Heritabilities of and genetic relationships between salmonella resistance traits in broilers.

Abstract

Using experimental infections, three traits for salmonella resistance were studied: mortality, survival time (in animals that died by infection), and quantitative cecal salmonella carriage at the end of the rearing period (in animals that did not die). In total, 548 animals were used; mortality was 29.2%, mean survival time was 5.97 d (n = 160), and the mean 10log of colony forming units per gram of cecal contents was 1.62 (n = 387). Genetic parameters were evaluated in bivariate threshold-linear models to account for the selective measurement of survival time and cecal carriage. Heritabilities were .06 for survival time, .09 for cecal carriage, and .12 for mortality. The genetic correlation between mortality and cecal carriage was weak (.26), which suggests that these traits are largely controlled by different genes. The genetic correlation between mortality and survival time was relatively strong (-.68). Simultaneous study of multiple traits seems to be of particular importance in judging epidemiological consequences of a possible selection for resistance. Results here indicate that selection on decreased mortality could be unfavorable for the spread of salmonella because the resulting correlated increase in survival time, implying longer shedding by infected animals, is relatively stronger than the correlated decrease in level of cecal carriage. Selection to reduce the level of cecal salmonella carriage could be done while keeping survival time constant, if so desired, because the correlation between these traits is weak (-.15).

Use of Integrated Studies to Elucidate Potential Benefits from Genetic Resistance to Salmonella Carrier State in Fowl

“…These results are coherent with the estimations of heritability of resistance to death (0.15 and 0.12) obtained respectively by Beaumont et al, (1999) after intramuscular inoculation of dayold chicks and by Janss & Bolder (2000) after inoculation at two weeks of age. It is to notice that, according to genetic parameters estimated by the latter, more resistant animals would survive longer, contributing to a higher risk for consumers if they were still carriers.…”

Nonparametric Methods for Incorporating Genomic Information Into Genetic Evaluations: An Application to Mortality in Broilers

“…A slightly larger heritability (0.06) was reported by De Greef et al (2001) for ascites-related mortality, with even higher heritability estimates for heart-failure syndrome-related mortality (0.10), major heart-lung-related mortality (0.15), and total mortality (0.22). Janss and Bolder (2000) found a heritability estimate of 0.12 for mortality 28 days after infection with Salmonella. However, comparisons should be done cautiously, because traits were different and the estimates in the present study were based on 200 sires only (e.g., note that the 95% highest posterior density regions for heritability ranged from 0.004 to 0.05).…”

Association between in vitro heterophil function and the feathering gene in commercial broiler chickens

“…Evaluation of heterophils isolated from commercial FF lines for an innate immune response marker such as in vitro phagocytosis or bactericidal activity may be advantageous compared with further genetic selection for resistance against a single pathogen. Broilers with a reduced mortality rate to Salmonella infections shed bacteria for longer periods of time (Janss & Bolder, 2000), thereby increasing the probability of transmission to the entire flock. Selecting birds that are resistant to a single pathogen has proven to be complicated and ineffective, so it may prove beneficial for poultry breeders to select birds that have a generally efficient immune response.…”