Genetic variability and population structure in loci related to milk production traits in native Argentine Creole and commercial Argentine Holstein cattle

Single nucleotide polymorphisms within exon four of the prolactin gene and their effect on milk traits in cattle populations of Ethiopia

Bovine prolactin (PRL) gene is essential for the initiation and maintenance of lactation and exerts multiple effects on mammary alveoli to promote the synthesis and secretion of major components of milk. The objectives of this study were to identify mutations in PRL gene and to evaluate the mutations as potential markers of milk performance traits in cattle populations of Ethiopia. For this purpose, genomic DNA from whole blood was extracted through salting out procedure from 87 animals of five cattle populations of Ethiopia. Accordingly, three single nucleotide polymorphisms (SNPs) were identified of which one SNP g.8323T > A showed missense mutation while the other two SNPs revealed silent mutations. FST values showed statistically significant genetic differentiation among the studied populations. Intermediate polymorphic information content was noted for most SNPs, which indicates the presence of sufficient genetic variation at this locus. Two SNPs showed heterozygote deficiency as a result of positive FIS values. Only g.8398A > G SNP have statistically significant (p < 0.05) effect on average daily milk yield, fat and solid not fat percentage in all studied cattle populations. Therefore, g.8398A > G SNP identified in this study influences cattle milk production and may be used as possible candidate SNP for marker-assisted selection programs in cattle populations of Ethiopia.

Analysis of allelic pattern across milk trait genes in native cattle adapted to high altitude region of Leh-Ladakh

Ladakhi, the native cattle from Ladakh region of India have developed over the years under natural selection and can survive well at extreme climatic conditions, viz. high altitude, huge barren lands, low temperature (≤–20°C) and hypoxic conditions. Even at extreme survival conditions, this cattle provides around 2–5 kg of milk. This highly evolved germplasm might possess unique alleles or combinations of alleles, hence attempt was made to study the frequency of allelic variants at important candidate gene loci affecting dairy traits. The observed distribution pattern of allele frequencies were different from taurine but in accordance with other Indian native cattle breeds indicating maintenance of indicine characteristics and near absence of taurine influence/introgression effect on this naturally evolved germplasm. Further, variant E at κ-CN locus and two novel variants at BTN-3 loci were also observed. The present findings helped to understand the unique Ladakhi cattle population with respect to polymorphism and distribution of various alleles in candidate genes related to milk traits.

Analysis of genetic variation at the prolactin-RsaI (PRL-RsaI) locus in Indian native cattle breeds (Bos indicus)

This study assessed the distribution pattern of allelic variants at the prolactin-RsaI locus in 23 Indian native cattle breeds (Bos indicus). PCR-RFLP genotyping of a 156 bp fragment of prolactin (PRL) in exon 3 revealed the predominance of the heterozygous AB genotype (mean frequency 0.58) irrespective of utility type (dairy, dual, draft), geographic region (northern, central, southern), and coat color (red, gray) of the breeds analyzed. The overall frequencies of homozygous AA (0.22) and BB (0.20) genotypes were in a similar range. The PRL (A) and PRL (B) alleles exhibited similar gene frequencies (means 0.52 and 0.48, respectively). The existing profile of the PRL-RsaI gene locus in a large set of Indian native cattle breeds was different from that of Bos taurus and cattle breeds of other countries, where either the BB genotype and PRL (B) allele or the AA genotype and PRL (A) allele have been reported to be more prevalent.

Indigenous domestic breeds as reservoirs of genetic diversity: the Argentinean Creole cattle

Contrary to highly selected commercial breeds, indigenous domestic breeds are composed of semi-wild or feral populations subjected to reduced levels of artificial selection. As a consequence, many of these breeds have become locally adapted to a wide range of environments, showing high levels of phenotypic variability and increased fitness under natural conditions. Genetic analyses of three loci associated with milk production (alpha(S1)-casein, kappa-casein and prolactin) and the locus BoLA-DRB3 of the major histocompatibility complex indicated that the Argentinean Creole cattle (ACC), an indigenous breed from South America, maintains high levels of genetic diversity and population structure. In contrast to the commercial Holstein breed, the ACC showed considerable variation in heterozygosity (H(e)) and allelic diversity (A) across populations. As expected, bi-allelic markers showed extensive variation in He whereas the highly polymorphic BoLA-DRB3 showed substantial variation in A, with individual populations having 39-74% of the total number of alleles characterized for the breed. An analysis of molecular variance (AMOVA) of nine populations throughout the distribution range of the ACC revealed that 91.9-94.7% of the total observed variance was explained by differences within populations whereas 5.3-8.1% was the result of differences among populations. In addition, the ACC breed consistently showed higher levels of genetic differentiation among populations than Holstein. Results from this study emphasize the importance of population genetic structure within domestic breeds as an essential component of genetic diversity and suggest that indigenous breeds may be considered important reservoirs of genetic diversity for commercial domestic species.