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[MARCH 25, 2004]  URBANA -- Serendipity means looking for one thing and finding something else that proves to be more valuable than the original object. The concept manifested itself recently in the University of Illinois Department of Animal Sciences when a researcher came across an unexpected phenomenon that may eventually mean an added $36 million for U.S. poultry producers.

"We were working on a project involving the effects of estrogen in roosters. Lack of sufficient levels of estrogen can leave roosters sterile," explained Janice M. Bahr, a professor of reproductive physiology. "As part of the research, we were examining roosters' reproductive tracts and kept encountering stones. We began looking into what was causing the stones, and at first we thought the condition might result from too much calcium in the feed. But we found out that calcium had nothing to do with the development of these stones, which also lead to reproductive problems."

The search for the cause of the stones has unexpectedly indicated that the problem is connected to a vaccine given chickens to prevent avian infectious bronchitis virus. This very common virus affects only chickens and not other poultry animals or humans. To prevent it, chickens are immunized several times with a slightly altered version of the virus. And the vaccine works well in protecting hens and roosters from the virus.

However, Bahr's research has turned up a previously unknown side effect: the formation of stones in the reproductive tract of roosters. A colleague at the University of Arkansas first suggested looking at the vaccine after Bahr's investigation of calcium in chicken feed proved it was not the culprit.

"We took fertilized eggs we knew were pathogen-free for the experiment," Bahr said. "After the chicks were hatched, we injected the vaccine in one group of roosters, based on the industry-recommended vaccination schedule, and did nothing to the other. Eight out of 10 immunized roosters had stones. None of the roosters that were not injected with the vaccine had stones."

The fact that the vaccine can lead to stones in the reproductive tract of roosters sheds light on a fertility problem in broiler chickens. In the broiler industry, most hens are fertilized by roosters, although there is some artificial insemination. There is only a 60 percent fertility rate in floor-mating and a slightly better 65 percent fertility rate for artificial insemination.

"This is most likely a problem with the sperm. We now know that vaccinated roosters have lower fertility rates," said Bahr. "We found that vaccination with the avian infectious bronchitis virus results in a reduced testosterone level by as much as 50 percent."

Maximum hatchability is a prime concern of poultry producers, she added. Each hatched egg translates into profit. Today, the hatchability rate in the broiler industry is 83 percent.


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"If we could just raise the hatchability level by 1 percent, it would mean $36 million more per year for the broiler industry," she said.

In the past, Bahr said, the industry has not worried too much about the low fertility rate because of the "sheer number" of birds in a given poultry operation. "The solution was usually seen as simply putting more roosters on the floor," she said.

"If roosters are producing sperm that are only effective 60 percent of the time, that's a waste of resources," Bahr said. "Simply putting more roosters on the floor is not the answer."

The challenge now is to come up with a vaccine against the avian infectious bronchitis virus that prevents the disease without reducing rooster fertility.

While the vaccine has been used for many years and the fertility rates have had the same challenge for many years, researchers had not previously considered a correlation between the two. In part, Bahr said, that is because research -- like the economics -- in the poultry industry, as well as with most livestock, has an emphasis on the female of the species.

"You want to develop sows that can produce more pigs, cows more calves, ewes more lambs, and chickens more eggs or chicks," she explained. "That accounts for a reason why this connection wasn't made sooner or more research focused on the problem. Even though chicken is the world's number one source of meat, there wasn't much attention paid to the rooster."

Bahr's research was initially supported by the USDA's Animal Health and Disease Program. She has requested support from the U.S. Poultry and Egg Association and the USDA.

One paper has been published on the project, and another one will be in the near future. This novel discovery linking vaccination with suppressed fertility in the rooster will be presented at the World Poultry Congress in June in Istanbul, Turkey, and at the Society for the Study of Reproduction meeting in August in Vancouver.

"As with many exciting discoveries, finding the connection between the vaccine and the infertility of roosters was an example of serendipity," said Bahr.

[University of Illinois news release]


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