Estimate of genetic parameters of egg quality traits in Mazandaran native hens

A total of 37300 records of egg weight (EW) and 1540 records of egg quality traits, namely, albumen weight (AW), yolk weight (YW), egg shell weight (ESW), egg shell strength (ESS), egg shell thickness (EST) and haugh unit (HU) of Mazandaran native hens were used to estimate genetic and phenotypic parameters. Egg weight data collected during 1991 to 2006 and egg quality traits were measured in 3 consecutive days on 769 hens. Data were analyzed with restricted maximum likelihood procedure by using multiple-trait animal model. Estimates of heritabilities were 0.471, 0.747, 0.334, 0.595, 0.218, 0.465 and 0.536 for EW, AW, YW, ESW, ESS, EST and HU, respectively. The genetic correlation between HU and AW was positive and low (0.11), whereas it was negative and low with other egg quality traits. The EW had a positive and high genetic correlation with AW (0.95) and moderate with YW (0.45) and EST (0.39). The range of genetic correlations among all other traits varied from 0.04 (between AW and ESS) to 0.81 (between EST and ESS). These estimates for phenotypic correlations ranged from -0.13 (between YW and HU) to 0.95 (between EW and YW). These results indicated that selection based on EW may increase YW, AW and egg shell quality.