RELATIONSHIP BETWEEN LAYING AGE AND REPEATABILITY OF EGG QUALITY TRAITS

Résumé

Repeatability of 22 -, 26, 30 - and 32 - week egg weight (EW)., shell thickness (ST), Haugh (1955) unit (HU), yolk index (Yl)and shape, index (SI) was estimated based on the first three eggs laid in the week by fifty - six commercial Harco pullets. There was a consistent increase in repeatability estimates for these traits as laying age progressed. The estimates ranged from 0.67 to 0.85, 0.53 to 0.84., 0.51 to 0.87, 0.20 to  0.61 and 0.26 to 0.52 for EW, ST, HU, YI and Si, respectively. While repeatability of EW  increased by 0.02 units per week, that of HU increased by 0.03 and 0.04 unit per week, respectively. Repeatability of EW, ST and HU showed a linear relationship with age, whereas that of YI and ȘI showed a linear relationship with age, whereas that of YI and SI showed a curvilinear relationship with age. The general increase in repeatability of each trait with age indicates that fewer records will be required to adequately characterize the inherent producing ability of each hen for the trait as laying age progressed.