Altering poultry sex ratios

Chickens, like most animals, typically produce equal numbers of males and females. But this natural sex ratio doesn't always work in the poultry industry's economic favor. A University of Georgia researcher is working on ways to skew the chicken's sex ratio to help the industry streamline production and make more money.

Chickens are big business in Georgia, worth $4.9 bln in 2008, or 41% of the state's total agricultural value. For the broiler sector of the poultry industry, the females are less profitable. On average, male broilers weigh half a pound more than females at market age, and they eat 5% less feed. However, in the egg-laying sector, the females are prized over males, obviously, because males can't grow up to produce eggs.

Kristen Navara, a poultry scientist with the UGA College of Agricultural and Environmental Sciences, is trying to determine how to control avian sex ratios.

"In nature, it is a necessary strategy to adjust offspring sex in relation to the environment," she said. "Humans, rodents, birds all skew sex ratios. It is clear females need the ability to adjust offspring for the environment where they will be born or hatched into."

Navara has recently studied skewed sex ratios in hamsters and humans in relation to day length. She is now looking for the mechanism that can control the ratios in poultry and finches. She's using hormones, particularly corticosterone, to find that mechanism.

Injecting female birds with a burst of corticosterone just before ovulation produced a sex ratio skewed toward males, or 81%. She believes she can flip the ratio to favour males or females using hormones or aggravates, which stop the secretion of corticosterone.

Sara Beth Pinson, a graduate student in Navara's lab, is coordinating studies to determine the optimal dose of corticosterone to produce the desired result. They are also testing different durations of the hormone treatment to determine how long-term treatments affect offspring sex. Research results could be available in 6 months.

This research "is something the industry has been looking for for years," said Mike Lacy, head of the CAES poultry science department. "The US poultry and egg industry funded Dr. Navara to do this research because it is something the industry is very interested in."

It is important to note that no chickens used for food are given hormones. Navara's research is only using hormones to discover the mechanism. "Broilers are not treated with hormones. "So far, the hormone injections seem to work, but what we want to do is find the mechanism the hormone is working through and then produce a non-hormonal treatment for the birds. That is the optimal way to go," she said.