The Effect of Increasing the Negative Pressure and Widening of the Vacuum-Release Ratio on the Rate of Removal of Milk from the Udder

Abstract

Rates of milk withdrawal under varying negative pressures and pulsation ratios (relative time of release and vacuum application) were ascertained on 12 cows by taking scale readings every 10 sec. during the milking. Rates of milk withdrawal were ascertained for 1 minute at the height of milking, the first 3 min. and up to the end point[long dash]the point when not over 0.3 lbs. of milk was obtained in 3 consecutive 10-sec. scale readings. Observations were made on pulsation ratios of 1:1, 1:2 and 1:3 and on negative pressures of 10, 12, 12.5, 14, 15 and 16 inches Hg. Each increment in negative pressure increased the rate of milk withdrawal but not at uniform rates for all cows. Widening the pulsation ratio also increased milk withdrawal but tended to produce congestion of the teats. In a series where increased negative pressures and widening of the pulsation ratios were combined there was a smaller % increase in milk withdrawal rates than for each separately. The variability in rates of withdrawal of milk with negative pressure increments, or widening of the pulsation ratios between cows, or for the same cow, is explained upon the basis of variations in the strength of the meatus muscle and the maximum opening of that orifice.