74 
Journal of Agricultural Research 
Vol. XIV, No. t 
The percentage of butter fat among these 98 tests decreases with age 
as in Table E, as follows: 
Number of 
animals. 
Age. 
Percentage 
of fat. 
19 
Years. 
2 to 3. 
4. 112 
22 
3 to 4. 
4*035 
20 
4 to 5... 
3 * 997 
37 
5 ana over. .. 
3.842 
The work of Speir 1 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 T .—Summary of results from a study of the correlation between the percentage of 
fat and yield of milk for grade Jerseys 
[Eat in percentage; milk in pounds] 
Age. 
Num¬ 
ber of 
animals. 
* 
Type of 
test. 
Mean. 
Standard 
deviation. 
Coefficient 
of 
variability. 
Correlation, 
Years. 
a to 3. 
3 to 4. 
4 to s. 
5 and over. 
xoi.... 
155- 
146.. .. 
348 .. .. 
/Milk. 
\Fat. 
/Milk. 
\Eat. 
\Fat. 
/Milk. 
\Fat. 
4*663.5 ±81.7 
5. io6± 0.033 
5 * 035*5 ± 7 i *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 
o-489± 0.023 
1,316.0 ±50.4 
0. 592 ± 0.023 
1,281.5 ±50.6 
O. 520± 0.021 
1,329.0 ± 34*0 
0.6o6± 0.016 
26. ioi 1.32 
9 - 57 ±o .45 
26.13 ±1.07 
II- 56dho. 45 
24.19±I-OI 
xo. a6±o. 41 
24. i4±o. 65 
12. 32±o-32 
j—0.114 ±0-066 
>—0. 234± 0.051 
>—0. 272±0.05* 
}—0. I 38 ±o.Q 3 S 
1 Speir, John, miiok records. In Trans. Highland and Agr. Soc. Scotland, s. 5, v. 16, p. 170-229, fig. 
18-20. 1904. 
