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.
In the present study, the productive and reproductive performance of German Holstein Friesian dairy cows and subsequent generations born in Libya were evaluated. The number of cows that had the first lactation record included in the study was 2094. Data were analyzed using REML to estimate factors affecting milk yield and reproductive traits. The model included: month, year of calving, management, generation, origin of sire as fixed effects and sire as random effect. In addition, age at first calving and lactation period included for milk yield traits as a covariate. Total milk yield was generally high (8409 Liters) and achieved with reproductive efficiency (110 days open) during Dutch management, and at the expense of the reproductive traits (161 days open) during Libyan Management. Management, calving year, calving month, age at first calving and lactation period had a significant effect on both milk yield and reproductive traits. In addition, milk yield and days open were affected by the Temperature Humidity Index (THI). A different trend of milk yield and days open was found during cold and hot seasons. However, Days open were more affected by the increased THI than high milk yield. Management plays important role to maintain high productivity with reproductive efficiency under heat stress conditions. .
This study investigated the interaction of poultry breeds x environment under Libyan conditions and compared with that under a temperate zone for a seven-week bodyweight. Data were collected from the weekly records during the rearing period for three grandparent breeds Hypeco, Avian, and Shaver, at Ghotsultan and Tawargha from 1986 to 2001. Traits studied were daily feed consumption, cumulative feed consumption, body weight, feed consumption ratio, and mortality. The model used to analyze the data for the rearing period was included: overall mean, the effects of location, breeds within the year, the flock, seasons, and the age. Breeds x seasons and breeds x locations interaction were found in weight at seven weeks of age. Avian showed consistent performance under both hot and cold seasons for seven weeks bodyweight (1308.3-1304.4g), while Hypeco and Shaver perform well under cold seasons but not in hot seasons in Libya. Hypeco and Avian perform less under Libyan conditions compared to temperate zone conditions, whereas Shaver performs a little better under Libyan conditions. In addition, Hypeco had lower mortality, which was about 2.84%, compared with Avian 3.0%, and Shaver, which was 4.38% during the rearing period. This study could conclude that the performance of grandparent breeds under Libyan conditions was affected by weather and management.
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