CHAPTER XV 

 Permanence of Milk Yield and Butter-fat Percentage 



It would be futile to study the inheritance of milk yield or to 

 make Advanced Registry records if two major easily determined 

 facts were not true: First, a record on one lactation should predict 

 with reasonable certainty what the record in a subsequent lactation 

 will be; second, as a corollary to this, a cow's milk record of one 

 lactation should occupy the same relative position among the rec- 

 ords of her herd companions that it does in another lactation. 

 To test the accuracy with which these results follow from a study 

 of cattle records the following tabulation of data is suggested (see 

 pages 95-98). 



Take the data of the college cows preferably using the lactation 

 record of a definite length, for all cows having two or more lacta- 

 tions. Arrange the data so that all cows have records at two years, 

 three years, and four years. Take the records of the cows at two 

 years and arrange them in order of milk yield. Divide the group 

 into as nearly four equal parts as possible, the first part to include 

 the highest producing fourth of the cows, the next group the second 

 highest producing fourth of the cows, the next group the third highest 

 producing fourth of the cows, and the fourth group the lowest 

 producing fourth of the cows. Calculate the average production 

 of each group. Without changing the four groups calculate the 

 average milk yield of each group for the same cows at three years of 

 age and at four years of age. Plot the line showing the average 

 production of the highest group, the second highest, the third highest 

 and the lowest producing cows. What conclusions do you draw? 



Do the same for the butter-fat percentage. 



Write a short paper on this subject after reading the following 

 references. 



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