Blood samples were not collected until the day of slaughter as it has been shown, for example,
that blood sampling of cows can cause a substantial delay in the onset of oestrus from 54
to 85 h (Walton et al., 1987). Furthermore, while it would have been useful to carry out
repeated ultrasound scanning of follicles to determine the time of ovulation this was not
undertaken due to its association with severely compromised conception rates