Casein proteins were repeatedly examined for protein polymorphisms and frequencies in diverse cattle breeds. The occurrence of casein variants in Holstein Friesian (HF), the leading dairy breed worldwide, are well known. The frequencies of different casein variants in HF are likely affected by selection for high milk yield. Compared to HF, only little is known about casein variants and their frequencies in German Black Pied cattle (DSN). The DSN population was a main genetic contributor to the current high yielding HF population. The goal of this study was to investigate casein (protein) variants and casein haplotypes in DSN based on the DNA sequence level and to compare these with data from HF and other breeds. In the investigated DSN population we found no variation in the alpha-casein genes CSN1S1 and CSN1S2, and detected only the αS1*B and αS2*A protein variants. For CSN2 and CSN3 genes non-synonymous SNPs leading to three different β and κ protein variants were found, respectively. For β casein protein variants A1, A2 and I were detected, with β*A1 (82.7%) showing the highest frequency. For κ casein protein variants A, B, and E were detected in DSN, with the highest frequency of κ*A (83.3%). Accordingly, the casein protein haplotype αS1*B - β*A1 - αS2*A- κ*A (order of genes on BTA6) is the most frequent haplotype in DSN cattle.

The dual-purpose German Black Pied Cattle (DSN) has become an endangered breed of approximately 2,550 registered cows in Germany. The breed is genetically related to Holstein-Friesian cattle because the old DSN breed contributed to the selection of the modern Holstein dairy cow. In dairy farms, breeders aim to improve animal health and well-being by reducing the number of mastitis cases, which would also reduce milk losses and treatment costs. On the genomic level, no markers associated with clinical mastitis have been reported in DSN. Therefore, we performed a genome-wide association study on 1,062 DSN cows using a univariate linear mixed model that included a relatedness matrix to correct for population stratification. Although the statistical power was limited by the small population size, 3 markers were significantly associated, and 2 additional markers showed a suggestive association with clinical mastitis. Those markers accounted for 1 to 3% of the variance of clinical mastitis in the examined DSN population. One marker was found in the intragenic region of NEURL1 on BTA26, and the other 4 markers in intergenic regions on BTA3, BTA6, and BTA9. Further analyses identified 23 positional candidate genes. Among them is BMPR1B, which has been previously associated with clinical mastitis in other dairy cattle breeds. The markers presented here can be used for selection for mastitis-resistant animals in the endangered DSN population, and can broadly contribute to a better understanding of mastitis determinants in dairy cattle breeds.

Recently, a Total Merit Index (RZ€) has been developed for German Holstein dairy cattle on the basis of margin in Euro. Our aim was to adjust this lifetime net merit for the dual-purpose German Black Pied cattle breed (DSN) accounting for beef production in addition to milk performance and fitness traits. We used the estimated breeding values of DSN sires and developed a breeding value for carcass weight and quality. Furthermore, we adjusted the German Holstein marginal profits per standard deviation, which are used to calculate the estimated breeding values, to DSN-specific values. The DSN Net Merit is the sum of the three sub-indices DSN Net Milk, DSN Net Fitness, and DSN Net Beef, which contribute to the DSN Net Merit with 52.84%, 43.43%, and 3.73%, respectively. The DSN Net Merit that was calculated for 33 DSN sires ranged between EUR −1114 and +709. The DSN Net Merit strongly correlates with the Total Merit Index. The implementation of the DSN Net Merit is useful for selection and mating decisions. Especially, the sub-index DSN Net Beef, which does not correlate with existing breeding values, can be used to maintain the dual-purpose character of DSN while modestly improving milk yield. The approach can be easily adapted to other dual-purpose breeds.