62 Report of Departmext of Animal Ixdustry of the 



Woll and Humphrey^ gave the results of a study of the milk- 

 ing machine extending from October, 1906, to July, 1908. 

 Twenty-nine cows were milked for periods varying from 4 to 76 

 weeks. The influence of the milking machine was deduced 

 mainly from the rate of shrinkage as contrasted with other hand- 

 milked cows and this data was checked in a measure by compari 

 sons with the yield of the same cows at corresponding periods 

 of previous lactations when they were hand milked. They con- 

 cluded that " The figures for the average weekly decrease in pro- 

 duction for cows kept under similar conditions as these, except 

 that they were milked by hand, has been found to be identical 

 with these, viz., on the average, 2.9 pounds of milk and 0.12 

 pounds of fat. There is, therefore, no difference between the 

 results obtained by hand milking and the average data given in 

 the table for machine-milked cows." Contrasting the results ob- 

 tained bv machine milkine- with the vields obtained in corre^ 

 sponding periods of lactation from the same cows when milked 

 by hand they say: '^ These results agree so closely that they may 

 be considered identical for all practical pui-poses." 



The main difiiculty in measuring the effect of any method of 

 milking lies in the fact that a cow can be milked by only one 

 method at a time. It has been shown that if the method of milk- 

 ing is changed frequently the change itself becomes a disturbing 

 factor which destroys the value of the comparison. This diffi- 

 culty was reduced but not avoided in the Pennsylvania and Wis- 

 consin experiments by making the periods relatively long. These 

 objectionable results would seem to be minimized by making the 

 lactation period the unit of comparison as was done in the Ne- 

 braska studies. However the use of the lactation period in this 

 way involves the fact that the production of a cow during any 

 period is influenced by a number of factors in addition to the 

 manner in which she may be milked. Assuming that her feed 



1 Woll, F. W., and Humplirev, G. C. The efficiency, economy and physio- 

 logical effect of machine milking. Wis. Agr. Exp. Station Research Bui. 3. 

 1909; also Milking machine experiments. Wis. Agr. Exp. Station Bui. 173. 

 1909. 



