July 8, 1918 
Percentage of Fat in Cow's Milk 
71 
and those yielding 9,500 to 13,000 pounds of milk, and finding the aver- 
age yield of milk and percentage of fat. The decrease from 5.657 per 
cent for the first group to 4.941 per cent for the third group is very sig- 
nificant. Any group of cows showing a negative correlation betv/een 
percentage of fat and yield of milk would give, in general, the same 
results if treated as was Table II. 
Table B. — Milk yield and percentage of butter fat of ferseys 3 to 4 years of age 
Number of animals. 
Extremes of milk 
yield. 
Average milk 
yield. 
Average per- 
centage of fat. 
Pounds. 
Pounds. 

4, 500- 6, 500 
6, 049. 3 
5-657 
220 
7, 000- 9, 000 
7,677. 3 
5- 307 
39 
9. S°o-i3) 
10, 307. 7 
4. 941 
GUERNSEY 
Tables VI to IX show the distribution of individuals with regard to 
the yield of milk and the percentage of butter fat, in the form of correla- 
tion tables. Table X combines Tables VI to IX. Table C gives 
the means, standard deviations, coefficients of variability of milk and fat, 
and the correlation between the percentage of fat and yield of milk for 
Guernseys of different ages. 
Table C. — Summary of results from a study of the correlation between the percentage 
of fat and yield of milk for Guernseys 
|Fat in percentage; milk in pounds) 
» 
Age. 
Num- 
ber of 
ani- 
mals. 
Type of 
test. 
Mean. 
Standard 
deviation. 
Coefficient 
of 
variability. 
Correlation. 
Years. 
2 to 3 
3 to 4 
4 to 5 
5 and over 
All ages 
i>375 
644 
478 
I, 067 
3>S64 
(Milk 
\Fat 
/Milk 
\Fat 
/Milk 
\Fat 
/Milk 
\Fat 
(Milk 
IFat 
7, 608. 0 ± 28. 8 
5. 065J1 0.008 
8,317.0 ±49.3 
5. o8o± 0. 013 
9,247.0 ±62.6 
5. 046 ± 0. 014 
9,893.0 ±42.8 
4. 956± 0. 010 
8,644.4 ±23.7 
5. 033± 0.005 
1 . 584. 0 ± 20. 4 
0. 458± 0. 006 
1,854.0 ±34.8 
0. 477 ± 0. 009 
2,030.0 ±44.3 
0. 462 ± 0. 010 
2,067.5 ±30.2 
o. 4781b 0. 007 
2,095.4 ±16.7 
0. 471 ± 0. 004 
20. 82±o. 77 
9- O3±o. 32 
22. 29±o. 44 
9- 39±o. 18 
21. 95±o. 50 
9. 13 ±0. 20 
20. 90±o. 68 
9. 64±o. 30 
24. 24±o. 20 
9. 35±o- 08 
|— 0. 25i±o. 017 
\ — 0. 289 ±0. 024 
>— 0. 264±o. #29 
|— 0. 337±o. 018 
|— 0. 296±o. 010 
The correlation coefficients are negative as in the case of the Jerseys, 
but slightly smaller. For the Jerseys they range from —0.359 ±0.040 to 
— o.437±o.o27, while for the Guernseys the range is from —0.251 ±0.017 
to —0.337 ±0.01 8. The yield of milk gradually increases from an aver- 
age of 7,608 pounds for the 2-to-3-year-old class to 9,893 for the group 
which is 5 years and over. The average percentage of fat varies from 
4-956± 0.010 for the group which is 5 years and over to 5.o8o±o.oi3 for 
the 3-to-4-year-old class. (See fig. 2.) 
