50 Maine Agricultural Experiment Station. 1920. 



a pound for each such day to the 250.5 pounds required when 

 two years old. This ratio of increase applies until the cow is 

 five years old at the beginning of her test, when the required 

 amount will have reached 360 pounds, which will be the amount 

 of butter-fat required of all cows five years old or over. These 

 standards are based upon one complete year's record from the 

 time of beginning, regardless of any time which may be lost by 

 being dry or calving during the period." Three facts are obvi- 

 ously true of the Jersey Registry of Merit cows as compared 

 with a true sample taken at random of the milking cows of the 

 Jersey breed; (1) the cows making up the Registry of Merit 

 are a selected sample; (2) the scale of the selection is linear 

 having its lower limit 250.5 pounds of butter-fat production at 

 2 years and its upper limit 360 pounds at 5, years and over; 

 (3) this requirement means that for each day of age at test 

 the frequency distributions of years production are cut off 

 perpendicularly at the requirement and only those animals mak- 

 ing greater yields than this are allowed to be entered into the 

 Registry of Merit. The data taken from this Registry of Merit 

 are not the true data for the Jersey breed and conclusions based 

 on it cannot be considered as applying to the breed as a whole 

 or to the general problems of milk secretion. 



To supply this need of exact data on the Jersey breed as a 

 whole the Maine Agricultural Experiment Station has obtained 

 the recorded data of one of the largest pure bred Jersey herds 

 known. The data are exceptional in the following ways : ( 1 ) 

 The records extend back to the year 1897 when the herd was 

 organized; (2) the animals are practically all straight island 

 stock; (3) they have been under the oversight and direction 

 of one manager since 1901 ; (4) exact records are kept of the 

 milk production, butter-fat and butter-fat per cent; (5) many 

 of the individual animals have records for several different 

 lactations. The elimination of variation of the milk production 

 of cows or groups of cows caused by changes in any one or 

 more of these five factors is important for the analysis of the 

 causative mechanism of milk and butter- fat production. It is 

 obvious that these records are free from such variables. They 

 •constitute a homogeneous group of data representing the island 

 Jersey under constant conditions of management and climate. 



