The title of her thesis is ‘Susceptibility of broilers to colibacillosis’, with attention for the opportunities of challenge testing and indicator traits in selection strategies, of which you will find below an abstract.

With this research project Birgitte gives very valuable input for the approach of disease resistance in (broiler) breeding programmes, and within Hybro this has been and will be discussed again. This does not automatically mean that Hybro’s current approach will change a lot, but it will be at least challenged again.

Susceptibility of Broilers to Colibacillosis

Opportunities of Challenge Testing and Indicator Traits in Selection Strategies

Susceptibility of broilers to respiratory colibacillosis is an ongoing problem in the broiler industry. Genetic selection may contribute to a reduction in the problems. Birgitte Ask did her PhD on this subject at the Department of Farm Animal Health in Utrecht in collaboration with ABGC in Wageningen, Netherlands. Birgitte found that in a selection strategy context, evaluation of susceptibility of broilers to colibacillosis should be based on information on individual feed intake, daily body weights and mortality, and the presence of organ lesions. Challenge testing should be done by introducing a cocktail of pathogenic E. coli into the environment.

Alternatively to challenge testing, immunocompetence (the ability to respond immunologically to infection) is a potential indicator trait for susceptibility to disease. Selection on immunological parameters (for example, macrophage activity) has, however, not yet proven successful in this respect. Birgitte developed a model, which describes the development of the immune system in chicks. The model showed that effects of maternal immunity and development of the immune system with age in combination with challenge and measurement strategies may explain why selection for improved immunocompetence has not been successful. The model may be used as a tool in the definition of appropriate challenge and measurement strategies when it is desired to evaluate immunocompetence.