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Allelic variations in the bovine vitamin D receptor gene in dairy cows: correlations with periparturient hypocalcemia? Carolin Deiner, Maria Reiche, Anne Moesch, , Holger Martens
Periparturient hypocalcemia (milk fever) is a disorder of Ca metabolism in dairy cattle that occurs around parturition and primarily affects multiparous cows1. The major reasons of the rapid decrease of blood Ca concentration are the prompt increase of Ca secretion into the colostrum and the delayed activation of Ca regulation mechanisms including calcitriol, a metabolite of vitamin D . Vitamin D receptor (VDR) gene polymorphisms are reported to be associated with variations of Ca metabolism in man. The present study investigated the potential existence of VDR gene polymorphisms in German Holstein Friesian cows and correlated resulting variations with the incidence of hypocalcemia. Blood DNA was isolated from 26 high-yielding cows in their 4th to 6th lactation, out of which 17 had experienced hypocalcemia with ionized serum calcium levels < 0.9 mmol/l at least once, whereas nine cows had never undergone periparturient hypocalcemia in their lifetime. The ten VDR exons and parts of adjacent introns were sequenced and compared with the Bos taurus VDR sequence published on NCBI based on breed Hereford. In total, eight sequence alterations were detected in the fragments, which were primarily heterozygous (only on one allele). Four of them were located on exons and caused potential changes of the encoded amino acids. Calculated p-values (Fishers exact probability test) were all > 0.05, hence, sequence variations found were not correlated with the incidence of periparturient hypocalcemia in this study.