Dynamics of occurrence of defective eggs in initial laying lines of hens

The aim of this study was to monitor the occurrence of abnormal eggs in five initial laying lines of the domestic chicken (Gallus domesticus) between 2017 and 2021. The incidence of abnormal eggs, cracks, shell-less eggs, and double-yolk eggs were examined as part of the monitoring. Also assessed was the laying intensity, which ranged from 83.7% for the Barred Plymouth Rock (BPR) B line to 96.8% for the Rhode Island Red (RIR) A line. A statistically significant relationship between the line and control year was discovered for all varieties of abnormal eggs. The highest occurrence of cracks was in the RIR B line (2.2%). The BPR A line of hens had the highest concentration of shell-less eggs (1.7%), while the RIR A line, which also had the highest laying intensity (96.8%), had the highest frequency of double-yolk eggs (1.5%). A positive trend between the intensity and the occurrence of abnormal eggs was also confirmed. The BPR B (3.4%) and BPR C (3.0%) lines, which belonged to the lines with the lowest laying intensity, had the lowest percentage of abnormal eggs. For the BPR C line, cracks (1.2%), shell-less eggs (0.9%), and double-yolk eggs (0.9%) had the lowest occurrence rates. The correlation between laying intensity and double-yolk eggs reached 0.67, and a significant positive relationship was seen. On the other hand, no association was found between the laying intensity and the prevalence of cracked or shell-less eggs. There was also a strong correlation between abnormal eggs and double-yolk eggs (0.80) and between abnormal eggs and cracks (0.73). The correlation between the total occurrence of abnormal eggs and the intensity of laying reaches a mean value of 0.41. An increase in the intensity of laying from 80% to almost 100% leads to an increase in the occurrence of abnormal eggs from 2.6% to 6.3%.