Julys, 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 Holslein-Friesians 
• [Fat in percentage; milk in pounds] 
Age. 
Num- 
ber of 
animals. 
Type of 
test. 
1 
1 Standard 
Mean. 1 deviation. 
i 
Coefficient 
of 
variability. 
Correlation. 
Years. 
» to 3 
3 to 4 
4t05 
5 and over 
76 
88 
41 
136.... 
aiilk 
\Fat 
/Milk 
\Fat 
/Milk 
\F3t 
/Milk 
IFat 
5,776.5 ±113-4 
3.688± 0.028 
6,727.5 ±112.1 
3.S6S± 0.02s 
7,303-0 ±214-8 
3.58i± 0.041 
7,441.0 ±104. 1 
3.546± 0.02s 
1,465.5 ± 80.2 
0. 36l± 0-020 
1,559.0 ± 79-3 
0. 344± 0.018 
2,039.5 ±151-9 
0. 39l± 0.029 
1,799.0 ± 73-6 
0. 440± 0.018 
25-37±i-48 
9. 8o±o. 54 
23. I7±i- 24 
9. 64±o. 49 
27.92±2- 2i 
10. 92±o. 82 
24. i8± I. OS 
I2.39±o. SI 
> — 0. 2II±0. 074 
|-o.34S±o.o6i 
|— 0. i33±o. 103 
|— 0. 2I2±0. 053 
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. 
Nimi- 
ber of 
animals. 
Type of 
test. 
Mean. 
Standard 
deviation. 
Coefficient 
of 
variability. 
Correlation. 
All ages 
2, 002 . . 
/Milk 
\Fat 
5,824.6 ±28.5 
3.902± 0.009 
1,888.2 ±20.1 
0. S75± c. 006 
32.42±o.38 
14. 75±o- 16 
|— o.359±o. 013 
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 XX I 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 ^ showed 
that in Jersey cows using the 7-day records that the maximum produc- 
tion is reached between the eighth and ninth year. Crowther ^ from 
records of Ayrshires is of the opinion that maximum production is close 
to the eighth year. (See Table XXI and fig. i.) 
(3) In the Jerseys, Guernseys, and Holstein-Friesians the percentage 
of fat remains fairly constant for the different ages studied. However, 
' Peari,, Raymond, and Patterson, S. W. the change op milk flow with age, as determined 
VROM the seven-day records OP JERSEY COWS. Maine Agr. Exp. Sta. Bui. 262, p. 145-152, fig. 7. 1917. 
'Crowther, Charles. v.\riation in the composition op cow's milk. In Jour. Agr. Sd., v. i, pt. 2, 
p, 149-175- 1905. 
