental life, and involves the ability to understand anothers
mood, to cooperate and to pretend (Stop - Look Listen (CIWF web
The social behavior of animals can be complex. Cows show stress when
separated from the herd. Free-range pigs stay in small groups and have
defined territories. They make communal nests for the group. Chickens
have complex social hierarchies that have been extensively studied.
Family bonds are a further level of social life. Both hens and pigs,
if kept free-range or in the wild, will show complicated nesting
behavior, often travelling some distance to find a suitable place.
Pigs and cows show distress when separated from their young. Cows
have been known to maintain mother-daughter relationships throughout
life if allowed to stay in a family group.
4. Human attitudes to the concept of sentience in animals:
The theories of Descartes (1596-1650) became dominant among scientists
until the latter half of the 19th century. Descartes considered
animals to be incapable of thinking and being conscious of self, and
therefore incapable also of feeling. He considered that if an animal
squirmed and tried to avoid a source of pain, squealed or cried, these
were simply automatic reflexes and not signs that the animal actually
felt pain or distress.
A number of eminent thinkers disagreed with Descartes. For example,
Jeremy Bentham (1748-1832), a philosopher who was also active for
legal and social reform made an often-quoted statement in his book
Introduction to the Principles of Morals and Legislation. He
pointed out that an animal may be fully capable of experiencing
suffering even if its intellectual abilities are deemed to be low, and
he said The question is not, Can they reason? nor Can they talk? but
Can they suffer?
Gradually, new ideas began to take precedence, although it took
scientists a while to feel able to admit the notion of animals being
conscious beings. Before, a scientist who did this would become a
laughing stock and not be taken seriously by his peers. Even now,
many scientists fear being labelled as anthropomorphic in their
attitude to animals. However, most people do now consider animals to
have a capacity for thought and a consciousness of themselves.
However, while it is now generally accepted that animals have a
greater or lesser degree of consciousness, we can be very inconsistent
in our attitudes. You might remember a recent protest directed at
Korea, which reflects the upset felt by Westerners about the fact that
some Eastern people eat dogs, although Westerners will eat equally
sentient and intelligent cows with no compunction. Likewise, the
English get unhappy that the French eat horses, yet will attack a pork
chop with equal gusto as the French. The type of work someone does can
also influence the extent to which they are able or willing to admit
to animal sentience, for example, scientists who experiment on
animals, livestock farmers, slaughterhouse workers, can become
desensitized to these issues, probably as a form of emotional
5. Welfare problems in farming
Commercial, intensive farming aims to get the maximum value out of an
animal in the minimum time. This involves a total control over the
animals lives, in terms of their accommodation, diet, contact with
other animals and mating. Often this leads to a total deprivation of
the possibility for the animals to follow their instinctive behavior
pattern. This causes frustration and stress. The conditions in which
animals are kept in intensive farming can also be a source of fear and
of physical discomfort and pain. Practices such as tail docking,
debeaking and castration are a further source of pain. Long periods of
transport in very confined conditions, with insufficient food, water
or temperature control also cause distress and physical injury. The
last moments of an animals life in the slaughter house are also
filled with fear and stress and often with pain as well.
a. Broiler chickens
CIWF has the following reports at the URL given above.
The Welfare of Broiler Chickens, 2000
Most of the welfare problems arise from selective breeding for faster
growth and more efficient food conversion. Broiler chickens have a
mortality rate of 1% a week, 7 times the rate of laying hens of
the same age. In one heavy strain of broilers, over 47% have been
found to have dyschondroplasia, a disorder of bone growth, in their
legs. A 1999 survey in Denmark found development of dyschondroplasia
in 57% of chicks. However, the broiler industry does give see
lameness as a priority problem to be resolved. Broiler chickens
hearts and lungs often
cannot keep up with their bodies fast growth rate. They frequently
suffer from heart failure when they are only a few weeks old. High
stocking density leads to increases in leg problems, breast blisters,
chronic dermatitis, hock burns and infections. Crowded sheds lead to
wet litter, increased air pollution from ammonia and dust particles
and worse temperature and humidity control, all of which damage the
broilers health and welfare. Broilers that are allowed to grow to
adulthood to be used for breeding are restricted to between one
quarter and one half of the amount of food they want to eat during
their growing period and appear to be chronically hungry, frustrated
LAMENESS OR LEG WEAKNESS PROBLEMS IN BROILER CHICKENS A RESUMÉ OF THE
LATEST SCIENTIFIC RESEARCH
A major cause of leg problems lies in the fact that the modern
broiler reaches its slaughter weight in just 41/42 days. This is twice
as fast as 30/35 years ago. These accelerated growth rates have been
achieved by selective breeding, together with rich diets and
growth-promoting antibiotics. The problem is that what grows quickly
is the muscle, which is what is eaten as meat. The bones of the legs,
however, fail to keep pace with the rapid body growth and so cannot
support the overdeveloped body. As a result, many broilers suffer from
painful leg disorders.
