Are chickens given growth hormones? And why broilers grow so fast

Every time a shopper stands in front of an unusually large chicken breast, the same question comes back: how many hormones were pumped into this bird to get it that size? Notice how the question is phrased — it starts with how many and why, not with whether. Poultry extension specialists at the University of Tennessee made exactly this observation in their bulletin on the subject: people do not ask whether the industry uses growth hormones, they ask why it does — the answer is assumed before the question is asked. This lesson puts the question back in order.

The short answer is that growth hormones are not used in producing meat chickens — not because anyone made an ethical pledge, but for three stacked reasons, the first of which is enough on its own: chemistry that makes them useless in feed, operational arithmetic that makes injecting them impossible in practice, and a regulation that bars their entry and use in the first place. As for the size that prompted the question, it has a different explanation, less dramatic and far more convincing: some seventy years of genetic selection, documented in experiments designed specifically to separate the effect of the strain from the effect of the feed.

Why a hormone in feed does nothing in the first place#

Hormones come in two chemical families: steroids and proteins. Steroid hormones stay active when taken by mouth — the contraceptive pill is the best-known example, a steroid hormone that passes through the digestive tract and still does its job. Protein hormones, by contrast, are broken down in the stomach, and whatever survives is extensively metabolised after leaving the gut, so they lose their effect on the body when swallowed. To have any effect they must be injected, not eaten.

And growth hormone is a protein. The most familiar comparison is insulin: there is still no oral insulin pill, because the digestive tract treats it like any other protein and breaks it down before it reaches the blood — which is why people with diabetes inject rather than swallow. Exactly the same applies to growth hormone if it were put in feed or drinking water: it would be digested and rendered useless. The idea of hormone-laced feed is not merely prohibited; it does not make sense to begin with.

And if it were injected, do the arithmetic#

Suppose, for the sake of argument, that someone wanted to get around that by injecting. One injection would not do it, nor would one a day: the bird would need injecting several times a day throughout the growing period for the hormone to have any real effect. Now put that requirement inside a real poultry house.

• A single commercial house typically holds between 20,000 and 40,000 birds, and one farm has several houses — hundreds of thousands of birds on a single site.
• Every one of those birds would have to be caught by hand and injected, then caught again several times the same day, then again daily for weeks on end.
• For scale: the United States alone had roughly 32,000 broiler farms in 2022, according to USDA figures.
• And repeatedly catching a bird is not a neutral act: it is stress that raises mortality and harms welfare, so the cost is not only labour hours.

In other words, the operation is logistically impossible before it is legally prohibited. The Tennessee specialists add the point that completes the picture: modern strains are already selected to grow to their physiological limit without hormones, and pushing them faster does not yield more meat — it yields health and welfare problems and higher mortality. The hormone here is not a forbidden advantage producers quietly wish for; it is a tool they neither need nor benefit from.

So why did the chicken get bigger? An experiment built to answer that#

In 2003, researchers at North Carolina State University published in Poultry Science an experiment simple in idea and decisive in result. They took two strains: the 1957 Athens-Canadian Randombred, preserved without selection, and the commercial 2001 Ross 308. Then they raised each on two different diets: one representing 1957 formulations and one representing 2001. Four groups, and only two variables: the bird and the feed. That is the only design that answers the question conclusively, because any comparison between yesterday's chicken and today's in the market mixes the two factors together.

These were the average body weights at 42 days of age:

• 1957 bird on 1957 feed: 539 g.
• 1957 bird on 2001 feed: 578 g.
• 2001 bird on 1957 feed: 2,126 g.
• 2001 bird on 2001 feed: 2,672 g.

Read those numbers twice. Modern feed, with all its precision on energy and protein, added about 39 g to the 1957 bird — roughly seven per cent. Conversely, when the 2001 bird was fed 1950s rations it lost about a fifth of its weight, and still came out nearly four times heavier than the 1957 bird eating exactly the same food. The variable that moves the weight is the bird, not the bag.

The researchers offer an even clearer comparison. The 2001 bird on its own feed reached 1,815 g at 32 days of age with a feed conversion of 1.47, whereas the 1957 bird on its own feed would not have reached that weight until 101 days, at a feed conversion of 4.42. Reaching the same weight now takes about a third of the time and about a third of the feed. Not one hormone entered this experiment.

From 1957 to 2005: half a century in numbers#

In 2014, researchers at the University of Alberta repeated the idea from another angle in the same journal. This time three strains: two preserved without selection since 1957 and since 1978, plus a 2005 Ross 308, all raised together on the same modern nutritional programme to 56 days of age. The feed is held completely constant, so any difference that shows up is down to what accumulated in the strain alone. The results:

• Broiler growth increased by over 400% between 1957 and 2005.
• Feed conversion ratio halved over the same period.
• Live weight at 42 days rose at a compound annual rate of 3.30%, while feed conversion at the same age fell by 2.55% a year across 48 years.
• Pectoralis major yield rose 79% in males and 85% in females, while abdominal fat fell — selection did not only add size, it changed how meat is distributed on the carcass.

