Oestrone Sulphate can be used as a very sensitive pregnancy test in horses and demonstrates the presence of a live foal, if the foal dies the O-SO4 decreases very rapidly. O-SO4 starts to rise from about 80 days post covering, increases steadily to above 25 ng/mL and remains detectable until very close to term.

O-SO4 may also be used in cows and donkeys as a late pregnancy test and in goats to distinguish between true pregnancy and “cloudburst”. Pigs have an early O-SO4 peak about 25-35 days and again at 80-110 days.