598 
Joumal of Agricultural Research 
Vol. XXIX, No. 12 
Table IV .—Calculated values of Kt for Holsteins and Jerseys from cow-testing 
association and advanced registry records 
Num- 
Pounds nutrients for— 
Records 
ber of 
records 
Milk 
Fat 
Weight 
1 
Lacta- ! Mainte- 
tion | nance 
Total 
Kt 
Holstein C.T.A__ 
2,773 
970 
5,266 
Pounds 
7, 218 
5,364 
14,887 
Per cent 
3.54 
Pounds 
1,038 
925 
1,150 
861 
2,193 j 3,001 
2,050 ; 2,674 
4,428 ; 3,324 
3,165 2,489 
5,194 
0.116 
Jersey C.T. A__ 
Holstein A. R_ 
5.14 
3.41 
4, 724 
7, 752 
5, 654 
.113 
.086 
Jersey R. M _ 
S, 038 
8 ; 005 
5. 41 
.087 
The milk yields and fat percentages are 
from .data by Gaines and Davidson 
( 8, p. 619); the weights for the 
advanced registry records are from 
Table III; the weight for the Holstein 
C. T. A. records is the average of 793 
cows included in the total (2,773); and 
the weight for the Jersey C. T. A. 
records is an estimate based on personal 
observation of the cows concerned. 
It will be noted from Table IV that 
the values of K T for Holstein and 
Jersey cows from the cow-testing asso¬ 
ciation records are very nearly the 
same, 0.116 and 0.113, respectively. 
The value of the constant, Kt , corre¬ 
sponds to the theoretical pounds of 
nutrients required per unit of energy 
value (49.64 large calories) of the milk 
solids. Kt is virtually an inverse index 
of cow efficiency. The breeding and 
conditions of management of the cows 
concerned here are quite comparable. 
A large proportion (about 90 per cent) 
of the cows were high grades and the 
balance purebreds. The feeding and 
management were those of good com¬ 
mercial practice in the whole-milk dis¬ 
tricts of Illinois. It is quite probable, 
as will be shown later, that the calcu¬ 
lated value of K t under these condi¬ 
tions is very close to the actual value. 
Compared with the records of the 
cow-testing association, the advanced 
registry records show a lower calcu¬ 
lated value for Kt, namely, 0.086 for 
the Holstein and 0.087 for the Jerseys. 
But, again, under the conditions of 
official testing, the values for the two 
breeds are practically equal. . The 
lower value of Kt is due to the higher 
level of production. Since many of the 
records included here are the result of 
deferred breeding and continuous milk¬ 
ing throughout the year as well as 
extravagant feeding, the indicated 
values of Kt do not represent practical 
commercial milk production. 
The point of immediate interest, 
however, is whether the relation 
N t =Kt (2.66 + 0 holds as between 
breeds. While the evidence is not as 
precise as may be desired, it does 
indicate so far as it goes that the 
relation holds reasonably close between 
breeds. 
FEED COST IN DOLLARS 
Feed cost in nutrients may be trans¬ 
lated into feed cost in dollars by deter¬ 
mining the price of nutrients in 
the feeds used. There is very little 
difference in the character of the ration 
required for milk production so far as 
affected by fat percentage of the milk. 
The lower-testing cow requires a 
slightly greater proportion of protein 
but that the effect of this difference on 
cost per pound of nutrients is quite 
negligible may be inferred from data of 
Ross, Hall, and Rhode (7). They show 
the cost per pound of nutrients (pasture 
not included) to be nearly constant so 
far as affected by yearly fat yield of the 
cow. Thus, as the yield of fat increased 
from 161 to 361 pounds, the cost per 
pound of nutrients in the feed con¬ 
sumed increased by less than 3 per 
cent, as an average of the five years 
1908 to 1912. 
From this it seems safe to assume 
that the cost per pound of nutrients is 
practically unaffected by the fat per¬ 
centage of the milk. Hence, feed cost 
in dollars is proportional to feed cost 
in nutrients, and so far as affected by 
percentage fat content of the milk 
FC=K (2.66 + f) 
in which FC is feed cost ($) per pound 
of milk; t is per cent of fat in the milk; 
and K is a constant dependent in value 
on the price level of feeds and on the 
value of K t . 
While the point under consideration 
here is relative costs, rather than 
absolute costs, it is perhaps worth 
while to draw a comparison as to 
absolute feed cost. Pearson (6), by 
cost accounting methods, found the 
cow feed cost of milk production to be 
$1.05 per hundredweight of milk for 
