July 8, 1918 
Percentage of Fat in Cow’s Milk 
75 
Table G .—Summary of results from a study of the correlation between the percentage of 
fat and yield of milk for grade Holstein-Friesians 
[Fat in percentage; milk in pounds] 
Age. 
Num¬ 
ber of 
animals. 
Type of 
test. 
Mean. 
Standard 
deviation. 
Coefficient 
of 
variability. 
Correlation. 
Years. 
2 to 3. 
3 to 4. 
4 to S. 
5 and over, 
5 , 776-5 ± 113* *4 
3-688± 0.028 
6,727.5 ±112.1 
3*568± 0.025 
7j 305*0 ±214.8 
3 * 58 i± 0.041 
7,441.0 ±104.1 
3.546 ± o. 025 
1,465.5 ±80.2 
o.36i± 0-020 
r, 559 * o ± 79 * 3 
o*344± 0.018 
3,039.5 ±151*9 . 
o. 39i± 0.029 
1 , 799*0 ± 73*6 
0»440± 0.018 
25 - 37 ±x* 48 
9.80 ±0.54 
23.17±x* 24 
9.64±o. 49 
27.92±2. 23 
10.92 ±0.82 
24. i8±i.o5 
X2.39±o. 51 
—0.2ii±o. 074 
—o* 345 ±0.063 
—o. i$ 5 ±o. 103 
2I2±0* 058 
Table H .—Summary of results from a study of the correlation between the percentage of 
fat and yield of milk for cows unclassified as to breed 
[Fat in percentage; milk in pounds] 
Age. 
Num¬ 
ber of 
animals. 
Type of 
test. 
Mean. 
Standard 
deviation. 
Coefficient 
of 
variability. 
Correlation. 
All ages. 
/Milk. 
5,824.6 ±28.5 
1,888-2 ±20.1 
32.42±0. 38 
o- 359 ±o.oi 3 
2,002.. 
\Fat. 
3.902± 0.009 
0. 575 ± 0.006 
14.75 ±0.16 
There is a very significant negative correlation between the yield and 
percentage of fat for all three classes of cows represented by the three 
foregoing tables (Tables F-H). 
CONCLUSIONS 
(1) A significant negative correlation exists between the percentage 
of fat in cows' milk and the yield for the Jerseys, Guernseys, Holstein- 
Friesians, grade Jerseys, grade Holstein-Friesians, and cows unclassified 
as to breed. The correlation for Ayrshires is not significant in the sub¬ 
groups classed in respect to age, but it is significant when these groups 
are treated as a whole. (See Tables XXI and F, G, H.) 
(2) The yield of milk increases with age. However, since all cows 5 
years of age and over are classed together, it may well be that the yield 
decreases at some period beyond 5 years. Pearl and Patterson 1 showed 
that in Jersey cows using the 7-day records that the maximum produc¬ 
tion is reached between the eighth and ninth year. Crowther 2 from 
records of Ayrshires is of the opinion that maximum production is close 
to the eighth year. (See Table XXI and fig. 1.) 
(3) In the Jerseys, Guernseys, and Holstein-Friesians the percentage 
of fat remains fairly constant for the different ages studied. However, 
1 Pearl, Raymond, and Patterson, S. W. the change or milk plow with age, as determined 
from the seven-day records or Jersey cows. Maine Agr. Exp. Sta. Bui. 262, p. 145-152, fig. 7. 1917. 
* Crowther, Charles, variation in the composition or cow’s milk. In Jour. Agr. Sci., v. 1, pt. a, 
