The use of selective breeding to produce more robust and resilient animals, is no longer just a pie in the sky idea.

Modern technology in combination with a greater understanding of the genetic make up of animals, is allowing this idea to become a greater reality.

Genetic markers associated with specific poultry diseases as well as improved resistance has already been identified. The challenge now is to breed new lines containing these attributes.

Theo Bezuidenhout, Cobb South Africa manager, explained that breeders are targeting some of the traits that are more difficult to select for, such as avian immunity, disease tolerance and disease resistance.

Identifying and investigating DNA markers in the chicken genome can enhance progress. Cobb Vantress has made large investments and is collaborating with world class research institution to continuously better understand the genome. The challenge however is to select for birds with greater immunity to disease without affecting their performance, according to him.

Commercialising birds with these traits also won’t happen overnight.

Mr Bezuidenhout explained that it took time to breed these genetic enhancements and testing resilience is both costly and risky. He foresees that progress will be faster with the development of new screening and testing technologies that would help to evaluated selection efficiency.

Increased resilience

The general trend when it comes to the selection for disease resistance, has been towards the breeding of birds with stronger immune systems and not against specific diseases, according to Dr Christina Swaggerty, research microbiologist at the United States Department of Agriculture.

She pointed out that the host immune response to pathogens in the earliest stages of infection is a critical determinant of disease resistance and susceptibility: “The relatively recent discovery that the innate immune response directs the acquired response, supports efforts to select poultry with an efficient early innate immune response.”

She explained that microbial recognition by cells of the innate response activates intracellular signalling pathways that result in the activation of microbicidal killing mechanisms, release of cytokines and chemokines, and production of co-stimulatory molecules required for antigen presentation to the acquired immune system.

While such birds have not yet become commercially available, there are laboratories and breeders that have achieved this goal.

The United States Department of Agriculture along with Cobb-Vantress, for example, developed a breeding strategy through which sires were selected upon key immune markers, namely the cytokine (IL6) plus chemokines (CXCLi2 and CCLi2).

Trials to evaluate the strategy, proved that multi-generational selection based on this breeding strategy produced birds that were naturally more resistant to Salmonella Enteridis, Eimeria tenella, Clostridium perfringens-induced necrotic enteritis and Campylobacter jejuni (although data on Campylobacter jejuni has not yet been published).

Dr Swaggerty said the results of their selection study is very important, as Salmonella and Clostridium are two of the leading causes of bacterial-derived foodborne illnesses worldwide: “By increasing resistance of the birds against these diseases, the risks of humans contracting these diseases via poultry products could be significantly reduced.

"In addition to being a foodborne pathogen, Clostridium perfringens is also one of the causes of necrotic enteritis, with necrotic enteritis, together with Eimeria (coccidiosis) currently being two of the most costly pathogens facing the poultry industry.”

The trials also looked at the impact of selection on broiler performance traits. According to Dr Swaggerty, the selection for increased resistance did not have a negative impact on the feed conversion ratio or percentage breast meat yield at six weeks of age, but live weight was slightly lower than in the control group.

To keep up with global consumption, consumer demand and increasing regulations, Dr Swaggerty foresees that alternative breeding strategies resulting in a more robust bird with enhanced natural resistance will become increasingly important and in higher demand across the world.

“Traditional selection strategies based on growth and feed conversion ratio have been the primary means of selection over the past sixty years.

"Breeder companies typically have to anticipate industry needs at least five years ahead and it takes about ten years to develop new lines.

"A selection strategy based on a phenotype characterised by enhanced pro-inflammatory cytokines or chemokines could accelerate the process of breeding poultry with improved robustness, liveability and resistance against a broad range of foodborne disease and poultry pathogens,” she said.