Genetic structure and composite genotype distribution at Oxytocin (OXT) - Oxytocin Receptor (OXTR) loci in Italian Mediterranean river buffalo.

In the last years, several association studies between milk production traits and markers located in candidate genes have been carried out in buffalo species. In particular, an association between a G→T transversion at the 170th nucleotide of the second exon, responsible for the Arg97→Leu amino acid substitution, at the Oxytocin (OXT) locus and milk yield in buffalo has been already found. In this work we carried out a polymorphism detection at Oxytocin Receptor (OXTR) locus and an analysis of the genetic structure and composite genotype distribution at OXT and OXTR loci in Mediterranean river buffalo. The OXTR sequence analysis evidenced a C→T transition at 129th nucleotide of the third exon responsible for the Arg353→Cys amino acid substitution. Genotyping for above mentioned two SNPs was performed in the KBiosciences laboratory (http://www.kbioscience.co.uk). The investigation at the OXT locus was carried out on 562 buffaloes reared in different farms located in Campania (Southern Italy). The genotype distribution was 294 G/G, 214 G/T and 54 T/T, with a frequency of 0.713 for the G allele. This result is in agreement with that one already reported for 170 buffaloes belonging to an experimental herd located in the same region. The genotyping of the same subjects at the OXTR locus showed a distribution of 332 C/C, 194 C/T and 36 T/T, with a frequency of 0.763 for the C allele. The investigated population is in HW equilibrium. The observed OXT-OXTR composite genotype frequencies were: 0.3060:CC-GG, 0.2278:CT-GG, 0.1815:CC-TG, 0.1335:CT-TG, 0.0569:TT-GG, 0.0356:CC-TT, 0.0302:TT-TG, 0.0196:CT-TT and 0.089:TT-TT. The results obtained from this work represent the first example of genetic polymorphism detected at OXTR locus in ruminants, thus opening the way to further interesting studies. It is possible, for instance, to hypothesize that in buffalo the Oxytocin Receptor different amino acid composition by such alleles could be responsible for a different Oxytocin-Oxytocin Receptor system function and regulation. So, the detected polymorphism at OXTR locus such as the OXT-OXTR composite genotypes could represent useful genetic markers to estimate their effects on milk production traits in buffalo, but further association studies with milk recording data are needed to evaluate their potential use.