Early pregnancy diagnosis in cows is vital for profitable dairy
husbandry as it helps to improve reproductive efficiency and shorten
calving intervals. Any method of pregnancy diagnosis such as
rectal palpation, ultrasonography, and measurement of reproductive
hormones or pregnancy associated substances has advantages
and disadvantages in terms of testing time and accuracy of diagnosis
(Purohit, 2010; Lucy et al., 2011). Immunochemical methods
based on progesterone determination in milk or serum offer the
earliest methods of pregnancy diagnosis in cattle based on the differentiation
of pregnant and non-pregnant cows 19–21 days post
insemination (Laing and Heap, 1971). At this time point (end of
the oestrus cycle) progesterone concentrations in the milk of
non-pregnant cows should be low whereas in the pregnant cow
it will be high (>7 ng/mL).