author(s)
Al-Janabi HRA, Al-Rawi AJ and Al-Anbari NN

abstract
This study was conducted on 50 Holstein cows at Al Salam Station for dairy cows, over the period from 1/11/2016 to 1/11/2017. Determination of the genotypes at the position LEP/Sau3AI of Leptin gene and the relationship with some of productive traits in Holstein cows. Genotype differed for the target leptin gene encoding region due to different genetic bundles resulting from enzymatic digestion, which were genotyped in both AA and AB and their distribution ratios were 80.00 and 20.00 % respectively, and that the differences between these percentages were highly significant (P<0.01 ), and allele frequency were 0.90 and 0.10 for both A and B respectively. The results of the present study showed that the total milk production and the lactation period for the Holstein cows were significantly affected (P<0.01) by the Genotype of the leptin gene and for the cows with heterozygous Genotype AB. There was a significant variation (P<0.01) in the period from birth to the peak of production, at 44.95 ± 0.85 and 33.78 ± 1.73 days for the two genotypes AA and AB respectively, as for the length of the production of peak reached the two genotypes in the same order 46.78 ± 0.94 and 60.46 ± 1.92 days (P<0.01). The percentage of fat was significantly affected (P<0.05) by genotypes of the Leptin gene, reaching the highest percentage of cow milk with the Genotype of AA (3.93 ± 0.62%) and the lowest of the genotype AB (3.69 ± 0.30%), while the percentage of lactose, protein and non-fat solids and specific gravity of milk had not significantly affected by the genotypes of leptin gene. It could be concluded by studying the genotypes of leptin gene that could be adopted in the development of genetic improvement strategies in milk cows to maximize the economic return of their breeding projects by selecting and crossing the genotypes that achieved the best economic characteristics.