The Danger of Fat Chickens

Reading Time: 5 minutes

Joan was always a plump chicken. Part of it probably had to do with genetics; as a Dominique, she’s considered a dual-purpose breed. Though my flock all free-ranges in the yard, and I try not to give them treats too often, she was always the first to come running, jiggling her body down the hill whenever I came out with some mealworms in my hand. When people visited the chickens and wanted to try holding one, I’d steer them away from Joan — by far the heaviest girl in my flock.  

In May 2020, I walked down to the coop to let the girls out in the yard and knew something was wrong from 20 feet away. Joan lay on her side on the coop floor, legs sticking out straight in front of her. I hoped she was just asleep or taking a dust bath even as I knew she seemed too still. Just yesterday, she’d laid an egg and been as talkative as ever. Today she was dead. I didn’t know what could have happened and decided to get a necropsy to make sure there wasn’t an invisible killer going through the flock. 

As it turned out, there was, but a virus didn’t cause it. Joan had died of an affliction I’d never heard of before but is the most common cause of death in laying hens: fatty liver hemorrhagic syndrome (FLHS) or, in plain terms, being severely overweight. Hanging around the bottom of the bird feeder, eating spilled sunflower seeds and suet crumbs, killed her. 

Joan had two inches of fat on her abdominal wall. Her liver had gotten so enlarged that it was prone to rupturing. In all likelihood, she’d jumped off a perch or down from the nest box, ruptured her liver, and bled out internally, all without me knowing anything was ever wrong with what I thought was just a pleasantly plump chicken. 

Joan had died of an affliction I’d never heard of before but is the most common cause of death in laying hens: fatty liver hemorrhagic syndrome (FLHS) or, in plain terms, being severely overweight.

Deaths from FLHS are most common in spring and summer. “In springtime, they’re more likely to put weight on,” says Dr. Marli Lintner of Oregon’s Avian Medical Center. She’s been working exclusively with birds for 30 years and treats many of Portland’s pet chickens, including my own. This springtime weight gain is caused by hormonal changes that prepare hens for egg-laying after a winter break. “You know what estrogen does to all of us,” Lintner says.

But the danger doesn’t end there. In summer, fat chickens have a more challenging time cooling themselves and are prone to heatstroke. Chickens rely on their respiratory systems to cool themselves down, Lintner says, and they can’t do that when they’re filled with too much fat. So on a hot day, which for a chicken is anything above 80 degrees F, running across the yard can be enough to give them heatstroke and cause them to keel over.  

“Fat chickens aren’t cute,” Lintner says, pointing out that even when they don’t die from it, overweight can make them more prone to issues like bumblefoot. Though Joan was plump, it’s hard to tell when a chicken has put on a few too many pounds in most cases. 

Chickens tend to have a pointy keel bone, an extension of the sternum that owners often feel when they pick up their birds and put on most of their fat internally, says Lintner. “I have people feeling on the chest expecting a big fat pad, and that’s the last place it shows up. By the time you feel a fat pad there, it’s too late.” Weighing chickens also presents a challenge since they can store up to half a pound of food in their crops.  

Luckily there are a few ways you can tell if your birds are packing on the pounds. The easiest and least intrusive way is to simply pick them up regularly. “When you pick up a chicken, it should feel slightly hollow and lighter than what you’d think a large fluffy animal should feel like,” Lintner says. Of course, this is subjective, especially since some chicken breeds are particularly fluffy while others have feathers that lie tighter to their bodies. But if you pick them up enough over time, you can get an idea of a normal baseline weight for different chickens in your flock.   

If you have a chicken that seems like it might be overweight, Lintner recommends that owners look at the skin underneath the vent. Usually, a chicken’s skin is somewhat see-through, but a fat chicken will have yellowish puckery skin that seems opaquer and has a dimpled texture like skin with cellulite.  

As for how to keep your chickens from getting fat in the first place, there are a few easy things to avoid: keep them away from birdfeeders and spilled bird food which can contain high-calorie items like sunflower seeds and suet; cat and dog food left where chickens can get to them can also lead to weight gain. Unfortunately, chickens are also social eaters, which means that if one or two birds in the flock want to stand around eating at the feeder all day, other chickens are likely to follow. If you catch your chickens hanging out by the feeder too often, switching to smaller feedings once or twice a day rather than free feeding is a good option.  

Deaths from FLHS are most common in spring and summer. This springtime weight gain is caused by hormonal changes that prepare hens for egg-laying after a winter break.

Then there’s the part that’s the easiest and hardest for loving chicken owners to pull off — make sure you’re not feeding your chickens too many treats. Lintner understands the impulse, “It’s such a social thing and so much fun.” But treats should always represent less than 10% of a chicken’s daily diet, which is about a quarter-pound of food a day for a laying hen (more for larger breeds and roosters and less for small Bantams). Lintner says that popped popcorn and freeze-dried peas and corn are good lower-calorie treat options for chickens that you can’t resist spoiling. 

After I learned why Joan died, I put the rest of the flock on a diet. Now I hand out treats sparingly and created a poultry netting fence around the bottom of the bird feeder to keep the chickens out. Though I initially felt bad, the girls hardly noticed the difference anymore and still come running when they see me walking toward them, hoping that I have some treats in hand — even if they are low-calorie.

Originally published in the 2021 special issue of Backyard Poultry — A Natural and Sustainable Flock — and regularly vetted for accuracy.