No evidence that selection for egg production persistency causes loss of bone quality in laying hens

Ian C Dunn,Robert H Fleming,Dirk-Jan De Koning,Alejandro B Rodriguez-Navarro,Estefania Sanchez-Rodriguez,Björn Andersson,Cristina Benavides,Matthias Schmutz,Heather A Mccormack,Nazaret Dominguez-Gasca,Peter W Wilson

doi:10.1186/s12711-021-00603-8

Abstract

BackgroundThe physiological adaptations that have evolved for egg laying make hens susceptible to bone fractures and keel bone damage. In modern laying hen breeds, longer periods of egg laying could result in a greater risk of poor bone quality, and selection for increased egg production has frequently been stated to be a cause. However, the existing literature does not support this hypothesis. To test the hypothesis that egg production is associated with quality, breaking strength and density of bone, genetic correlations between these traits were estimated in White Leghorn and Rhode Island Red breeds. Genetic correlations of cortical and medullary bone material chemical properties with bone quality were also estimated, in order to identify methods to improve bone quality with appropriately targeted measurement of key traits.ResultsEstimates of heritability for bone quality traits were moderate (0.19–0.59) for both White Leghorn and Rhode Island Red breeds, except for the keel bone trait, which had a heritability estimate equal to zero. There was no evidence for genetic or phenotypic relationships between post-peak egg production and bone quality. In the White Leghorn breed, the estimate of the genetic correlation between pre-peak production/age at first egg and bone quality was significant and negative (− 0.7 to − 0.4). Estimates of heritability of thermogravimetric measurements of tibial medullary bone mineralisation were significant (0.18–0.41), as were estimates of their genetic correlations with tibia breaking strength and density (0.6–0.9).ConclusionsThe low genetic correlation of post-peak egg production with bone quality suggests that selection for increased persistency of egg production may not adversely affect bone quality. Onset of puberty and mineralisation of the medullary bone, which is a specialised adaptation for egg laying, were identified as important factors associated with the quality of the skeleton later during egg production. These are traits for which genetic, as well as environmental and management factors can positively impact the overall quality of the skeleton of laying hens.

Highlights

The physiological adaptations that have evolved for egg laying make hens susceptible to bone frac‐ tures and keel bone damage
The Rhode Island Red (RIR) hens were heavier than the WLa and White Leghorn b (WLb) hens (Table 1), which may explain in part their higher tibia breaking strength due to increased loading
The heritability estimates for tibia breaking strength and total egg production were 0.69 ± 0.08 and 0.23 ± 0.07, respectively, and there was no significant genetic correlation between these two traits (0.02 ± 0.16)

Summary

Introduction

The physiological adaptations that have evolved for egg laying make hens susceptible to bone frac‐ tures and keel bone damage. There is a fear that the increasingly persistent laying hen, which has great benefits for sustainability but leads to a longer period of production, may be associated with greater risk of poor bone quality in end-of-lay hens [5]. In this context, it is frequently stated, including by ourselves, that poor bone quality is caused by intense selection for increased egg production [5,6,7,8]. While the physiology of laying eggs, as opposed to not laying eggs, can be related to potential issues of poor bone quality, it is not clear that the phenotypic relationship between number of eggs laid and bone quality is negative [9]

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Discussion

Conclusion