Williams D M, Mein G A
Milking Research Centre, Institute of Dairy Technology, Werribee, Victoria, Australia.
J Dairy Res. 1987 Aug;54(3):321-5. doi: 10.1017/s0022029900025498.
The magnitude of the forces causing closure of the bovine teat canal was estimated by measuring the pressure required to cause retrograde flow of milk into the canal from a manometer attached to the external teat orifice. Before milking, the hydrostatic pressure required to cause retrograde flow was 12 kPa or greater. Retrograde flow occurred at a pressure of 4-6 kPa once the teat canal surface had been wetted. This 2- or 3-fold fall in the closing forces presumably resulted from the combined effects of fracturing the teat canal epithelium and loss of initial resting tension in the smooth muscle fibres surrounding the teat canal. After milking, retrograde flow into any teat canal occurred at a pressure approximately 1 kPa lower than the wetted, pre-milking value. This small drop, and subsequent recovery approximately 30 min after milking, reflects the change in tonicity of the smooth muscle fibres which are stretched during milking. At hydrostatic pressures below 7-9 kPa, retrograde flow could be arrested momentarily by the occurrence of a teat contraction. At 4-7 kPa, the wave of contraction was also capable of expelling 4-14 microliters milk from the teat canal indicating the outwardly directed, peristaltic nature of the phasic muscular activity.
通过测量连接到乳头外口的压力计使牛奶逆行流入乳头管所需的压力，估算导致牛乳头管闭合的力的大小。挤奶前，导致逆行流动所需的静水压力为12kPa或更高。一旦乳头管表面被浸湿，在4-6kPa的压力下就会发生逆行流动。这种闭合力下降2倍或3倍，可能是乳头管上皮破裂和乳头管周围平滑肌纤维初始静息张力丧失的综合作用所致。挤奶后，任何乳头管的逆行流动发生时的压力比浸湿的挤奶前值低约1kPa。这种小幅度下降以及挤奶后约30分钟的随后恢复，反映了挤奶过程中被拉伸的平滑肌纤维张力的变化。在低于7-9kPa的静水压力下，乳头收缩的发生可使逆行流动暂时停止。在4-7kPa时，收缩波也能够从乳头管排出4-14微升牛奶，表明阶段性肌肉活动具有向外的蠕动性质。
