Poultry: Vets optimistic that yolk sac infections will continue to decrease

Monday, August 9, 2010

Quality control, temperature testing, culling of weak chicks and use of antibiotics are among the measures that can give chicks a better chance of survival

by PATRICIA GROTENHUIS

While cases of yolk sac infections went up in 2009 – an increase attributed to the wet year we had, which aids in bacteria growth – Dr. Lloyd Weber, a poultry veterinarian and poultry farmer from Guelph, says this year the infections seem to have decreased by 50 per cent.

"I believe there have been advancements. There are quality control factors, like breeders can't sell floor eggs or dirty eggs," says Weber.

Yolk sac infections are caused when the egg encounters a bacterial load, which is then passed on to the newly hatched chick. They account for losses of approximately half of one per cent of chicks, and with ongoing improvements to egg and chick care, the incidence is expected to continue decreasing.

Yolk sac infections target all species of commercial birds. According to Dr. Bruce Hunter, professor of avian pathology at the Ontario Veterinary College in Guelph, the last day before chicks hatch, the body wall closes at the navel. Sometimes, body wall closure is incomplete at hatching, providing an entry point for bacteria.

Yolk sac infections occur in two ways, says Hunter. One is egg contamination prior to hatching through poor collection and storage techniques, allowing bacteria to enter through the shell. These chicks may die prior to hatching or be weakened by a yolk sac infection that becomes septicemic. As well, if the hatcher is contaminated, bacteria may enter chicks through the navel, leading to infection of the navel and yolk sac.

Dr. Rachel Ouckama, general manager of Curtis Chicks of Port Hope and also a poultry veterinarian, says hatcheries' quality assurance programs are crucial to limiting the incidence of yolk sac infections.

Curtis Chicks has a breeder service department to visit breeders regularly to ensure standards are met. Temperatures of egg rooms are tested, farmers are shown proper handling of eggs, chickens are taught to use nesting boxes, and records are kept documenting the environment and egg quality of each farm.

Ouckama says the infections are cyclical in nature, occurring most often in summer and winter. To limit infections, breeder farmers must use extra ventilation in the summer and supplemental heat in cool weather, along with more frequent egg collection to keep eggs in the controlled environment of the egg room longer.

The first five days of a chick's life are critical in fighting infections. Weber says that culling weak chicks and decreasing stress can improve overall flock health, while Ouckama suggests the use of antibiotics can give chicks the extra help they need.

Although dirty eggs can be a big culprit in yolk sac infections, Ouckama stresses there are more factors at work.

"There isn't a direct relationship between dirty eggs and yolk sac infections. It depends on how well the egg and bird fights infection," says Ouckama.

Eggs can fight bacterial infections, and no egg or chick is sterile. As long as infections are kept at reasonably low levels, average birds should be able to fight them off, says Ouckama. E. coli, salmonella and pseudomonas are all causes of yolk sac infections, Weber says.  Pseudomonas can cause eggs to explode in the setters at the hatchery, which in turn contaminates hundreds of other eggs. In this way, eggs can be infected in setters and hatchers, even though all quality control protocols are followed.

Weber says there is a history of eggs infected with salmonella coming from the United States due to lower quality control measures there, but he is optimistic the trend is decreasing.

Currently, 20 per cent of hatchery eggs are imported. 

"The risk will go down in the future. Conditions will continue to improve," says Weber. BF