Study of mammary blood supply dynamics during milking in dairy cows
In the trial conducted on 9 cows during periods before milking, during milking and 18-min period after milking, blood pressure and volumetric flow rate in the udder were recorded. Udder vascular resistance was assessed by dividing the mean arterial pressure by volume blood flow rate in udder. A positive correlation (r=0.85; P<0.01) was indicated between the value of milk yield and the level of udder blood supply (volume blood flow rate) during the period before milking. A similar relationship was found between heart rate and systemic arterial pressure (r=0.78; P<0.05). Milk output caused by milking was accompanied by an increase in blood supply to the udder while reducing its vascular resistance against the background of constant systemic blood pressure. It is assumed that the increase in volume blood flow during milking is a consequence of reduction of intra-udder pressure coming after milk output from alveols. After the end of milking, the tone of blood vessels of the udder returns to the levels observed prior to milking. In quickly milked cows, there was indicated a more intensive increase in the volume of blood flow rate in the udder and a deeper decline in vascular resistance compared with slowly milked cows.