74 
Journal of Agricultural Research 
Vol. XIV. No. a 
The percentage of butter fat among these 98 tests decreases with age 
as in Table E, as follows: 
Number of 
Percentage 
animals. 
Age. 
of fat. 
Years. 
19 
2 to 3 
4. 112 
22 
3 to 4 
4- 03s 
20 
4 to 5 
3- 997 
37 
5 and over . . . 
3. 842 
The work of Speir ^ shows that there is a slight tendency for the per- 
centage of fat to decrease in Ayrshires after the third year. Both Jer- 
seys and Guernseys of 5 years of age and over show a slight decrease. 
(See Tables A and B.) The mature class of Holstein-Friesian cows, 
however, does not show a decrease (Table C). 
cows NOT PURE-BRED 
The writer thought it would be of interest to see the extent of correla- 
tion between the yield and percentage of fat in cows not pure-bred. 
Grade Jerseys, grade Holsteins-Friesians, and cows unclassified as to 
breed are considered. 
Tables F, G, and H give the results of the study for the different 
classes in the order given above. 
Table F. — Summary of results from a study of the correlation between the percentage of 
fat and yield of milk for grade ferseys ' 
[Fat in percentage; milk in pounds] 
Age. 
Num- 
ber of 
animals. 
Type of 
test. 
Mean. 
Standard 
deviation. 
CoefBcient 
of 
variability. 
Correlatiaa. 
Years. 
2 to 3 
3 to 4 
4 to 5 
5 and over 
lOI. . . . 
15s 
146. . . . 
348.... 
/Milk 
\Fat 
/Milk 
\Fat 
nviilk 
IFat 
/Milk 
\Fat 
4,663.5 ±81.7 
5. io6± 0. 033 
5,035-5 ±71-3 
5- 124± 0.023 
5,298.0 ±71.5 
5. o68± 0. 029 
5,504.5 ±48.1 
4-923± 0.022 
1,217.0 ±57.8 
0. 489 ± 0. 023 
1,316.0 ±50.4 
0. 592± 0.023 
1,381.5 ±50.6 
0. 520± 0. 021 
1,329.0 ±34.0 
0. 6o6± 0.016 
26. io± 1. 32 
9.57*0.45 
26. 13 ± 1. 07 
ii.56±o. 45 
24. 19±i. 01 
10. 26±o. 41 
24. i4±o. 65 
12.32io.32 
|— 0. xz4io.oM 
|— 0. 234io.o5l 
| — 0. 272±0-0S2 
|— 0. i38±o.c«35 
• Speir, John. Mn.K records. In Trans. Highland and Agr. Soc. Scotland, s. 5, v. 16, p. 170-229, fig. 
18-30. 1904. 
