The world's largest chicken breeder has discovered that a key breed of rooster has a genetic issue that is reducing its fertility, adding to problems constraining US poultry production and raising prices at a time when beef prices are already at record highs.

The breed, Aviagen Group's standard Ross male, is sire through its offspring to as much as 25 per cent of the nation's chickens raised for slaughter, said Aviagen spokeswoman Marla Robinson.

Sanderson Farms, the third-largest US poultry producer and one of Aviagen's largest customers, said it and Aviagen systematically ruled out other possible causes for a decline in fertility before determining a genetic issue was at the root of the problem.

The issue is hitting an industry that is already suffering from a short supply of breeder birds.

The US Agriculture Department last month reduced its US chicken production forecast for 2014, predicting only a 1 percent increase in poundage from 2013, well below the long-run annual average of 4 per cent. The agency predicted 2015 production would be up only 2.6 per cent.

The limited growth in output is occurring as foreign demand for US chicken is on the rise. US exports of poultry for meat are projected to reach 3.4 million tons in 2014, up from 3.1 million last year.

Aviagen, owned privately by EW Group of Germany, provides breeding stock - hens and roosters - to Sanderson and other chicken producers, which then breed the birds and hatch their eggs to produce meat.

Sanderson last summer first identified an unusual reduction in chick output involving the Ross breed. Mike Cockrell, Sanderson's chief financial officer, said about 17 percent of eggs laid by Aviagen hens mated with the rooster breed failed to hatch. Typically, the failure rate is about 15 percent, he said.

Sanderson gradually eliminated a number of other potential factors, including the temperature in hatcheries and the source of corn fed to the birds, Cockrell said.

Aviagen sent a team of scientists to Sanderson last autumn to study the issue and has acknowledged that an undisclosed change it made to the breed's genetics made the birds "very sensitive" to being overfed, he said.

"We fed him too much. He got fat. When he got big, he did not breed as much as he was intended to," Cockrell said about the breed of rooster. "The fertilization went way down, and our hatch has been way down."

Aviagen regularly tweaks genetics in birds to improve them, Cockrell added.

Aviagen declined comment on changes to the rooster's genetics.

The chicken breeding company has replaced the breed suffering from fertility issues with a new breed, and is mating it with the same type of hens. It is too early to provide accurate projections for their productivity, but "results to date are favorable," Robinson said.

Sanderson expects to fully shift to the replacement breed by autumn, Cockrell said.

The fertility problem is occurring at a time when the industry is dealing with a shortage of breeder birds, which are in demand as the sudden hike in beef prices this year has renewed demand for chicken.

The shortfall came about after breeders reduced their flocks when a spike in feed prices in 2011 squeezed their profit margins, according to Sanderson and poultry experts. While grain prices have now fallen and demand for chicken is on the rise, US poultry breeders are still rebuilding their flocks.

Aviagen's Robinson declined to comment on the reasons breeder birds are in tight supply. The nation's other major breeding company, Cobb Vantress, owned by Tyson Foods, declined to comment for this article.

A lack of accommodation for newly born breeder birds after the 2011 cutback is slowing the rebuilding process, said Paul Aho, a consultant to Aviagen and a poultry economist.

Constrained production has helped push chicken prices in Georgia, a key market, to record highs, analysts said. Boneless skinless breasts there recently were priced at $2.21 a pound, up 4.5 per cent from a year earlier.

The production shortfall is adding 50 cents per pound to the cost of chicken breasts, which sell for about $2.02 per pound in the northeastern United States, Aho said.

The high prices would normally spur chicken companies to increase production more than 5 percent from the prior year, had more breeder birds been available, said Bill Roenigk, a former senior vice president for the National Chicken Council.

In some cases, companies are trying to hatch eggs that would have been discarded in the past for being the wrong size or damaged, he said.

"Right now they're scrambling to really put any egg in the incubator that can be in the incubator, and they're paying a price in terms of not as good hatchability," he said.

Chicken producers also are keeping their hens laying eggs longer than usual to compensate for the lack of new birds - as many as five weeks beyond their typical cut-off age of 65 weeks. Eggs from older hens tend to hatch at a lower rate.

JP Morgan in March said the number of eggs per laying hen fell below the 10-year average for the first time since 2010.

"They don't have enough of these breeder birds and they also don't have the quality that they would have had 10 years ago," said Will Sawyer, vice president of food and agribusiness research for Rabobank.

There is no sign that the tight supply of breeder birds and drop in hatchability threatens human health.

High chicken prices due to the production constraints have helped push up the stock prices of Tyson and Sanderson this year, by about 17 percent and 38 percent, respectively. Both Tyson and Sanderson reported net income more than doubled in their fiscal second quarters.

The price increase is especially painful for consumers as prices for steaks chops are up 10 percent this year due to drought and disease affecting herds.

"There's nothing cheap to buy," said Ron Prestage, president-elect of the National Pork Producers Council.

Shawna McLean, who lives with her husband and dog in Playa Del Rey, California, said she now chooses meats based on what is on sale. "I'm looking at the same chicken and the price has gone up about $3 in the last month," said the 48-year old, who is looking for a job.-Reuters