In postpartum dairy cows, rapid uterine involution is a prere-
quisite for a high conception rate and short interval from calving
to conception (Opsomer et al., 2000). The uterus shows a distinct
size reduction during the first 3 weeks postpartum (pp), with uter-
ine contractility crucial in the process of uterine involution, partic-
ularly with regard to the removal of excessive fluid and debris and
the elimination of bacteria from the uterine lumen during the early
postpartum period (Zerobin and Sporri, 1972; Paisley et al., 1986;
Arthur et al., 1996).