76 Journal of A gricultural Research voi. xiv. No. » 
the group 5 years of age and over in the Jerseys and Guernseys shows a 
shghtly 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 
(7) The average percentages of fat for the different breeds are as 
follows (see Table XXI.) 
XXI.) 
Pounds. 
Holstein-Friesian 
Ayrshire 
Guernsey 
Jersey 
14, 443- I 
9, 417. I 
8,644.4 
7. 491- 4 
Pounds. 
Jersey 
Guernsey 
Ayrshire 
Holstein-Friesian 
5- 392 
5-033 
3-933 
3-435 
