Bruckmaier R M, Schams D, Blum J W
Institut für Tierzucht, Universität Bern, Schweiz.
J Dairy Res. 1994 Aug;61(3):323-34. doi: 10.1017/s0022029900030740.
The importance of elevated concentrations of oxytocin (OT) during the entire milking period was investigated in seven primiparous dairy cows with inherent disturbed milk ejection and in sixteen healthy cows with disturbed milk ejection induced by placing them in an operating theatre. Disturbance of milk removal in both groups has previously been demonstrated to be exclusively due to central blockage of the expected OT release in response to teat stimulation and milking. However, milk ejection can be induced by exogenous OT. OT (0.2 i.u.) was injected i.v. before milking and 49 +/- 6% of the total milk was removed. When plasma OT decreased, milk flow stopped. In response to a second and third injection of 0.2 i.u. OT, 30 +/- 4 and 7 +/- 2% of the milk were removed respectively. The remaining milk was removed with 10 i.u. OT. The lag time from injection of OT to the start of milk flow was inversely correlated with the amount of milk actually removed in response to the OT injection. If 0.2 i.u. OT was injected during intramammary pressure (IMP) recording, IMP immediately increased to its maximum value. After 2.5 +/- 0.3 min, IMP decreased to an intermediate IMP (between preinjection and maximum IMP). After two additional injections of 0.2 i.u. OT and after injection of 0.5 i.u. OT, IMP increased to a similar maximum. However, after injection of 0.5 i.u. OT, maximum IMP lasted longer (2.9 +/- 0.3 min; P < 0.05) than after injections of 0.2 i.u. If OT was continuously infused (0.15 i.u./min) during milking, milk flow lasted until the udder was completely emptied. IMP increased during OT infusion to a maximum which remained stable until infusion was stopped after 10 min. The same IMP maximum was reached after the first individual OT injection (0.2 i.u.), but when plasma OT decreased towards basal concentrations, milk flow ceased and IMP decreased to an intermediate level. Thus continuously elevated OT concentrations such as those during infusion or during normal milking are necessary for complete milk removal.
在7头初产奶牛（其本身存在乳汁排出障碍）和16头健康奶牛（通过将其放置在手术室诱导产生乳汁排出障碍）中，研究了整个挤奶期间催产素（OT）浓度升高的重要性。先前已证明，两组的乳汁排出障碍完全是由于对乳头刺激和挤奶预期的OT释放受到中枢性阻断所致。然而，外源性OT可诱导乳汁排出。在挤奶前静脉注射OT（0.2国际单位），挤出了49±6%的总乳汁。当血浆OT下降时，乳汁流动停止。在第二次和第三次注射0.2国际单位OT后，分别挤出了30±4%和7±2%的乳汁。剩余乳汁用10国际单位OT挤出。从注射OT到乳汁开始流动的滞后时间与注射OT后实际挤出的乳汁量呈负相关。如果在记录乳房内压（IMP）期间注射0.2国际单位OT，IMP立即升至最大值。2.5±0.3分钟后，IMP降至中间值（介于注射前和最大IMP之间）。在额外两次注射0.2国际单位OT以及注射0.5国际单位OT后，IMP升至类似的最大值。然而，注射0.5国际单位OT后，最大IMP持续的时间（2.9±0.3分钟；P<0.05）比注射0.2国际单位OT后更长。如果在挤奶期间持续输注OT（0.15国际单位/分钟），乳汁流动会持续到乳房完全排空。在OT输注期间，IMP升高至最大值并保持稳定，直到10分钟后停止输注。第一次单独注射OT（0.2国际单位）后也达到了相同的IMP最大值，但当血浆OT降至基础浓度时，乳汁流动停止，IMP降至中间水平。因此，持续升高的OT浓度，如输注期间或正常挤奶期间的浓度，对于完全挤出乳汁是必要的。
