76 
Journal of Agricultural Research 
Vol. XIV, No. 3 
the group 5 years of age and over in the Jerseys and Guernseys shows a 
slightly lower percentage of fat than the younger groups. In the case 
of the Ayrshires, there is a gradual decrease with age. Between the 
youngest and oldest groups there is a difference of 0.151 per cent. (See 
Table XXI and fig. 2.) 
(4) When judged by the standard deviation, age has no influence on 
the variability of the percentage of butter fat. But the class 5 years of 
age and over is more variable in the yield of milk than the younger 
groups. This may occur because of the inclusion in this group of old 
cows whose milk yield has decreased. (See Table XXI.) 
(5) The breed has an influence on the variability of milk yield and 
percentage of fat, using the standard deviation as a basis of comparison. 
For variability in yield the breeds stand in the following order in an 
ascending scale: Jersey, Ayrshire, and Guernsey practically the same, 
Holstein-Friesian. For percentage of fat, the order is: Holstein-Friesian 
and Ayrshire about the same, Guernsey, Jersey. (See Table XXI.) 
(6) For the production of milk the breeds stand as follows (see Table 
XXI.) 
Pounds. 
Holstein-Friesian.. 14,443.1 
Ayrshire. 9,417.1 
Guernsey. 8, 644. 4 
Jersey. 7 . 49^4 
(7) The average percentages of fat for the different breeds are as 
follows (see Table XXI.) 
Pounds. 
Jersey... 5.392 
Guernsey.. 5.033 
Ayrshire.. 3.933 
Holstein-Friesian.. 3- 435 