The scientific value of these two experiments is not only in the numbers but in the existence of a genuine control: university flocks that kept the 1957 and 1978 strains alive, unselected, through all the decades since. That control is what turns the comparison from an impression — chicken used to be different — into a controlled experiment any researcher can repeat. Without it, the whole debate would be duelling memories.

Three fields made the difference, and none of them is a syringe#

If it was not a hormone, what happened? Specialists attribute the improvement to parallel progress across several fields, three of which take most of the credit:

• Genetics: the generation interval in chickens is short — broiler breeders produce offspring in roughly six to eight months, so breeders evaluate fifteen to twenty generations in a decade, against only three to five in cattle, which need two to three years just to reach reproductive maturity. That speed is what let poultry geneticists cut roughly one day per year off the time to a target weight.
• Nutrition: every strain and every target market weight has its own feed formulation, tuned for energy, protein, vitamins and minerals, and different again for meat birds, hatching-egg birds and table-egg layers. There is no single chicken feed.
• Management and environment: temperature, ventilation, air quality, lighting, and feeder and drinker space appropriate to each age. Moving production indoors took the weather almost out of the equation — and without that environment neither the genetic nor the nutritional potential shows up at all.

Together these three are the whole explanation, and none of them works alone. Anyone looking for a single dramatic cause — a shot, a secret powder — is looking for a much simpler story than what actually happened.

And the situation in Saudi Arabia#

At the regulatory level, the supervising authorities in the Kingdom — represented by the Ministry of Environment, Water and Agriculture — prohibit the use of hormones in livestock projects, and do not permit their clearance, entry or use either on their own or within feed inputs. The ban does not stop at injecting the bird; it covers the door through which the substance could enter the country and the feed.

On the verification side, the Riyadh Region agriculture directorate announced — in a statement carried by the Saudi Press Agency in November 2016 — the results of a campaign run jointly with four other ministries across poultry projects, shops and markets: 4,780 random samples of locally produced chicken were collected and sent to the ministry's toxicology laboratory, and all came back free of hormones, growth promoters and antibiotic residues. The statement is regional and dated, so it should not be read as every year's result in every region — but it does show how verification actually works: random samples pulled from the market itself, a reference laboratory, and a published result.

It matters not to conflate this file with the antibiotics file — conflating them is what keeps the argument going in circles. Hormones are prohibited outright, so there is no withdrawal period and no maximum residue limit for them; the ban is absolute. Antibiotics are a legitimate medical use for treating sick birds, controlled through withdrawal periods, maximum residue limits and a laboratory that verifies both. Two different questions, two different answers.

Hormone-free on the pack: what it actually means#

Since the use is banned for everyone, hormone-free on a chicken pack does not describe a feature of the product; it describes the regulation that applies to every product like it. The claim is true, but it does not distinguish one brand from another — much like gluten-free on a bottle of water: accurate, and useless for choosing. Its only real problem is that it can imply the opposite: that some other pack on the shelf is not.

If you want to read a pack usefully, the information that genuinely separates one product from another is the production and expiry dates, the storage temperature required and whether the shelf you took it from was holding it, the slaughterhouse and its certification, and net weight against price. Claims that every product shares by law add nothing to your decision — and do not deserve a price premium.

The numbers in context: hormones are in all food#

One last point helps put the whole worry at its true scale. Hormones are not a foreign substance added from outside; they are chemical messages secreted by organs in every living creature, humans included. Any food of animal origin therefore contains a natural amount of them, and many plant foods contain compounds that mimic their effect. These examples come from a table in the University of Tennessee bulletin, measured in nanograms per 500 grams of food:

• Defatted soy flour: about 755 million nanograms.
• Tofu: about 300,000 nanograms. Peanuts: about 100,000.
• Eggs: about 555 nanograms. Butter: 310. Milk: 32.
• Beef from an implanted steer: 7 nanograms, against 5 from a non-implanted one.

Before comparing these figures directly, note a methodological caveat the bulletin itself states: the animal-product numbers are measured as estrone and estradiol, the plant-product numbers as isoflavones, and the two are neither the same thing nor equal in potency — the comparison is about orders of magnitude, not equivalence. Even so, the most important context is that the human body itself produces more each day than any of the above: around 513,000 nanograms of estrogen daily in a non-pregnant woman, and around 136,000 in an adult man.

The practical takeaway#

1. Growth hormones are not given in chicken feed because they are proteins digested in the stomach and lose their effect — not because anyone chose to forgo something useful.
2. If they were injected, every bird would need several injections a day in houses holding tens of thousands, which is operationally impossible before it is legally banned.
3. The size of the modern bird is the result of documented genetic selection: over 400% more growth between 1957 and 2005, with feed conversion halved.
4. The decisive experiment fed a 1957 bird 2001 rations and gained only seven per cent, while a 2001 bird on 1957 rations stayed four times heavier.
5. In the Kingdom, hormone use in livestock is prohibited by regulation, including within feed inputs, and verification runs through samples pulled from the market and tested in a laboratory.
6. Hormone-free on a pack describes the regulation, not the product — do not pay a premium for it.