1 / 14

Breeding for disease resistance : Some examples

Breeding for disease resistance : Some examples. The context Cost of disease Definition of disease resistance Measurement of resistance to a pathogen Genetic variability of disease resistance Prospect for genetic improvement of disease resistance Conclusion. The context.

gabby
Download Presentation

Breeding for disease resistance : Some examples

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Breeding for disease resistance :Some examples The context Cost of disease Definition of disease resistance Measurement of resistance to a pathogen Genetic variability of disease resistance Prospect for genetic improvement of disease resistance Conclusion

  2. The context The new European agricultural policy :Increase in production is no longer a priority Some current drugs used in animal production could be banned Research focus on ecological management and animal welfare Resistance to diseases and product quality are becoming important goals in Europe

  3. Economic consequences of disease include : Loss of rabbit meat sales (mortality, lower growth rate) Increased culling rate Cost for veterinary treatment Increased work in animal management (culling, treatment) Cost of disease

  4. Definition of disease resistance Infection Different mechanisms of the pathogen and of the host Depending on the stage of infection the resistance appears as : all or none : mortality/survival, morbidity/absence of symptoms … Quantitative : number of bacteria in target organ, fever …

  5. Definition of disease resistance Resistance/sensitivity depending on pathogenic stage during an infectious process (Lantier and Vu Tien Khang, 1988)

  6. Definition of disease resistance Resilience : ability to continue a normal production life for an animal which has been infected by a parasite Potential source of infection for flock mates ? Specificity of resistance NRAMP1 gene (sheep) : control infection of Salmonella, Leishmania and various Mycobacteria Sheep with alleles ARQ are susceptible to natural scrapie but resistant to some different scrapie strains (BSE)

  7. Measurement of resistance to a pathogen Direct measurement Survival analyse : describes the length of healthy life The survivor function gives the proportion of animal still healthy at time t (from 4 to 10) The statistical model includes explanatory variables : year-season effect, size of the originating litter, parity, genetic effect Ex : Crusader growing rabbits : Signs of illness are recorded from week 5 to week 10

  8. Measurement of resistance to a pathogen Direct measurement Total number of pasteurellosis signs over the growing period All or none trait : healthy/sick

  9. Genetic variability of disease resistance Polygenic approach Infinitesimal model Dominant model in selection Genetic parameters : Heritability : The relative importance of heredity in determining phenotypic values Genetic correlation : Genetic links between traits The genetic value of an individual = Sum of independent and small effects of a very large number of genes

  10. Genetic variability of disease resistance Polygenic approach : Crusader rabbit survey Heritability of resistance to pasteurelosis : 0.08 (number of weaned : 0.06 ; ADG 5-10 weeks :0.30) Correlation with Weight Gain Correlation with Litter size at weaning (estimates of litter size effect in survival analyse) Trait Healthy animals Sick animals Weight at 10 weeks (kg) 1.94 1.80 Weight gain 5–10 w (kg) 1.10 0.96

  11. Genetic variability of disease resistance Major genes Some genes have a major effect on susceptibility to disease A large number of major genes have been found in the human The number of such genes is limited in livestock : . the Weaver disease in Cattle . the scrapie in sheep (PrP gene) . the malignant hyperthermia in pigs (halothane sensibility gene)

  12. Prospect for genetic improvement of disease resistance Interest of breeding for disease resistance Economic interest in rabbit Salmonella in sheep (abortus ovis) : efficient vaccines are available Scrapie in sheep : no vaccination and no treatment Selection is very appealing in this case Reducing mortality of weaners from 15% to 10% gives an extra $ 16 per doe per year Increasing growth rate by 3 g/hd/day gives an extra $ 11 per doe per year Depend on the efficiency of the non genetic approach (environment, vaccination, treatment, culling of infected animal)

  13. Prospect for genetic improvement of disease resistance The cost of breeding for disease resistance Direct costs : Challenge in controlled conditions Laboratory analyses (antibodies level, faecal eggs count) Genotyping (PrP gene) Indirect costs : Negative effects on production traits (unfavourable correlations ; ex : mastitis in dairy cattle) Loss in selection pressure on other traits

  14. Conclusion Susceptibility to disease is influenced by genetic factors Estimation of heritability are medium, similar to the values of production traits A number of questions are still remaining Correct definition of resistance measurement Cost of resistance measurement Consequences of selection on theses trait (resistance to other disease, resistant animals remains diffusers of pathogens)

More Related