On farm calls in county Derry today, a client revealed that of 97 cows in calf using sexed semen, 17 were carrying male calves on the basis of smart scan technology. In contrast, 80 maiden heifers were scanned pregnant and in calf to sexed semen and only 2 were carrying male calves.
You might ask the question why a higher percentage of the dairy cows were in calf to male calves with sexed semen.
In my opinion, this anomaly is associated with the fact that high production type cows will have a uterine environment that is not conducive to the survival of early stage embryos compared with those in maiden heifers. In Saudi Arabia, the sex ratio of calves born favours a disproportionately high percentage of males born in the stressors placed on these cows in a harsh environment with high milk production creates an environment where male embryos survive better than female embryos.
Other studies show that male embryos are larger than female embryos for the same stage of embryonic development at day 13 to 14 after fertilisation. This may explain better maternal recognition for males than less developed females, giving rise to a disproportionate incidence of male pregnancies in high production type cows.