Variation in vitelline membrane strength during the extended laying cycle in laying hens

The vitelline membrane strength (VMS) of chicken eggs is critical to liquid-egg processing, as a weakened membrane ruptures more easily during yolk and albumen separation, contaminating albumen with yolk. With the adoption of the extended laying cycle, the processing potential of eggs from older hens and stored eggs remains unclear. This study aimed to evaluate changes in VMS during the extended laying cycle and the effects of breed, storage time, and temperature, and to assess yolk-contamination risk. At each of 11 time points between 43 and 100 wk, 180 eggs per breed were collected from White Leghorn and Rhode Island Red hens and equally assigned to 0, 7, or 14 d at 25°C. An additional 180 eggs per breed were collected at 53 wk and assigned to 4, 25, or 30°C for 7 d. VMS and egg quality traits were measured using a TA-XT plus texture analyzer and an EMT-5200 egg quality analyzer, and yolk contamination proportion was calculated. Results showed that VMS across hen ages did not decline continuously throughout the laying cycle and remained above 0.86 N in White Leghorn and 0.67 N in Rhode Island Red from 72 to 100 wk. White Leghorn showed higher VMS than Rhode Island Red, with significant differences after 87 wk (P < 0.05). VMS decreased as storage time increased at 25°C. Yolk contamination showed a higher incidence of exceeding 0.2% at 14 d, a threshold relevant to baking quality. Eggs stored at 4°C had significantly higher VMS than those stored at 25°C and 30°C (P < 0.05) at 7 d. Overall, VMS was not associated with albumen height and Haugh unit (P > 0.05). Correlation analysis showed that VMS was positively associated with egg weight, yolk weight, and yolk index (P < 0.05). In conclusion, VMS did not decline continuously throughout the extended laying cycle. Given that VMS decreased with storage time at 25°C, storage at 4°C is recommended for eggs intended for liquid-egg processing.