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Rapid growth in broiler chickens

Fast Growth in Broiler Chickens: Suffering on a grand scale

Every year, 72 billion broilers are raised worldwide. Of these, more than 90% are fast-growing "conventional" breeds, which suffer terribly as a result of the unnatural speed of their physical development.

Pollo de engorde

Broiler unable to stand due to physical deformities. Photo: Equalia

Mia Fernyhough, farm food animal welfare specialist

February 25 2022

Fast growth in chickens reared for meat (“broilers”) is a key welfare concern, with recent research evidencing it as the major contributor to many of the welfare issues we see in fast growing broiler breeds(1). There are 72 billion broiler chickens produced across the globe each year (2). Seventy-two billion. Of these, over 90%, are ‘conventional’ fast growing strains that suffer terribly as a result of their unnaturally rapid physical development. Growing to their full body weight in as little as 35 days, their prematurely grown, malformed bodies prevent them performing normal behaviours and lead to higher rates of disease and mortality. Research has shown that switching from fast growing to slower growing breeds is the single most effective  thing we can do to improve welfare outcomes for these birds (1).

Unnaturally big, unnaturally fast

We’re all too familiar with the images of chickens in crowded and filthy sheds, and the obvious suffering this causes. But it is the genetics - the unnaturally fast growth - of these birds that causes the most harm. The majority of chickens eaten globally are from one of 3 genetics companies, all virtually identical in their growth patterns. Reaching their full slaughter weight in as little as 35 days, their growth rate has quadrupled in the last 50 years. At the same time, the amount of breast meat on an individual bird has increased by two-thirds (3). This exceptionally fast growth, concentrated on the development of breast muscle, puts a huge strain on their immature bodies, leading to skeletal, cardiovascular and behavioural problems – their bodies simply cannot cope.

Pollo de engorde

Broiler unable to stand due to physical deformities. Photo: Equalia

Broilers and laying hens

Fast growing breeds are up to three and a half times as likely to suffer painful lameness and up to twice as likely to be found dead or require culling compared to slower growing commercial breeds (4). They are inactive (1,5), spending most of their day sitting, and this inactivity generates a vicious cycle; sitting on dirty, excrement laden litter means they’re more likely to have painful lesions of the footpads and hocks (ankle joints) (1,2,5). The presence of these lesions make it more painful for them to walk so they sit more, getting up only to eat and drink.

But broilers have the same desire and motivation to perform a range of natural behaviours as their laying hen cousins.

Broilers are motivated to perch, to dust-bathe, to play (1). But their bodies prevent them from doing so.

Imagine being trapped by your own body; too painful and too big to perform normal, simple, but important, behaviours. This is the reality for fast-growing broilers; they spend less time walking, running, foraging, preening, dustbathing (5), exploring and playing (1), and more time sitting and eating/drinking than higher welfare birds.

More natural, slow-growing chicken breeds

Slower growing broiler breeds exist and the scientific evidence of their welfare benefits is impossible to ignore.  These birds take 2 to 3 weeks longer to reach their final slaughter weight and as a result have better health and a richer behavioural repertoire. Utilising these higher-welfare breeds - together with providing more space and an enriched environment - would greatly improve the welfare for the billions of chickens farmed for meat production every year. The numbers of chickens farmed for meat is so high that if just 10% of UK chicken production switched to higher welfare, the lives of 100 million chickens would be improved each year!

The Better Chicken Commitment (also known as the European Chicken Commitment)

Seeing the scale and severity of the suffering of chickens on factory farms, a coalition of animal protection organisations, including The Humane League UK, joined together to find a solution. We agreed upon a set of criteria that would become the leading standard for chicken welfare across the food industry, these include:

  • The use of slower growing and higher-welfare breeds.

  • Lower density of chickens on farms.

  • Environmental enrichment (including natural light and perches).

  • Improved methods of slaughter.

  • Effective auditing.

We named it the Better Chicken Commitment (European Chicken Commitment) and this has successfully driven the industry forwards toward higher welfare practices from producers, retail, hospitality and restaurants.

Empresas alimentarias con presencia en España que han asumido el Compromiso Europeo del Pollo

Food companies with a presence in Spain that have assumed the European Chicken Commitment. Image: Equalia

The first time I saw slower growing broilers I was surprised to see them sparring, dustbathing and even running, but I shouldn’t have been surprised - they’re chickens afterall, and this is their natural behaviour! But I was, because I was so used to seeing their unnaturally overgrown counterparts. Chickens behaving like chickens shouldn’t be a surprise to anyone, it should be the norm. With the overwhelming evidence in favour of higher-welfare slower growing genetics, it’s time for food companies to commit to ensuring that these sensitive and complex animals are given a life worth living, instead of enduring a life of suffering on factory farms.


Mia is a farm animal welfare specialist who has worked for high profile NGOs to influence industry policy and standards for over 13 years. She has specialised in poultry welfare since 2014 and currently works for The Humane League UK, providing technical support to its Open Wing Alliance members.


1 Rayner, A.C., Newberry, R.C., Vas, J. et al. (2020) Slow-growing broilers are healthier and express more behavioural indicators of positive welfare. Sci Rep 10: 15151

2 Baxter M, Richmond A, Lavery U, O’Connell NE (2021) A comparison of fast growing broiler chickens with a slower-growing breed type reared on Higher Welfare commercial farms. PLOS ONE 16(11): e0259333.

3 Zuidhof, M. J., Schneider, B. L., Carney, V. L., Korver, D. R. & Robinson, F. E. Growth, efficiency, and yield of commercial broilers from 1957, 1978, and 2005. Poultry Science 93, 2970–2982 (2014)

4 RSPCA (2020) Eat, Sit, Suffer, Repeat: The life of a typical meat chicken.

5 Dixon LM (2020) Slow and steady wins the race: The behaviour and welfare of commercial faster growing broiler breeds compared to a commercial slower growing breed. PLOS ONE 15(4): e0231006

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