|ONDRAK, JEFF - University Of Nebraska|
|WHITMAN, KATHERINE - University Of Nebraska|
|Chase, Chadwick - Chad|
|Cushman, Robert - Bob|
Submitted to: Theriogenology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/24/2017
Publication Date: 6/16/2017
Citation: McNeel, A.K., Ondrak, J.D., Amundson, O.L., Fountain, T.H., Wright, E.C., Whitman, K.J., Chitko-McKown, C.G., Jones, S., Chase, C.C., Cushman, R.A. 2017. Timing of transcriptomic and proteomic changes in the bovine placentome after parturition. Theriogenology. 100:1-7. doi: 10.1016/j.theriogenology.2017.05.020.
Interpretive Summary: Proper post-partum reproductive performance is a major contributor to reproductive efficiency in beef cows. There is minimal evidence in the literature that the onset of estrous cycles impacts rebreeding performance, but the incidence of calving difficulty is increased in repeat-breeder cows. Calving difficulty and uterine infections negatively impact rebreeding performance, both by impacting oocyte quality and uterine function. The efficacy of interventions to prevent these issues in cows experiencing calving difficulty is still minimal. Therefore, the objective of this study was to examine the mechanisms controlling normal expulsion of the fetal membranes. Using a repeated-measures model, we were able to demonstrate that separation of the membranes begins at or before expulsion of the calf and that contrary to current beliefs; it should be possible to detect aberrations in the process very early post-partum. This indicates that malfunctions in membrane expulsion may begin earlier than thought in beef cows and could contribute to decreased rebreeding performance. Future research will investigate changes in these mechanisms that are associated with calving difficulty and differences in rebreeding performance.
Technical Abstract: Proper post-partum reproductive performance is important for reproductive efficiency in beef cows, and dystocia decreases post-partum fertility. Crossbred beef cows (n = 1676) were evaluated for lifetime performance based on degree of dystocia at presentation of the first calf. Cows that experienced moderate or severe dystocia produced fewer calves during their productive life (P < 0.01). The exact mechanism is unclear, but may be due to the contributions of dystocia to abnormal placental separation. Proteolytic activity is hypothesized to contribute to placental separation in ruminants; however, when ovine placentomes were collected following caesarian section, no proteolytic activity was detected. We hypothesized that stage 2 of parturition was necessary to stimulate proteolysis and initiate placental separation. Serial placentome collections were performed on mature cows (n = 21) at hourly intervals for the first 2 h after expulsion of the calf. An intact piece of each placentome was fixed for histological evaluation, and a separate piece of caruncular and cotyledonary tissue from each placentome was frozen for transcriptomic and proteolytic analysis. A full set of placentomes was collected from only 7 of 21 cows at 0, 1, and 2 h, and all cows had expelled fetal membranes by 6 h. Histological, transcriptomic and proteolytic analysis was performed on placentomes from cows from which three placentomes were collected (n = 7). The microscopic distance between maternal and fetal tissues increased at 1 h (P = 0.01). Relative transcript abundance of matrix metalloprotease 14 (MMP14) tended to increase with time (P = 0.06). The relative transcript abundance of plasminogen activator urokinase-type (PLAU) was greater in caruncles than cotyledons (P = 0.01), and tended (P = 0.10) to increase in the caruncle between 0 and 2 h while remaining unchanged in the cotyledon over the same span of time. Greater PLAU and plasminogen activator tissue-type (PLAT) proteolytic activity was detected by zymography in the caruncle than the cotyledon immediately post-partum (P < 0.01). In the absence of calving difficulty, PLAU activity increased during stage 2, indicating that this enzyme has a primary role in placental separation in beef cows. How PLAU activity changes in cases of calving difficulty and how changes in PLAU activity may contribute to retained fetal membranes and decreased lifetime productivity remains to be examined.