Studies in Milk Secretion 91 



ing of the accuracy of the records. The precautions taken 

 should make this body of data quite accurate. 



Most of these records contain the following information 

 about each cow which has made the Registry of Merit require- 

 ments in the test. The Registry of Merit number, name and 

 herd book number of the cow is given. The pedigree record 

 includes the name and number of the sire and dam of the cow 

 tested. The record includes the amount of milk, the percentage 

 of butter-fat, the amount of butter-fat, the age at test, the 

 length of the record and the time at which the record was made. 



Methods. 



In this investigation was included every bull having two 

 or more daughters with year records in the Registry of Merit 

 volumes I to V when the dams of these daughters also had year 

 records. The reason for not including those bulls with only 

 one daughter was the great variation which such records would 

 take through the influence of chance alone. This variation is 

 seen in table III to be a very considerable quantity when two 

 or more records are considered. It would, of course, be much 

 higher for records based on only one daughter, in fact becom- 

 ing so great that little or no reliance could be placed in such 

 a record as a measure of the bull's capacities as a breeder. 



Laws Governing the Changes in Milk Flow and Butter- 

 Fat Percentage with Age in Jersey Registry of 

 Merit Cattle. 



Several papers from this laboratory (7, 11) have dealt 

 with the variation of milk at different ages in the life of the 

 cow. In these studies a correlation of considerable size has 

 been shown between milk production and age at test when this 

 correlation is measured by the correlation ratio. It has been 

 further shown that the regression of milk production on age is 

 by no means a linear regression; in point of fact the regression 

 is logarithmic. 



These considerations make it necessary to correct each milk 

 record to a standard age before any just comparison may be 

 made between the milk production of the daughter and that of 

 her dam. For this correction 2153 year records were extracted 



