7G Repoet of Depaetment of Animal Industet of the 



"Not only is there no effect of the change of vacuum shown in 

 the general trend of the milk flow but also there is no evidence of 

 any checking effect even at the time when the changes in vacuum 

 occurred. A comparison of the yield at the fifteen milkings at 

 which the vacuum was raised with that at the last corresponding 

 milkings before the change shows that there was a slight increase 

 in milk flow accompanying the increase in vacuum in the case of 

 Gertie F. No. 2 and Millie D. and a somewhat larger decrease in 

 the case of Ruth. This resulted in an average decrease of 0.1 lb., 

 due to the fact that Ruth was decreasing very rapidly in her milk 

 flow. This slight change in the immediate milk flow in connec- 

 tion with the marked change in vacuum is especially noteworthy 

 since cows respond immediately to any detectable change in their 

 milking conditions and this response almost always takes the 

 form of a decreased milk flow. 



The relation of the vacuum to the milk flow as given in Table I 

 is shown graphically in Graph I, opposite. 



Not only was there no demonstrable effect of the change of 

 vacuum upon the flow of milk but also there were no objectionable 

 local effects upon the cows. It is true that at the close of the 

 milking process with the higher vacuum there was some difference 

 of opinion as to the presence of a slight congestion at the ex- 

 tremity of the teats on Ruth F. Whatever abnormality may have 

 been present passed away within a few minutes leaving no ob- 

 jectionable after effect. 



In considering the bearing of this experiment upon the relation 

 of vacuum to the flow of milk it should be remembered that the 

 test was made upon only three cows. These were late in their 

 period of lactation when they may have been less susceptible to 

 unfavorable influences and they were provided with good fitting 

 teat cups which would reduce any unfavorable influences of the 

 high vacuum. Under such conditions it seems fairly clear that 

 the higher vacuum exerted no measurable influence upon the flow. 



On the other hand it should be remembered that under ordinary 

 dairv^ conditions it is difficult to insure a perfect fit of the teat 

 cup in all cases and any error in manipulation will be exaggerated 



