116 ILLINOIS ACADEMY OF SCIENCE 



TABLE 7— COEFFICIENTS OF DIGESTIBILITY OF DRY SUBSTANCE 



Period Maintenance One third Two-thirds Full Feed 



Lot Feed Lot Feed Lot Lot 



1 69.29 65.91 63.84 62.55 



2 77.73 71.88 68.82 64.68 



3 78.74 75.80 73.61 69.68 

 4 1 79.56 76.90 75.04 76.01 



includes only 25th to 30th week. 



TABLE 8— COEFFICIENTS OF DIGESTIBILITY OF DRY SUBSTANCE IN 



PERIODS 3 and 4 



J 25th to 37th week except in cases of those steers which were removed from the 

 experiment before the 37th week. 



A STUDY OF THE RELATIVE RELIABILITY OF 

 OFFICIAL TESTS OF DAIRY COWS 



W. W. Yapp, University of Illinois 



To those who are familiar with the dairy industry, I need 

 not point out that, during the past twenty years, there has 

 been a significant increase in the United States, both in respect 

 to the number of milch cows and to the amount of milk and 

 butterfat produced. But out of all proportion to this increase 

 has been the increase in advanced registry testing, or the con- 

 ducting of official tests for ascertaining the milk and butter- 

 fat production of pure-bred cows. In the few moments which 

 I have to speak I cannot even touch upon the extent of this 

 increase or upon the factors which have tended to bring about 

 this growth, but I must begin directly with the discussion of 

 the relative reliability of these tests. 



I shall not attempt to report on my findings except with re- 

 gard to two tests, the seven-day test and the semi-official test. 

 These tests as studied apply only to the Holstein-Friesian 

 breed of dairy cattle. Briefly stated, the seven-day test is an 

 official test, which means that the supervisor or tester weighs 

 and tests the milk of each milking separately, being present at 



