The Rate of Machine Milking of Dairy Cows. II. Effect of Vacuum and Pulsation Rate

Eighteen randomly selected slow-milking cows were milked with a nmchine operated at various vacuum levels (10, 12.5, and 15) and pulsation rates (20, 50, and 80) for a 27-day experimental period.The nine treatments were assigned at random at the start of each of the three replications included in the above experimental period.Increasing the vacuum level increased the speed of milking and the effect was greater from 10 to 12.5 than from 12.5 to 15 in.Increasing the pulsation rate increased the speed of milking, but the magnitude of its effect was much less than that of increasing the vacuum.Most of the effect of pulsation on increasing the speed of milking occurred from 20 to 50.Increasing the pulsation rate appeared to be more important at low levels of vacuum than it was at high-vacuum levels.Most of the effects of vacuum and pulsation on increasing milking rate were additive.A few treatment interaction terms were significant.In these cases the increases in milking rate expected, had the effects of vacuum and pulsation been additive, were not obtained as a result of this interaction.Changing the vacuum level or pulsation rate affected the cows differently.In general, increasing the vacuum or pulsation caused greater increases in milking rate, percentage-wise, for the slowest-milking group of cows than it did for the fastest-milking group of cows.It was evident from the studies of Dodd (4), Beck et al. (2), and the authors (8) that a few cows substantially slow up the milking routine.If these cows could be milked faster, it would result in a great time-saving for most dairymen.Smith and Petersen (6), Baxter et al. (1), and Gregoire et al. (5) obtained increased rates of milk flow upon increasing the vacuum level.Smith and Petersen noted considerable cow-to-cow variation in reaction to the increased vacuum.Baxter et al. (1) stated that the vacuum not ouly affected cows differently, but that increased vacuum caused greater increases in peak flow for fast-milking cows than for slow-milking cows.IIowever, neither Baxter et al. (1) nor Whittleston and Verrall (10) obtained a decrease in over-all milking rate as they increased the vacuum, because longer stripping times were required.Whittleston (9) observed that pulsation action was in some cases necessary for stimulation of milk flow, but when the pulsator was stopped after a normal start, the cows continued to milk at a normal rate in most cases.Whittleston and Verrall (10) found no difference in average rate of milking using 21 and 42 or 42 and 84 pulsations per minute and 143~ in. of vacuum.On the other hand, Clough et al. (3) obtained faster milking with each increase in pulsation rate between 20 and 80.None of these experiments was specifically directed at the slow-milking cow problem, nor was any designed to determine the interaction, if any, between