Physiological and clinical aspects of uterine contractility during the postpartum period in cows

Abstract

The individual studies, presented in separate chapters of this thesis, were designed to get answers to certain methodological problems and biological questions associated with the myometrial function of early postpartum dairy cows.

Chapter 1 introduces the topic by briefly summarizing the events occuring in the puerperal uterus, focusing on the role of myometrial contractions, and listing some of the possibilities used to record uterine contractility. The demand for an accurate, non-invasive, intrauterine pressure (IUP) recording and analysis system, for use in postpartum cows kept on dairy farms, is mentioned - as is the need for more physiological data on uterine functioning after normal parturition.

Chapter 2 reviews the development of techniques for measuring, analyzing and evaluating uterine activity. Changes in IUP during the normal and abnormal bovine postpartum period are detailed in chronological order. Following their previous introduction, the effects of some drugs, used to influence uterine contractility, are reviewed.

Chapter 3 describes the good correlations between the results from two simultaneous electromyographic (EMG) recordings (using surgically imbedded bipolar electrodes), those from two different IUP recording methods (an open tip catheter and a microtransducer system), as well as those from the above IUP and EMG methods, in cows after induced parturition. It outlines a new digital technique for properly characterizing mechanical activity in the early postpartum bovine uterus even under on-farm circumstances, based on low-cost, disposable IUP recording units, which utilize a transcervically introduced, non-invasive method for fixation of the IUP measuring units (the "virtual knot"), and especially developed acquisition and analyzing softwares with a post-measurement filtering capability.

Chapter 4 describes the successful application of a digital non-invasive, open tip catheter system to quantifying IUP changes in untreated, healthy, postpartum cows under on-farm conditions. While showing considerable individual variability, the mean frequency (FREQ), amplitude (AMP) and area under the curve (AUC) values for the myometrial contractions decreased continuously and significantly during the first 48 hours postpartum, with the largest decline occurring between 12 and 24 hours. The IUP values showed no significant correlations with blood Ca2+-concentrations.

Using the above system, the uterotonic effects of a single intramuscular treatment with oxytocin (50 IU) or carbetocin (0.35 mg), 14 to 16 hours after normal parturition, are examined in Chapter 5. These treatments were similarly effective, almost identical in enhancing uterine contractility. In each case, FREQ and total area under the curve (TAUC) showed a significant short-term treatment effect (until 4 h after treatment) - peaking during the 1st post-treatment hour, and returning to the initial levels during the 3rd hour. Other parameters (AMP, DUR /duration/ and AUC) were not affected. None of the IUP parameters revealed any significant effect in the long-term analysis (12 to 36 hours post-treatment) due to any of these treatments.

Chapter 6 details an investigation into oxytocin-induced prostaglandin release - as characterized by plasma 15-ketodihydroprostaglandin-F2α concentrations. Intramuscular treatment with a therapeutical dose of oxytocin (50 IU) between 13 and 15 hours after calving did not significantly alter prostaglandin release. However, administering the oxytocin on two cows intravascularly, did provide evidence of an oxytocin-induced prostaglandin synthesis. It is hypothesized that, although the quantity of released prostaglandins appearing in the peripheral circulation after an intramuscular oxytocin treatment seems to be too small to be detected, it may have an indirect effect through the stimulation of a local prostaglandin synthesis and release, making an additional contribution to the direct uterotonic effect of oxytocin.

Chapter 7 summarizes and generally discusses the previous chapters in the context of the most current knowledge available in the literature, listing the main outcomes and conclusions of the thesis.