Effects of Genotype Environment Interaction on Productive Traits of Holsteins Friesian in Libya

Abstract

Breeding values (BV) for some productive and reproductive traits of Holstein Friesian under Libyan conditions were estimated and compared with those estimated under, European, and North American conditions in an attempt to assess the genotype environment interaction. To investigate the effect of managerial conditions on the same traits, the heritability coefficients were also estimated under Libyan and Dutch managements. The trait's variance and covariance components and the breeding values of sires were computed using the REML method based on mixed model containing the fixed effects of month of calving, year of calving, management and generation and the random effect of sires. The lactation period and age at calving were used as covariates. Genetic correlation values of EBV for the milk yield traits were less than 1. Differences in heritability estimates due to the management system and or to environmental factors reflect Genotype x Environment interaction. Milk yield traits except dry period had a higher EBV during the Libyan than Dutch management. Reproductive traits except Age at first calving also had a higher EBV during Dutch than Libyan management. Correlations between EBV for milk yield ranged between 0.16 and 0.56 during Libyan, European and North American conditions. EBV of both North American and European sires were medium, low and negatively ranked under Libyan environment. EBV of milk yield traits showed higher variability under the Libyan environment. Sires with low EBV (> 500) revealed negative ranking under the Libyan conditions.