832
HAWLEY AND MARKEE
Milk Activities
In both tests peak activity in the milk from cows was reached in
about two days. During the first test the highest and the lowest activity
levels in the milk produced by individual cows were within a factor of
2. In the second test the difference between the highest and the lowest
levels was about a factor of 5 (see Fig. 10). The reason for this spread,
which is consistent, has not yet been examined.
In the second test all six cows were placed under controlled grazing on hot pasture for two weeks. After this time three of the cows
were removed to corrals and fed stored feed. The other three were allowed to graze the entire pasture without control. After five more days
all cows were placed on cold pasture. Table 2 shows the half-lives of
activity in the milk.
.
Table 2— HALF-LIVES OF
ACTIVITY IN MILK
6
8
28
29
o2
33
2
Oro
Sept. 29 to Oct. 2
Hw OO Hm
8
a2
53
CFF
Sept. 22 to 26
107
29
OPO
6
28
tO UI GO
T,, days
NWmrwonp-+70
sept. 17 to 20
Cow No.
wom4ndnnwrh
Period
‘AS can be seen from Table 2, milk activity decreases with a halflife of about one day until some time has elapsed (probably about four
or five days). The decay scheme then becomes a good deal more com-
plex and may vary widely among individual cows.
Milk to Grass Ratio
One of the objectives of the CERT project is to determine a ratio
of consumed activity in terms of curies per gram of ingested forage
to the resultant milk activity in terms of curies per liter of milk.
If a meaningful comparison is to be reached, the half-life or turnover
time in the cow as well as the sampling time increments must be
considered.