Allen: Effect of Parents' Age on Quality of Dairy Cows 169 



Group II All cows producing be- 

 tween 25.6 and 27. 3 pounds of butter- 

 fat in 7 days. 



Group III All cows producing be- 

 tween 24 . and 25 . 6 pounds of butter- 

 fat in 7 days. 



The comparatively inferior class of 

 animals chosen includes all of the so- 

 called mature cows, that is, cows five 

 years of age or over, that produced 

 less than fourteen pounds of butter- 

 fat in seven days and were entered in 

 the 27th Volume of the Holstein Frie- 

 sian Advanced Registry Year Book as 

 entries or re-entries. This class was 

 divided into three groups that were 

 fairly comparable in numbers to the 

 groups of the superior class, as follows : 



Group I All cows producing be- 

 tween 12 and 12.5 pounds of butter- 

 fat in 7 days. 



Group II All cows producing 

 between 12.5 and 13.0 pounds of 

 butterfat in 7 days. 



Group III All cows producing be- 

 tween 13.0 and 14 . pounds of butter- 

 fat in 7 days. 



The groups were arranged so that 

 the very highest producers were in 

 group 1 of the Superior Class and 

 the very lowest producers were in 

 group 1 of the Inferior Class. Then, 

 if there was any difference in age, 

 it was thought that the first groups 

 should be further apart than the second 

 and third groups. 



The 7 day record was chosen as the 

 basis for this study because a larger 



number of records were available and 

 the 7 day record is generally recog- 

 nized as a valuable method of deter- 

 mining the productive ability of dairy 

 cows. 



Three generation pedigrees were 

 compiled for all the cows of both the 

 Superior and Inferior Classes. These 

 pedigrees included the date of birth 

 for all animals in every pedigree. This 

 makes it possible to compute the dif- 

 ference in age between any animal and 

 its parents and tells us the age of the 

 parents at the time the animal in 

 question was born. This also provides 

 data for determining the average differ- 

 ence in age between generations, and 

 allows the calculation of the percentage 

 distribution of offspring according to 

 the age of parents, making it possible 

 to observe whether more good cows 

 or poor cows are born from very young 

 or very old dams. The difference in 

 age between parent and offspring was 

 computed in months to the nearest 

 month. 



In order to determine at what age 

 the superior cows made their records, 

 it was necessary to take this data 

 directly from the Advanced Registry 

 Year book and record it on the pedi- 

 gree. 



RESULTS THE DIFFERENCE IN AGE 



COMPARED 



Table I gives the average age of the 

 ancestry of the Superior and the Infer- 

 ior Classes by groups and for the classes 



TABLE I. Average Age, in Months, of Ancestry of Superior and of Inferior Classes of Cows 



1 Great grand sire refers to sire of paternal grand sire. Great grand dam refers to the dam of 

 the maternal grand dam. 



