240 



Bulletin 397 



Pearl and Patterson (19 17) have shown that the maximiim seven-day 

 milk production of Jersey cows is reached between eight and nine years 

 of age. Miner (191 5) has shown that the maximum seven-day fat pro- 

 duction of Holstein cows is also reached between eight and nine years 

 of age. Both these studies were made with seven-day records. The larger 

 number of individuals used gives a smoother curve and greater certainty 

 to the results. The curve presented in this bulletin shows that maximum 

 production for a whole lactation was reached during the eighth lactation, 

 which corresponds to an age of from nine to ten years. The close agree- 

 ment of these results of yearly records for a few cows, with seven-day 

 records for larger numbers tends to substantiate the former. Probably 

 maximum production is reached somewhat later in life than is ordinarily 

 supposed. 



The curves (fig. 60) showing the relation of age to fat production agree 

 very closely with those for milk production. 



In studying the relation of the production of a cow for her first lactation 

 to the production for her lactation of maximum production, the difficulty 

 has been in finding out which is the lactation of maximum production. 

 The foregoing study indicated that the maximum production of these 

 cows was reached during the eighth lactation. As already stated, only 

 fourteen cows had completed eight lactations and therefore the results 

 are not so trustworthy as is desirable. The averages for the fourteen cows 

 for eight lactations are given in table 17: 



TABLE 17. Relation of Age to Milk Production 

 (Averages of 14 cows for 8 lactations) 



For purposes of comparison the averages of sixty cow^s for five lacta- 

 tions are given in table 18. The data indicate that these cows had not 

 yet reached their maximum. 



350 



