High variability of milk protein genes in Bos indicus cattle breeds of Cameroon and Nigeria and characterization of a new α_s1-casein promoter allele

Abstract

The study provides the first comprehensive information on the variability of milk protein genes of Bos indicus and Bos taurus cattle breeds in Cameroon and Nigeria. The investigations indicate a high diversity of milk protein genes for the zebu populations. Of the investigated alleles, 21 out of 29 were observed. The method of single strand conformation polymorphism (SSCP) was a particularly useful technique because it allowed discrimination of alleles, including zebu-specific alleles at the CSN2 (I) and CSN3 (A_I and H) loci, not separated by protein electrophoretic techniques and also made possible the detection of a further CSN1S1 5′ promoter allele (CSN1S1Prom⁵), which is also zebu-specific. Characterization of CSN1S1Prom⁵ showed that it was the most variable of all described CSN1S1 promoter alleles. A potential GATA consensus motif is created by mutations in CSN1S1Prom⁵. Intra-breed diversity measured as mean effective number of alleles was higher in the zebu populations than in the taurine breeds. Of the expected casein haplotypes, 96 out of 320 were present in the studied breeds. 2-C-A-A²-H (CSN1S1Prom²-CSN1S1^C-CSN1S2^A-CSN2^A2-CSN3^H) and 5-C-A-A²-H were zebu-specific while 1-B-A-A²-B was specific to the taurines. Overall distribution of alleles and haplotypes clearly separated the zebu populations from the taurine breeds. Zebu influence on the taurine breed Namchi was detected through the occurrence of zebu alleles and haplotypes. High variability of milk proteins also means availability of resources for breed development, phylogenetic studies, and conservation and management decisions.