Postpartum uterine involution is necessary for the normal reproduction of dairy cows. The study aimed to investigate the pattern of postpartum uterine involution and the impact of parity on uterine involution in Chinese Holstein dairy cows. The diameter of the uterine cervix, pregnant uterine horn, and non-pregnant uterine horn were monitored using a B-mode veterinary ultrasound scanner at 5, 10, 15, 20, 25, 30, 35, and 40 days, respectively, after parturition in both multiparous and primiparous dairy cows. Meanwhile, the concentrations of hydroxyproline, E2, and IGF-1 were detected using ELISA at 5, 10, 15, 20, 30, and 40 d after parturition in both multiparous and primiparous dairy cows. Furthermore, the duration of uterine involution was compared in the multiparous and primiparous dairy cows. The results demonstrated that the diameter of the uterine cervix and the pregnant uterine horn did not decrease any further at 25 days postpartum for both the multiparous cows and the primiparous cows. Hydroxyproline levels gradually decreased with uterine involution; however, there was no significant variation in IGF-1 concentrations during uterine involution in the dairy cows. Although E2 concentrations of the peripheral plasma displayed an upward trend from day 5 to day 15 in the two groups of postpartum cows, there was no significant difference between the two groups during uterine involution. These results suggest that postpartum uterine involution was around 25 days postpartum in both the primiparous dairy cows and the multiparous Chinese Holstein dairy cows. Parity did not affect uterine involution in the postpartum Chinese Holstein dairy cows. The hydroxyproline levels of the peripheral blood may be an indicator of uterine involution in postpartum cows. Nonetheless, IGF-1 and E2 levels of the periphery blood are not associated with uterine involution in Chinese Holstein dairy cows.
Keywords: E2; IGF-1; dairy cows; hydroxyproline; uterine involution.