OS 4 



THE AMEBIC AN NATURALIST 



[Vol.L 



from the means of the classes. (See average per cents, 

 of class means, Table V.) A similar condition obtains 

 with the age classes after ten years. It would appear 

 from this that mature cows give milk slightly richer than 

 immature cows, or than old cows past 10 years of age. 



A rather peculiar condition with reference to the fat 

 production curve is shown in the mean results of the 

 half-year ages up to the 6^-year class. Each half-year 

 class advances but slightly, if at all, from its preceding 

 year class, then there is a sudden drop to the next full- 

 year class. The milk production curves indicate the same 

 condition, though to a lesser extent, and as previously 

 noted, the frequencies in these half-year classes are not 

 more than 60 per cent, of the full-year classes. No good 

 explanation is offered for this. It might be inferred that 

 a cow freshening at 2^ years is not much better able to 

 withstand the strain of milk production than a 2-year-old, 

 and that this condition continues. However, in many re- 

 spects this theory does not appear sound. 



Attention is called again to the points of curve 4 for 

 fat production given in Table IV. This curve is plotted 

 for the purpose of showing what the requirements ought 

 to be according to the performance of cows that have 

 made records. The animals involved in this curve repre- 

 sent 45 per cent, of all the A.R.O. records that had been 

 made up to the time of publication of Vol. 24, hence the 



TABLE V 



