Mortality is an economically important trait usually handled as a discrete outcome from hatch time until selection in most broiler breeder programs. However, in other species, it has been shown that not only does the genetic component change over time, but also there are maternal genetic effects to be considered when mortality is recorded early in life. This study aimed to investigate alternative trait definitions of mortality with varying models and effects. Three years' worth of data were provided by Cobb-Vantress, Inc. and included 2 mortality traits. The first trait was binary, whether the bird died or not (OM), and the second trait was a categorical weekly mortality trait. After data cleaning, 6 wk of data for the 2 given mortality traits were used to develop 5 additional trait definitions. The definitions were broiler mortality (BM), early and late mortality (EM & LM), and 2 traits with repeated records as cumulative or binary (CM and RM, respectively). Variance components were estimated using linear and threshold models to investigate whether either model had a benefit. Genomic breeding values were predicted using the BLUP90 software suite, and linear regression validation (LR) was used to compare trait definitions and models. Heritability estimates ranged from 0.01 (0.00) to 0.16 (0.01) under linear and 0.04 (0.01) to 0.21 (0.01) under threshold models, indicating genetic variability within the population across these trait definitions. The genetic correlation between EM and LM ranged from 0.48 to 0.81 across the different lines, indicating they have divergent genetic backgrounds and should be considered different traits. The LR accuracies showed that EM and LM used together in a 2-trait model have comparable accuracies to that of OM while giving a more precise picture of mortality. When including the maternal effect, the direct heritability considerably decreased for EM, indicating that the maternal effect plays an important role in early mortality. Therefore, a suitable approach would be a model with EM and LM while considering the maternal effect for EM. Single nucleotide polymorphism effects were estimated, and no individual SNP explained more than 1% of the additive genetic variance. Additionally, the SNP with the largest effect size and variance were inconsistent across trait definitions. Chicken mortality can be defined in different ways, and reviewing these definitions and models may benefit poultry breeding programs.
Keywords: accuracy; broiler survival; genetic correlations; livability.
Mortality is a significant concern in livestock species, especially in chickens, as they have been selected for fast growth and increased meat yield. Chicken mortality is currently being measured as whether the bird survives a certain grow-out period or not. However, mortality is a complex trait influenced by genetics, maternal ability, and environmental conditions throughout a chicken’s life. This study investigated alternative ways to define and model mortality to enhance current evaluation methods. Five alternative trait definitions were developed using the original phenotypes collected on the farm from 3 different chicken lines. Each trait definition was modeled and then validated using linear regression validation techniques. This study showed there are differing genetic factors influencing mortality during different points of life, including maternal genetic effects, especially in the earliest weeks of a chick’s life. Segmenting mortality into early and late and using them in a 2-trait model showed comparable accuracies while giving a more precise picture of mortality. Therefore, reviewing trait definitions and models for mortality may benefit poultry breeding programs.
© The Author(s) 2024. Published by Oxford University Press on behalf of the American Society of Animal Science.