A scientific project of unprecedented scale, involving almost all research into the welfare of laying hens


What does a caged hen experience? How does it differ from a free-range hen? What is the nature and extent of these differences? While it is now possible to precisely compare the carbon footprint of different foods, the "animal suffering" footprint remains unclear.


The Welfare Footprint Institute aims to fill this gap by quantifying for the very first time the animal suffering behind a food product: the egg.


These results are the result of extensive work between 2021 and 2025, bringing together specialists in animal welfare and veterinary sciences, ethology, and neuroscience, who analyzed more than 1,000 studies. This interdisciplinary work resulted in a pioneering methodology for quantifying animal suffering throughout the egg production cycle.

Scientist

Cynthia Schuck Paim

Cynthia holds a PhD in Zoology (Animal Behavior and Intelligence) from the University of Oxford. She has collaborated with research institutions in the UK, USA and Brazil, and has written over 70 scientific publications, book chapters, and educational materials.

(list here)
Scientist

Wladimir J. Alonso

Wladimir holds a PhD in epidemiology from the University of Oxford, with over 20 years of research experience in evolution, ethology, and global health. He has collaborated with universities worldwide and published over 100 studies in peer-reviewed journals.

(list here)

1.A 3-STEP METHOD FOR QUANTIFYING ANIMAL SUFFERING

1

The steps of quantifying suffering

  • 40%

    chickens suffering from keel fracture

  • 100%

    caged hens victims of restricted freedom of movement

  • 5,5%

    chickens with skin lesions

  • + 122 other sources of pain

2

Quantify the suffering caused by each affliction

Breastbone fracture

2min of agony

45h of pain

5h of suffering

80h of discomfort

Restriction of freedom of movement

2min of agony

45h of pain

5h of suffering

80h of discomfort

Skin lesions

2min of agony

45h of pain

5h of suffering

80h of discomfort

+ 122 other sources of pain

3

synthesize the two previous steps to calculate the average suffering per hen over its lifetime

Breastbone fracture

33% hens undergoing

2min of agony

45h of pain

5h of suffering

80h of discomfort

+

Movement restriction

100% hens undergoing

1min of agony

45h of pain

5h of suffering

30h of discomfort

+

Skin lesions

48% hens undergoing

1min of agony

5h of pain

4min of suffering

30h of discomfort

+

the same for the other 127 afflictions

=

During its lifetime, a caged hen undergoes on average:

6 minutes of agony

385 hours of pain

448 hours of suffering

3000 hours of discomfort

Suffering Scale

The researchers defined four levels of suffering using behavioral and functional criteria: Is the hen still carrying out its usual activities (eating, exploring, playing)? Is it able to concentrate and react to its surroundings? Are physiological signals associated with discomfort or stress observable? How does it show its suffering (vocalizations, agitation)? Is pain medication helping it ?

Discomfort

Mild discomfort, without impact on behavior. Comparable to an itch or slightly rubbing shoes.

Criteria : preserved attention span, absence of behavioral and physiological signs.

Pain

Persistent pain, altering behavior without completely preventing it. Comparable to a headache or chronic back pain.

Criteria : decrease in pleasant activities, mild cognitive impairment, effectiveness of analgesics.

Intense Suffering

Constant pain, taking priority over everything else. Reduces activity, well-being, and attention. Comparable to a migraine or fracture.

Criteria : drastic change in activity, environmental unresponsiveness, need for strong medications.

Agony

Extreme, unbearable pain even for a short time. Causes screaming, trembling. Comparable to unbearable suffering.

Criteria : intense behavioral expressions, conduct dangerous to bodily integrity, inability to conceal.

2.THE METHOD IN DETAIL

2.1 List all sources of pain for chickens

What do chickens suffer from?

An in-depth review of the scientific literature was conducted to identify the main sources of pain for chickens in livestock production, and how frequently they occur depending on the farming method. These can be physical pain (fractures, skin injuries, infections, etc.) or psychological pain (fear, restricted behavioral needs, etc.). In total, xx sources of pain were identified and studied by the Welfare Footprint Institute, based on a study of yy articles.

Some psychological pain

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Restriction of freedom of movement :

Locked in cages, chickens can hardly stand, clean themselves, turn around or stretch their wings.

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Nest deprivation :

Cages do not provide a suitable nesting site, while several studies have shown that hens search for a nest at all costs before laying.

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Behavioral deprivation :

Unable to peck at the ground in search of food (a strong need for them), chickens become frustrated and attack each other. Their beaks are cut to prevent this risk.

Some physical pain

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Breastbone fracture :

Bone fractures are very common in livestock farming and cause significant suffering for chickens.

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Peritonitis :

A disease that occurs when egg yolk leaks into the hen's stomach, causing painful inflammation that can become infected and fatal.

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Tissue damage and feather loss :

Attacks between hens caused by frustration result in feather plucking, skin damage, and vent damage.

List of all sources of pain

breastbone fracture

egg peritonitis

restriction of nesting possibilities

Feather plucking

2.2 Quantify suffering for each source of pain

How much pain does a breastbone fracture cause? A skin lesion? The inability to implantation lead to?

This is the heart of the method: for each source of pain, it is necessary to determine how much suffering results for the hen.

The Pain-Track is a tool that allows this quantification. The four levels of pain are represented on the vertical axis and the different time phases on the horizontal axis.

For each phase, scientists rely on various indices (behavioral, pharmacological, physiological, etc.) to determine the corresponding level of suffering.

In total, more than 70 specialists in animal welfare and veterinary sciences, ethology and neuroscience collaborated to establish all the pain tracks.

Pain-track of a skin lesion

Pain-track of a skin lesion
Scientist analyzes traces of pain

Listing the pain of caged animals allows us to better understand their suffering in order to improve their living conditions and promote more ethical breeding practices.

access all the pain-tracks

2.3 Calculating the overall suffering of a farmed hen

How can we combine fractures, infections, stress... etc., to obtain a single measure of suffering?

The previous steps have allowed us to understand the sources of pain for the hens, their frequency and the amount of suffering associated with each.

It remains to add up all these results to determine the overall suffering undergone by a hen.

Breastbone fracture

40% hens undergoing

2min of agony

45h of pain

5h of suffering

80h of discomfort

+

Movement restriction

100% hens undergoing

1min of agony

45h of pain

5h of suffering

30h of discomfort

+

Skin lesions

48% hens undergoing

1min of agony

5h of pain

4min of suffering

30h of discomfort

+

the same for the other 127 afflictions

=

During its lifetime, a caged hen undergoes on average:

6 minutes of agony

385 hours of pain

448 hours of suffering

448 hours of suffering

3.THE MAIN RESULTS

We can therefore quantify the suffering of a hen in different breeding systems.

By applying the same method to other animals involved in egg production (chicks, parents, etc.), we can calculate the overall suffering footprint for the production of an egg.

During its lifetime, a caged hen undergoes on average:

6 minutes of agony

385 hours of pain

448 hours of suffering

3000 hours of discomfort

During its lifetime, a barn-raised hen experiences on average:

6 minutes of agony

385 hours of pain

448 hours of suffering

3000 hours of discomfort

The production of an egg by a caged hen caused:

6 minutes of agony

385 hours of pain

448 hours of suffering

3000 hours of discomfort

The production of an egg by a barn-raised hen caused:

6 minutes of agony

385 hours of pain

448 hours of suffering

3000 hours of discomfort

It is time to ban caged hens in France for good

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