The relationships between the genetic polymorphisms of the 6 main milk proteins have been extensively investigated in the bovine species, although some conflicting results have been reported. The aim of this study was to compare the milk protein structure and their effect on milk traits in three breeds, Italian Friesian (IF), Italian Brown (IB), and Italian Red Pied (IRP). More than 450 proven sires were selected within each breed. The four milk caseins (aS1-CN, ?-CN, aS2-CN, and k-CN) and the two whey proteins, a-lactalbumin (a-LA) and ?-lactoglobulin (?- LG), were genotyped at the DNA level within the corresponded genes (CSN1S1, CSN2, CSN1S2, CSN3, LGB, LALBA) by SNP genotyping. A total of 13 SNP were considered allowing the identification of the main genetic protein variants or groups of variants as well as some polymorphisms within the non-coding sequences. Associations between each SNP and the estimated breeding values (EBV) for milk, protein and fat yield and protein percent were evaluated within each breed. Favourable effect of the k-CN B variant were observed in all breeds, mainly related to protein yield (IB, IRP) and protein percent (IF, IRP). Two casein variants were specifically typed in the IF; ?-CN I was significantly associated with protein yield (+22.57 kg) and protein percent (-0.04%), whereas k-CN E negatively affected milk yield (-257.8 kg) and fat yield (-13.2 kg). The aS1-CN C variant was favourably associated to protein percent (+0.04%) in the IB, where a higher effect was found (+0.07%) for a SNP within the CSN1S1 promoter. Significant effects were found in all breeds for LGB, both for the SNP associated to the main ?-LG protein variants (A and B), and for a SNP within the LGB promoter. The trends of the effects were different in the 3 breeds for the yield traits, whereas LGB A variant was positively associated with protein percent (+0.02%) in IB and IF. Association with the traits were also calculated after reconstruction of the haplotypes considering all the 13 SNP. Results demonstrate the importance of considering milk protein polymorphisms and the classic protein variants in breeding programmes.
Effects of milk protein polymorphisms on milk traits: an across-breed study
S Chessa;
2013
Abstract
The relationships between the genetic polymorphisms of the 6 main milk proteins have been extensively investigated in the bovine species, although some conflicting results have been reported. The aim of this study was to compare the milk protein structure and their effect on milk traits in three breeds, Italian Friesian (IF), Italian Brown (IB), and Italian Red Pied (IRP). More than 450 proven sires were selected within each breed. The four milk caseins (aS1-CN, ?-CN, aS2-CN, and k-CN) and the two whey proteins, a-lactalbumin (a-LA) and ?-lactoglobulin (?- LG), were genotyped at the DNA level within the corresponded genes (CSN1S1, CSN2, CSN1S2, CSN3, LGB, LALBA) by SNP genotyping. A total of 13 SNP were considered allowing the identification of the main genetic protein variants or groups of variants as well as some polymorphisms within the non-coding sequences. Associations between each SNP and the estimated breeding values (EBV) for milk, protein and fat yield and protein percent were evaluated within each breed. Favourable effect of the k-CN B variant were observed in all breeds, mainly related to protein yield (IB, IRP) and protein percent (IF, IRP). Two casein variants were specifically typed in the IF; ?-CN I was significantly associated with protein yield (+22.57 kg) and protein percent (-0.04%), whereas k-CN E negatively affected milk yield (-257.8 kg) and fat yield (-13.2 kg). The aS1-CN C variant was favourably associated to protein percent (+0.04%) in the IB, where a higher effect was found (+0.07%) for a SNP within the CSN1S1 promoter. Significant effects were found in all breeds for LGB, both for the SNP associated to the main ?-LG protein variants (A and B), and for a SNP within the LGB promoter. The trends of the effects were different in the 3 breeds for the yield traits, whereas LGB A variant was positively associated with protein percent (+0.02%) in IB and IF. Association with the traits were also calculated after reconstruction of the haplotypes considering all the 13 SNP. Results demonstrate the importance of considering milk protein polymorphisms and the classic protein variants in breeding programmes.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
