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Transfer Coefficients of Fallout Cesium-137 to Milk of Dairy Cattle Fed Pasture, Green-Cut Alfalfa, or Stored Feed1,2
Transfer Coefficients of Fallout Cesium-137 to Milk of Dairy Cattle Fed Pasture, Green-Cut Alfalfa, or Stored Feed :'" GERALD M. WARD, J. E. JOHNSON, and L. It. SASSER Department of Animal Science. Colorado State University, Fort Collins
cause of variable rates of contamination from the tr~>posphere, variable decay rates in the forage plants, and variation in daily intake by cows (11). In addition to the variability associated with this feeding system, forage consumption by cows on pasture cannot be measured with precision. As a result of rapid fluctuations in milk levels under pasture feeding, it is diffie:fit to provide estimates of the parameters controlling the transfer of fallout "~:Cs from the atmosphere to milk (1, 2). Studies by Kahn vt al. (8) report a transfer coefficient for ~/alhmt :~:Cs from t'eed to milk under pasture em~ditions of 0.68. Other research workers have studied the transfer, using tracer doses of ....Cs or '~Cs, and found values in excess of 1.0% (3, 4). A few values have been reported from this laboratory (10) indicating that the transfer coeflit.h,nt was related to the fiher content of the ratim:. This paper presents transfer coefficients of '~'Cs under pastm'e eonditions over a 3-yr period and values obtained under more closely controlled conditions by daily cutting of forage, as well as coefficients obtained under dry-lot feedinG' conditions.
Abstract
The transfer coefficient (per cent intake per liter of milk) of fallout ~'~:Cs was measured in the University herd under three feeding conditions. Groups of about ten Holstein cows were pastured for three summers and reeeived supplemental alfalfa hay and grain. The entire University herd of about 100 cows of four breeds was studied during the winter feeding period, when they received alfalfa hay, corn silage, and a grain mix. Eight Holsteins were fed alfalfu cut daily, together with small amounts of hay and grain according to production. All ~3:Cs demonstrations were made by gamma-ray spectrometry. The transfer coefficient was found to average 0.35 under pasture feedinG' conditions during the summers of 1962, 1963, and 1964. A mean of 0.41 was found during the winter feeding period of 1963, and a value of 0.25 when green-cut alfalfa was fed in the summer of 1965. The range in values was lowest for the dry-lot trial in which no breed effect was evident. Within treatments the level of crude tiber intake was not related to transfer coefficient.
Experimental Procedures
Contamination of cow's n:ilk with 'a:Cs is assoeiated with the contemporary fallout rate of this radionuelide, since soil uptake is negligible (6). To evaluate the hazards to man from environmental contamination, quantitative h> formation is necessary on the passage of this radionuclide into milk. The nmst direct route between falh)ut and milk is found where cows reeeive their sole feed supply from pasture. This feeding system also would be expected to produce the greatest variability in :*;Cs concentration of milk, beReeeived for publieation February 4, 1967. : Published with the approval of the Director of the Colorado Agricultural Experhnent Station as Scientific Series paper no. 1176. 2 This study was supported bv contract AT (11-1)1171 with the If. S. Atomic Energy Commission and published a,s paper no. COO-1171-54.
