Molecular Characterization Of Selected Milk Genes In Major Cattle Populations Of Ethiopia

Abstract

Milk Genes Are Potential Candidate For Milk Production Due To Their Biological Significance On The Quantitative Traits Of Interest, Of Which Diacylglycerol O-Acyl Transferase 1 (Dgat1) And Prolactin (Prl) Genes Are Considered To Be Functional Candidates With Major Effect On Milk Yield And Composition Traits. However, It Has Not Been Well Investigated Whether The Known Dgat1 And Prl Mutations Are Segregating And Associated With Milk Yield And Milk Composition Traits In Zebu And Their Crossbred Populations In Ethiopia. Thus, This Study Was Undertaken To Assess The Genetic Variation Of Dgat1 Exon-8 And Prl Exon-4 Genes, To Estimate The Allelic And Genotypic Frequencies And To Assess The Effect Of Dgat1 K232a And Prl Variants On Daily Milk Yield And Composition Traits In Boran, Begait, Fogera, Horro And Boran * Holstein Crossbred Cattle Populations. Blood Samples For Genomic Dna Extraction And Milk Samples For Analysis Of Milk Components Were Collected From Ninety Two ((17 Boran, 16 Begait, 18 Fogera, 17 Horro, And 24 Boran * Hf Cross (75% F1 Hf*(Hf * Boran)) Randomly Sampled Cattle Populations. Gene Specific Primers Were Used To Amplify 278bp And 294bp Regions Of Dgat1 Exon-8 And Prl Exon-4 Genes, Respectively. Dna Sequencing Was Carried Out Using Sanger Method To Detect The Genetic Variation In Selected Gene Regions. Unique Accession Numbers Were Obtained For Each Haplotype Sequences Of Dgat1 (On262825 - On262849) And Prl (On677410 - On677427) Genes And Deposited In The Genebank. Heterozygosity, Polymorphic Information Content (Pic), Allele And Genotype Frequency And Test For Hardy-Weinberg Equilibrium Were Calculated Using Power Marker. Pairwise Fst Values, Neutrality Tests And Number Of Haplotypes Were Computed Using Arlequin Software. Phylogenetic Analysis Of Coding Region Was Carried Out Using Mega 11 Software And Univariate Analysis Of Variance Was Carried Out Through Glm Procedure Of Sas Software To Assess The Associations Of Detected Genetic Variation With Milk Yield And Composition. Results Revealed That Dgat1 Gene Had 11 Haplotypes; 0.615 Haplotype Diversity And 0.010 Nucleotide Diversity In The Studied Populations. Three Genotypes Aa, Ka, And Kk Were Detected In Boran * Hf Cross Whereas, Ka, And Kk Genotypes In The Boran, Begait,Horro And Fogera Populations Found To Be In Hwe. The Frequency Of K232 Was Ranged From (0.50 In Boran * Hf Cross To 0.97 In Horro) Populations. In The Boran * Hf Crosses, The Genotype Ka (0.50) Was Prevalent, Whereas In The Horro Populations Genotype Kk (0.94) Was More Prevalent. Substitution Effect Of One Copy Of K Allele Leads To Significant (P<0.01) Increase Of Fat And Protein Content And, Decrease Of Milk Yield, Lactose And Solid Not Fat Content In All Breeds Considered. Three Snps Were Identified In The Coding Region Of Prl And G.8323t>A, Showed Missense Mutation With The Presence Of Five Different Haplotypes.Substitution Effect Of One Copy Of G Allele Leads To Significant (P<0.05) Increase Of Fat, Snf And Protein Content And Decrease Of Daily Milk Yield In The Sampled Populations.Heterozygosity, Pic And Inbreeding Coefficient Revealed Genetic Variation In Dgat1 And Prl Genes. The Study Indicated That Dgat1 K232a Marker Had Significant Effects On Daily Milk Yield, Milk Fat And Lactose Content And Whereas, Snp G.8398a>G Only Have Significant Effect (P<0.05) On Average Daily Milk Yield, Fat And Solid Not Fat Percentage In All Studied Cattle Populations. Overall, The Results Of This Study Revealed That Dgat1 And Prl Genes Were Polymorphic In The Sampled Cattle Populations, And These Markers Could Be Utilized To Accelerate Future Molecular Breeding Of Dairy Cattle After Validation In Larger Populations.