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Common diabetes drug can help aging hens lay more eggs for longer

What do chickens and people with a common reproductive disorder have in common? More than one might think—and a widely-used diabetes medication might just be the surprising link.

At Penn State, researchers discovered that metformin, a drug usually prescribed for type 2 diabetes and polycystic ovary syndrome (PCOS) in humans, can actually help chickens lay more eggs. Specifically, it helps broiler breeder hens—the chickens that produce the broiler chickens we eventually eat—stay fertile and produce eggs for longer, even as they age.

While the team has known that metformin can help egg production in chickens for a couple of years, they recently discovered how it works. They their findings in the Biology of Reproduction.

Broiler breeder hens have been selectively bred for decades for their offspring to grow quickly and reach market weight fast—a trait that helps meet the world's demand for affordable chicken meat. But there's a trade-off: As these birds age, their ability to lay eggs declines rapidly, limiting how long they can remain productive. This drop in fertile egg production resembles PCOS in humans, which also affects fertility and ovarian function. That's where metformin, a common treatment for PCOS, enters the picture.

PCOS, a hormonal disorder affecting women characterized by irregular menstrual cycles, is the most widespread endocrinological condition, affecting roughly 4% to 12% of women, and the main cause of infertility in women, according to the National Institutes of Health. Metformin is often used off-label to treat PCOS symptoms, improving insulin sensitivity, lowering excess hormone levels and helping to regulate menstrual cycles, potentially aiding fertility.

In a 2023 study in Reproduction, researchers at Penn State gave a group of hens a small daily dose of metformin over 40 weeks. The results were striking: The hens laid more fertile eggs, had lower body fat and showed healthier reproductive hormone levels than those not given the drug.

"These findings suggest that metformin can significantly improve ovarian function in broiler breeder hens," said Ramesh Ramachandran, senior author on the study, professor of reproductive biology in the College of Agricultural Sciences.

The researchers then dug deeper to find out what exactly was happening inside the birds' bodies—and they found the answer in the liver. The liver plays a key role in bird reproduction, as it's where egg yolk precursors are made. Using advanced gene sequencing techniques at Penn State's Huck Institutes of the Life Sciences, the team analyzed RNA—genetic material that regulates many biological functions—from liver samples.

Their findings, published in their latest paper in Biology of Reproduction, revealed that metformin "switched on" several genes involved in producing yolk proteins and maintaining stable blood sugar. At the same time, it "switched off" genes linked to fat buildup—mirroring how metformin works in humans with metabolic disorders.

"Essentially, metformin helps older hens stay metabolically healthier, which lets them keep producing eggs well beyond their usual decline," said Evelyn Weaver, a postdoctoral researcher and lead author on both studies.

This finding could have major implications for poultry farming, the researchers said. By extending egg production in broiler breeder hens, farmers may be able to reduce flock turnover, improve animal welfare and increase efficiency—all while using a medication that's affordable and safe. Metformin is quickly metabolized by these hens, Weaver pointed out, so it poses no risk of entering the human food supply.