Table 3— SECRETION OF 87¢s AND POTASSIUM IN MILK FROM HOLSTEIN COWS*
IN RELATION TO STAGE OF LACTATION, PREGNANCY, AGE, AND LEVEL OF
PRODUCTION
ak /feed rati
Stage
Stage
of
of
Cow lactation, pregnancy,
days
days —
No.
Age,
years
Level of
/
Milk/tee
atios
production,
liters/day
''Cs,%
of intake
Transfer
coefficient?
Potassium, %
of intake
507
29
0
5.6
28.4
14.8
0.0052
16.1
509
35
()
5.4
33.3
14,2
0,0043
21.0
505
49
0
5.6
32.5
13.1
0.0040
19.1
572
509
61
72
0
0
5.5
19.8
34.0
&.1
11.0
0.0041
0.0032
9,1
17.1
521
1
509
532
50
75
93
98
98
108
0
0
20
0
41
5.4
5.1
5.6
5.4
4.4
26.2
31.1
31.4
34.6
27.1
7.2
14.5
7.6
16.4
7.6
0.0027
0.0047
0.0024
0.0047
0.0028
14.2
14.8
14,7
23,5
521
532
521
532
572
110
134
138
161
167
6
8
33
35
80
5.5
5.5
5.6
5.6
7.9
20.8
25.4
23.2
29.6
14.1
&.5
9.4
9.8
9,2
5.8
0,0041
0,0037
0.0042
0.0031
0.0041
13.3
16.2
12.9
15.6
7.8
572
572
86
532
599
203
230
232
248
328
116
142
0
161
97
8.0
8.0
8.3
5.4
8.0
11,2
9.4
8.4
7.5
5.7
4.3
3.8
2.8
2.7
2.1
0.0038
0.0041
0.0033
0.0036
0,0037
5.2
4,2
4.4
3.9
2.5
Mean
0.0038
11.0
*The ration for all cows consisted of approximately 10 kg of alfalfa hay and 5 kg of
mixed grains.
7As defined in text.
fields. A mean value for this transfer coefficient* was found to be
0.0038 with a standard deviation of 0.0008 for a group of 10 Holstein
cows that were fed what is considered an average diet for dairy cattle
(Table 3). In this group of cows, the amount of milk produced per day
varied widely as did the percentage of total "Cs secreted per day in
the milk. However, when the results were expressed as a transfer coefficient, the variation was greatly reduced, although the range in values
still varied by a factor of 2 (0.0024 to 0.0052). The percentage per liter
thus appears to be relatively constant and in an average diet amounts
to about 0.33% of the total *"Csintake. Limited data from our laboratory
indicate
that
low-milk-producing
cows
excreted a proportionately
higher percentage of 37Cs in the urine than did high- milk-producing
cows. These data mean that the level of production for the dairy herds
supplying a milk shed would be of little importance in explaining varia-
tions in the '°"Cs level in milk.
*Transfer coefficients were calculated by dividing the "Cs content of milk
in picocuries per liter by the total daily intake of ¥"’Cs in feed in picocuries.