Frequency of bovine Nramp1 (Slc11a1) alleles in Holstein and Zebu breeds

Natural resistance against brucellosis in cattle is linked to the Nramp1 gene, which encodes a divalent cation transporter that localizes in the phagolysosome membrane in macrophages. Nramp1 gene in mouse plays a critical role in innate immunity favoring bacterial killing by macrophages in addition to its influence on adaptative immunity. Polymorphisms at the bovine Nramp1 3' untranslated region (3'UTR), detectable by Single Strand Conformational Analysis (SSCA), are associated with natural resistance against brucellosis. Such polymorphisms are associated with variation in the number of GT repeats. This study compared the frequency of Nramp1 3'UTR polymorphisms between Zebu and European bovine breeds. Eighty-one Holsteins (Bos taurus taurus) and 167 Zebu (Bos taurus indicus), including the following breeds: Nelore (n = 95), Guzera (n = 37), and Gir (n = 35), totaling 248 pure breed cattle studied. DNA extraction was performed using the guanidium protocol and genotyping was performed by SSCA. DNA from cattle considered genotypically resistant to brucellosis resulted in a single band (homozygous) with 175 bp, corresponding to the 3'UTR with 13 GT pairs (GT13), whereas DNA from genotypically susceptible cattle generated one single band with 177 bp (homozygous GT14) or double bands with both 175 and 177 bp, or 175 and 179 bp (heterozygous GT13/GT14 or GT13/GT15, respectively). A marked difference in the frequency of alleles was detected between the Zebu and Holstein cattle. Holsteins had an extremely homogeneous genotype, with 100% of the individuals with a GT13 genotype. In sharp contrast the Nelore breed had the most heterogeneous genotype with four allelic combinations, namely, homozygous GT13, homozygous GT14, heterozygous GT13/GT14, and heterozygous GT13/GT15. When the Zebu breeds were compared to each other, the only significant difference observed was the frequencies of the genotypes GT13 and GT14 between the Nelore and Guzera breeds. The knowledge of allelic frequencies in different breeds of cattle may prove to be very useful in the future for planning breeding strategies for selection of resistant cattle.