In one study, 2% of the birds were incapable of sustained walking and
could only move with the help of their wings or by crawling on their
As already mentioned above, the fact that lame birds prefer food
containing an analgesic drug shows that they are in chronic pain.
Chicken How Come Its So Cheap?
From the hatchery, the birds are taken to the farm where they are
packed into huge windowless sheds which can hold 30-40,000 chickens.
As the birds grow bigger, conditions deteriorate and the sheds become
so overcrowded that one can barely see the floor, so thickly is it
carpeted with chickens.
In many broiler sheds an unbelievable 19 chickens or more are
crammed into each square metre of floor space.
Due to lameness and overcrowding, many broilers spend a
disproportionate amount of time squatting on the litter (usually
woodshavings) which covers the floor. All too often it is damp and
dirty. Prolonged contact with such litter leads to many broilers
suffering from painful breast blisters, hock burns and ulcerated
When the time comes for the birds to be transported to the
slaughterhouse, teams of catchers depopulate the sheds at great
speed often carrying 4 or 5 birds upside down in each hand. The
chickens are held by just one leg, with rough, even brutal handling
being commonplace. Catching in this way leads to dislocated hips in
some broilers. This is associated with profuse haemorrhaging; in the
worst cases, the femur (thigh-bone) can actually be forced into the
birds abdominal cavity
The report states that in the UK alone, over one million chickens die
each year while being transported to the slaughterhouse. Once there,
The birds are hung upside down from shackles. Having their legs
squashed into the metal shackles is painful. The shackles are on a
moving line which takes the terrified birds to an electrified
waterbath, through which their heads are dragged. This is designed to
stun them into unconsciousness. From there the line takes them to the
automatic neck-cutting blade. Many birds are not properly stunned and
recover consciousness before or after neckcutting
. . Some birds are
still alive when they are plunged into the scalding tank (designed to
loosen feathers prior to plucking).
Saving Their Bacon
Sow stalls are so narrow that the sow cannot even turn round. She is
confined in the metal-barred stall on a hard concrete floor throughout
her 161/2 -week pregnancy. And for pregnancy after pregnancy. In
short, for most of her adult life..
Even the floor is an uncomfortable combination of concrete and slats.
No bedding material is usually provided.
caged sows are more likely to suffer foot injuries, lameness, and
long-term pain from infected cuts and abrasions. Lack of exercise
leads to weakened bones and muscles. Being unable to move freely also
causes greater levels of urinary infections. Heart problems, too, can
Caged sows commonly carry out meaningless, repetitive motions - such
as bar biting - known as stereotypies. Experts regard these
stereotypies as outward signs that the animals are under stress and
Piglets are often separated from their mothers at an early age and
reared in conditions that are barren and overcrowded. On many
intensive pig farms, young pigs being fattened for slaughter are
forced to spend their lives on bare concrete or slatted floors. There
is normally no bedding material.
Bored and frustrated in these barren conditions, the pigs sometimes
turn to the only other thing in their world: the tails of other
pigs. They begin to bite those tails. Scientific evidence shows that
the right way to prevent tail-biting is to keep the pigs in good
conditions. What factory farmers do is to slice off part of the tail
with pliers or a hot docking iron without the use of anaesthetic.
c Transport and welfare
Live Exports: A Cruel and Archaic Trade
Many of the lambs that are born at Easter and that we enjoy seeing in
the fields and on the hills are, when just a few months old, packed
off to continental abattoirs. First, they are trucked to a market,
which are stressful, even frightening places for animals, being full
of unfamiliar noises, smells and people. Often they have to stand for
hours on end in pens so overcrowded that they cannot lie down. Usually
they are given no water which on hot summer days can lead to severe
thirst, even dehydration. Rough handling is commonplace. Finally, they
are herded back on to a truck
Crammed into overcrowded trucks, the
animals are sometimes given neither food nor water even during
journeys of 30 or 40 hours or more
. A major research paper by Bristol
University scientists has confirmed that vulnerability to heat stress
is of primary concern in the transport of sheep.
