Milk protein variants are highly associated with milk performance traits in East Friesian Dairy and Lacaune sheep

In total, 403 milk samples of East Friesian Dairy (EFD) and Lacaune (LAC) sheep hold in three different flocks in Switzerland and Germany were analysed for milk protein variability at protein level by isoelectric focusing and at DNA-level by different DNA-based tests. Isoelectric focusing of all milk samples led to the identification of the alphas1-casein (αs1-CN; CSN1S1) alleles C and H, αs2-CN (CSN1S2) A, B, and C, as well as beta-lactoglobulin (β-LG; LGB) A and B. All animals were monomorphic for alpha-lactalbumin (α-LA; LALBA) A and kappa-casein (κ-CN; CSN3), and within beta-casein (β-CN; CSN2) only differences in the intensity and not in the position of the bands could be identified.DNA-based tests differentiated αs1-CN C into CSN1S1*C′ and C″, typed for CSN1S2*G, for an A > G single nucleotide polymorphism (SNP) in exon 7 of CSN2, for an A > G SNP in exon 2 of ovine CSN3, and for a microsatellite within intron 3 of CSN3. CSN1S2*G and the A > G-SNP within CSN2 occurred only in LAC, whereas the A > G SNP in CSN3 was identified only in EFD sheep. In total, 11 CSN3 microsatellite alleles were observed. Furthermore, 8 and 11 CN haplotypes (CSN1S1-CSN2-CSN1S2-CSN3) were identified in EFD and LAC sheep.Additionally, associations between milk performance traits and milk protein alleles and genotypes were analysed using 150-day-lactation data. Significant effects of milk protein alleles and genotypes on protein content were identified. In both dairy sheep breeds CSN1S1*C″ is significantly associated with a higher protein content. In EFD significant effects of the CSN3-SNP and the CSN3 microsatellite on protein percentage and of the LGB-SNP on protein and fat percentage were additionally identified. Further research is needed to clarify in more detail the effects of milk protein variability on milk performance also in other dairy sheep breeds, to aim the implementation in future sheep breeding programs.