Changes in egg quality traits during the last phase of production: is there potential for an extended laying cycle?

1. A field study was conducted to investigate the deterioration of eggshell quality at end of lay, and examine the potential to extend the production cycle. A total of 1,200 eggs were assessed originating from commercial farms in Belgium: eggs were at random sampled at the collection belt at 57-65 wk of age and at the end of the production cycle (74 to 92 wk). 2. Based on a linear mixed model, egg quality was estimated for an average flock at 60 wk and changes in quality traits were predicted until the end of the laying cycle. 3. Egg weight increased (P ≤ 0.001) by 0.07 g every week from 60 wk of age onwards and shape index decreased by 0.04 unit weekly (P<0.001). Haugh unit decreased weekly by 0.38 unit (P<0.001), relative yolk weight was unaffected after 60 wk of age. Relative albumen weight showed a weekly increase of 0.02 % (P = 0.004) and relative shell decreased by 0.02 % weekly (P ≤ 0.001) until end of lay. 4. Shell quality traits were also influenced by age: shell index decreased by 0.013 g weekly (P ≤ 0.001), shell thickness (P ≤ 0.001) was calculated to be 0.23 µm thinner every week, deformation increased by 0.06 µm weekly (P ≤ 0.001) from 60 wk to the end of the laying cycle. Variability of the deformation of eggs indicated more heterogeneous shell quality at the end of the production cycle. Dynamic stiffness increased (P = 0.03) from 60 wk of age on. 5. Laying hens were depopulated on average at 80 wk of age (varying from 74 to 92 wk). Although ageing had a significant effect on most of the egg quality traits, egg quality was still acceptable at end of lay, indicating the potential to extend the laying cycle.