Periparturient hypocalcaemia (milk fever) is a disorder of Ca metabolism in
dairy cattle primarily affecting multiparous cows. The major reasons for the
rapid decrease of blood Ca concentration after calving 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. In man, vitamin D
receptor (VDR) gene polymorphisms are reported to be associated with
disturbances of Ca metabolism, whereas data confirming the same in dairy cows
are still missing. Moreover, polymorphisms that only affect non-coding regions
are sometimes difficult to ascribe to a specific disorder as pathways and
unequivocal links remain elusive. Therefore, the idea of the present study was
to investigate in a small group of dairy cows with documented clinical records
whether polymorphisms in the coding regions of the VDR gene existed and
whether these potentially found variations were correlated with the incidence
of periparturient hypocalcaemia. For this purpose, blood DNA was isolated from
26 dairy cows in their 4th to 6th lactation, out of which 17 had experienced
hypocalcaemia at least once, whereas 9 cows had never undergone periparturient
hypocalcaemia in their lifetime. The 10 VDR exons and small parts of adjacent
introns were sequenced and compared with the Bos taurus VDR sequence published
on NCBI based on the DNA of one Hereford cow. In total, 8 sequence alterations
were detected in the fragments, which were primarily heterozygous. However,
only 4 of them were really located on exons thereby potentially causing
changes of the encoded amino acid of the VDR protein, but were not correlated
with the incidence of periparturient hypocalcaemia. Certainly, this lack of
statistical correlation could be due to the small number of animals included;
anyhow, it was not encouraging enough to initiate a larger study with hundreds
of cows and document blood Ca levels post partum for at least four lactations