Relationship between Bone Stability and Egg Production in Genetically Divergent Chicken Layer Lines

Abstract

Impaired animal welfare due to skeletal disorders is likely one of the greatest issues currently facing the egg production industry. Reduced bone stability in laying hens is frequently attributed to long-term selection for increased egg production. The present study sought to analyse the relationship between bone stability traits and egg production. The study comprised four purebred layer lines, differing in their phylogenetic origin and performance level, providing extended insight into the phenotypic variability in bone characteristics in laying hens. Data collection included basic production parameters, bone morphometry, bone mineral density (BMD) and bone breaking strength (BBS) of the tibiotarsus and humerus. Using a multifactorial model and regression analyses, BMD proved to be of outstanding importance for bone stability. Only for the tibiotarsus were morphometric parameters and the bone weight associated with BBS. Within the chicken lines, no effect of total eggshell production on BBS or BMD could be detected, suggesting that a high egg yield itself is not necessarily a risk for poor bone health. Considering the complexity of osteoporosis, the estimated genetic parameters confirmed the importance of genetics in addressing the challenge of improving bone strength in layers.

Keywords: animal welfare; bone breaking strength; bone mineral density; fractures; laying hens; laying performance; osteoporosis; phylogeny.

Figure 1

Schematic illustration of the experimental setup (A) and related data collection (B). In two consecutive generations, four chicken layer lines were allocated to a diet containing either 300 or 3000 IU of vitamin D3. During the experimental period, data on egg number, egg quality, feed consumption and body weight were collected as indicated. Post mortem, bone morphometry, bone mineral density and bone breaking strength were assessed.

Figure 2

Heatmap of Pearson’s correlation coefficients between bone traits (BBS, bone breaking strength; BMD, bone mineral density; W, bone weight; L, bone length; T, bone thickness) of the tibiotarsus (Tib) and humerus (Hum) in laying hens of the genetic lines WLA (A), R11 (B), BLA (C) and L68 (D). Red indicates a positive correlation; white represents no correlation and blue represents a negative correlation. Significant correlation coefficients are marked with asterisks (* p < 0.05; ** p < 0.01; *** p < 0.001).

Figure 3

Standardised regression coefficients (β) ± standard errors of regression of bone mineral density, bone weight, bone length and bone thickness pertaining univariately to the bone breaking strengths of the tibiotarsus (A) and humerus (B) in four different chicken layer lines (WLA, R11, BLA, L68). Significant regression coefficients are marked with asterisks (* p < 0.05; ** p < 0.01; *** p < 0.001).

Figure 4

Regression coefficients (β) ± standard errors of regression of total eggshell production pertaining to the bone mineral densities of the tibiotarsus (A) and humerus (B), and the effect of total eggshell production on the bone mineral densities of the tibiotarsus (C) and humerus (D) in four different chicken layer lines (WLA, R11, BLA, L68). Significant regression coefficients are marked with asterisks (*** p < 0.001).