Orientation of cattle fetuses in utero in relation to stage of pregnancy

The orientation in utero of cattle fetuses was studied in 494 pregnant cows (478 singly pregnany; 16 twin pregnant). Fetuses were in anterior presentation if the head was oriented toward the cervix and in posterior presentation if the head was oriented toward the uterotubal junction. Data were considered for 10 day stages of gestation (Day 40 to 170) and for 15 day stages (Day 171 to 280). Before 100 days and between 101 and 200 days of pregnancy the proportion of fetuses in anterior presentation approximated 50%. After 201 days of pregnancy 82.7% of fetuses were in anterior presentation, and orientation was different (x-2 equals 16.49:1 df) from random (50:50). After 216 days all fetuses were in anterior presentation. Data from twin pregnancies were too few to be conclusive, but no trends were dissimilar from those in singly pregnant cows. Anterior presentation of fetuses is assumed not later than 216 days of gestation in normal pregnancies.