You’d be forgiven for thinking “what do you mean, how do they breathe?”
Because surely, chickens breathe like any other animal, don’t they? Actually, the simple function is very different in hens. The truth is that chickens have a specialised system for getting oxygen into their body and removing carbon dioxide. They use an efficient combination of two ‘breathing’ methods to obtain oxygen meaning that their respiratory system is very different and arguably far superior to that of the human one.
More importantly, this efficient flow of oxygen allows them to indulge in their favourite highly energetic activities such as pecking for bugs and slugs and running all day long!
Humans vs. Hens – a different sort of respiratory system
Unlike humans, chickens do not have a diaphragm. In our bodies, this fibrous muscle separates the chest and abdomen and contracts regularly to draw air into our lungs. In contrast, a chicken’s lungs are attached directly to the ribcage and only expand a little when air is breathed in. The lungs don’t expand like balloons as in a human body. The ribcage in chickens is far more rigid than in mammals and provides a strong anchor point for the large flight-enabling muscles. Without a diaphragm, chickens must move their entire ribcage to draw sufficient air into their lungs.
As you might expect, air enters through your hen’s nostrils and passes through the pharynx and trachea. The trachea is protected by the larynx which makes sure food does not enter the airway when the chicken is swallowing.
The trachea branches into smaller bronchi, which enter the lungs and then branch into secondary bronchi and hundreds of small loops called Parabronchi. This results in a large surface area within a relatively small space and more efficient transfer of oxygen. In humans, air travels through the trachea and enters the lungs via bronchi that lead to alveoli. These sacs only have one opening, so air can flow in and out – known as tidal breathing, as it mimics – you guessed it – the tide!
A chicken’s trachea also branches into smaller tubes but in contrast, these the lead to secondary bronchi and hundreds of small loops called Parabronchi. In your hen’s lungs, air passes through in one direction and the gas exchange takes place in tiny blood capillaries. This results in a large surface area within a relatively small space and more efficient transfer of oxygen. Although, chickens need to inhale and exhale twice to complete a full respiratory cycle, whereas a human only has to do so once.
A bit of breathing space
Chickens have long necks because they need to preen those hard-to-reach feathers, therefore they have a longer trachea to allow a relatively large amount of air to enter in one breath.
The typical breathing rate for a hen is 12-37 breaths per minute. That’s compared to cockerels with a breathing rate of 18-20 breaths per minute and a human adult of 12–20 breaths per minute.
A hen – much like a dog – has no sweat glands, so if you notice her opening her mouth to breathe, she may be trying to regulate her temperature. However, this can also be a sign of stress, so keep a watchful eye on her – as always, the key is to familiarise yourself with your flock, so you know what is normal for your hens.
Now here’s the interesting bit… chickens also use their bones to help them breathe!
In addition to the trachea and lung system, the avian secondary bronchi lead into separate air sacs, some of which are housed in the birds’ skeletal system.
Chickens have pneumatic bones – literally, bones that ‘breathe’. Pneumatic bones contain a light honeycomb structure of air-filled cavities. As well as making the bones lighter, to allow easier flight, these bones provide a secondary route by which air exchange can occur.
The air sacs that connect to the pneumatic bones have very thin walls. They act like bellows to pull air into the comparatively rigid lungs. This allows a circular flow of air through your hen’s body.
And that’s how hens breathe!