Animal Husbandry Investigations in 1919. 253 



is, however, fairly closely proportional to the breed's milk yield 

 at eight years. Such being the case it follows that the relative 

 physiological effect of age on milk production of the different 

 breeds is the same. 



Should this be granted it follows that the results for milk 

 yield determined for one breed will probably be correct for an- 

 other breed insofar as this age effect is concerned. 



Age at which the Cows of the Different Breeds Reach 

 Maturity or Maximum Milk Production. 



Some interest is attached to the age at which the different 

 breeds reach their maximum productivity. This question may 

 be answered insofar as it related to advanced registry data. 

 From the equation to the curves given above it is possible by 

 differentiation to determine the age at which maximum yield 

 occurs. When this is so determined the results are : 



Holstein-Friesian maximum milk yield occurs at 8 years, 



4 months, 29 days. 



Guernsey maximum milk yield occurs at 9 years, 8 months, 



5 days. 



Jersey maximum milk yield occurs at 8 years, 1 month, 13 

 days. 



These ages at maximum milk yield show that the Jersey 

 reaches this yield before any of the other breeds. Closely fol- 

 lowing this breed is the Holstein-Friesian with the maximum 

 milk yield at 8 years, 4 months and 29 days. The Guernsey is 

 the last breed to reach its maximum yield. This breed reaches 

 this yield at 9 years, 8 months and 5 days. In consideration of 

 these maximum yields it should be remembered that for some 

 time prior to and after the age at which the maximum yields of 

 milk occurs the cow is giving nearly this amount of milk. Fur- 

 ther than this milk production in itself is highly variable. All 

 these fluctuations taken into account the close agreement be- 

 tween these ages of maximum productivity for the breeds is 

 rather surprising. 