Evidence from the literature suggests that young calves are not well
adapted to cope with transport and marketing, often suffering
relatively high rates of morbidity and mortality, both during, and in
the few weeks immediately following transport ..... Comparatively few
normal calves actually die during transport but they succumb, usually
within four weeks, to secondary disease as a consequence of their
inability to respond appropriately to transport.
The scientific evidence shows that pigs are particularly poor
travellers. They are especially vulnerable to travel sickness
vomiting and can begin to suffer from dehydration after just 8
d. Slaughter of pigs, cattle and sheep
Animal Welfare Problems in UK Slaughterhouses
Slaughter is traditionally a two stage process: stunning followed by
The survey found that, in the abattoirs which did not restrain pigs
for stunning, over 1 in 3 pigs (36%) were stunned in the wrong
position, i.e. the tong placement did not span the brain
15.6% of the
pigs which were not restrained at stunning had to be re-stunned
number of pigs (2.3%) in abattoirs not restraining pigs at the time of
stunning had to be restuck due to inadequate sticking
. they found
that, in abattoirs not restraining pigs at stunning, 20.5% of the pigs
were exhibiting rhythmic breathing, and thus were possibly recovering
from the stun, at the time of sticking.
Gregory & Wotton (1984) found that where both carotid arteries in
sheep are severed, sticking takes an average of 14 seconds to induce
loss of brain responsiveness. They found, however, that this interval
was 5 times longer 70 seconds where only one carotid artery is
severed. Where neither carotid is severed, it can take up to 5 minutes
to induce loss of brain responsiveness.
This survey found that 6.6% of cattle showed evidence of being less
than fully effectively stunned.
. In 2.6% of cases the shot was so
poorly applied that the animal had to be stunned a second time, with
0.2% requiring a third stun.
CIWF Trust is firmly opposed to the carbon dioxide stunning/killing
of pigs and believes this method should be prohibited. Before the pigs
become unconscious they can suffer from breathlessness and
hyperventilation. Raj & Gregory (1996) concluded that pigs show
profound aversion to a high concentration of carbon dioxide and that
this gas leads to severe respiratory distress. CIWF Trust believes
that the use of carbon dioxide gas is an inhumane way of
A further welfare problem arises with religious slaughter (Jewish and
Muslim) of cattle, sheep and chickens, since this forbids the initial
stunning. It is considered by animal experts to result in very high
levels of fear and distress during the last minutes of life.
The Welfare of Pigs, Cattle & Sheep at Slaughter
A major welfare problem has been highlighted by a recent study which
shows that calves can take a much longer time than other species to
lose their brain function following neck sticking (Anil et al, 1992).
As a result some calves show clear signs of recovery after sticking.
responsiveness can be present in the brains of calves for as long as
104 seconds after neck sticking. Moreover, it must be remembered that
the average period of unconsciousness induced in calves by electrical
stunning is a mere 18 seconds. When these two figures are considered
together it is clear that a very large percentage of electrically
stunned calves may resume consciousness during bleeding out.
The survey points out that the cortisol level in the blood (an index
of stress) taken at sticking averaged 67.6 nmol/litre for the animals
stunned while standing free, whereas the mean for the head restrained
animals was 143.1 nmol/litre. The survey concluded that the "enforced
usage of this type of head restrainer could be a cause of distress to
the cattle involved".
Search strategy: My own work relates to other areas of animal welfare,
but I am reasonably familiar with general welfare issues and the
organizations that deal with them. I went to the CIWF site, because I
already knew of it and knew this was the obvious place to start.
Additional Google searches on: 1. animals intelligence, 2. farm
animals intelligence, 3. comparative intelligence animals