It: all eases the transfer coefficients are based on the total daily ':':('s intake, including supplemental feeds. The pasture management and sampling methods used to obtain the data from which transfer coefficients were calculated for milk from cows on p~stnre have been deserihed previously (14). The :~:Cs and potassimu intakes of cows in tile dry lot were estimated frmn analyses of feed samples obtained for two days before each milk sampli1:g period. Milk from eaeh group of cows was san:pied on nine occasions between January 17 and F e b r n a w 10, 1963, and the results averaged (Table 1). Feed consisted of alfalfa hay, corn silage, and emnmereial :nixed grain. H a y was sampled from each corral by collecting random samples from bales as they were fed. Silage was sampled front the feeder wagon at the time of feeding and grain was sampled regularly as new lots were delivered to the farm by bulk truck. Milk samples were
1092
1093
CESIUM T R A N S F E R TO F O R A G E
TABLE ] Fallout ~ C s concentrations in milk from eight lots of dairy cattle fed similar rations during the winter of 1963
Breed Holstein Holstein Holstein Brown Swiss Brown SMss Guernsey Jersey Mixed Mean
Milk produe('rude tion fiber (liters/ intake No. of cow(kg/ cows day) day) 13 8 20 8 11 15 13 15
18.8 21.0 16.5 14.2 19.0 12.7 13.8 25.8
4.0 4.4 3.7 4.0 4.4 3.5 3.5 4.1
Transfer coefficient 0.36 0.36 0.42 0.48 0.40 0.45 0.51 0.38
± .05 '~ ± .01 ± .03 -4- .02 +_ .02 ± .01 ± .03 +_ .07
0.41
" Mean and standard deviation of the mean. collected at the m o r n i n g milking from each cow a n d the milk pooled by corrals. The g r e e n - c u t a l f a l f a trial was conducted in 1965 with eight Holstein cows whose average milk p r o d u c t i o n was 23 kg p e r day at the beg i n n i n g a n d declined to a b o u t 19 kg p e r day a t the end of the trial. A l f a l f a was h a r v e s t e d f r o m a four-year-old s t a n d once a day with a f o r a g e c h o p p e r a n d blown into a truck. The surface area hmwested was calculated by meas u r i n g the l i n e a r distance traveled each (lay and m u l t i p l y i n g this by the width of the c u t t e r b a r (1.83 m ) . The area harvested p e r day r a n g e d f r o m 100 to 200 ~1~. The a m o u n t h a r vested was determined by weighing on a truck scale. A sample of a b o u t 5 kg was obtained f r o m the t r u c k a n d f r o m this sample a subs a m p l e o f a b o u t 400 g was selected a n d dried a t 45 C to obtain a dr?- m a t t e r percentage. The l a r g e r sample was dried at the same t e m p e r a t u r e a n d p r o v i d e d a sample f o r ~:Cs a n d ~°K determinations. A l t h o u g h h a r v e s t e d only once a day, the f o r a g e was offered to the cows twice a day. at 9 ~ a n d 5 P-'~. Cows were fed weighed a m o u n t s in i n d i v i d u a l stalls a n d an?' feed n o t eaten was weighed a n d sampled f o r d r y m a t t e r a n d ~:~:Cs determinations. S u p p l e m e n t a l a l f a l f a h a y was fed in the stalls in a m o u n t s va13"ing f r o m 2 to 6 kg p e r day, d e p e n d i n g u p o n the quality of p a s t u r e . The cows were milked twice a day, a t which time they received an a m o u n t of g r a i n mix p r o p o r t i o n a l to milk production. A composite milk sample was obtained each m o r n i n g f o r ~a:Cs analysis. The ~ C s c o n t e n t of g r a b b hay, corn silage, a n d green-cut alfalfa, as well as milk samples, was d e t e r m i n e d b y methods as described previ-
ously (13). F i b e r was d e t e r m i n e d by the acid d e t e r g e n t method of V a n Soest (12). Results and Discussion
The passage of f a l l o u t ~;Cs f r o m feed to milk was evaluated in t e r m s of the t r a n s f e r coefficient, defined as the p e r c e n t a g e of daily dietary "~Cs f o u n d p e r liter of milk. S t e w a r t (9) showed t h a t this method of calculation was more a p p r o p r i a t e in showing differences between cows t h a n a calculation based on total daily output. T r a n s f e r coefficients u n d e r p a s t u r e conditions were calculated each day f o r which data were available on b o t h p a s t u r e c o n c e n t r a t i o n s a n d milk levels of' ~:~:Cs, a n d a v e r a g e d a b o u t 12 values p e r month. D a y - t o - d a y v a r i a t i o n in the t r a n s f e r coefficients r a n g e d f r o m 0.15 to 1.0, b u t when ttle values were a v e r a g e d by months, the r a n g e was reduced to a b o u t 0.2 to 0.4 ( T a b l e 2). As TABLE Mean
transfer
2
coefficients of pasture
Month
1962
May June July August September
0.32 _ 0.17" 0.28 ± 0.10 0.44 ± 0.27 0.45 ± 0.14 ............
~3:Cs f o r
1963 0.22 0.38 0.30 0.36 0.41
± ± ± ~ ±
0.09 0.05 0.04 0.08 0.18
cows
on
1964 0.30 ~ 0.09 0.34 ± 0.15 0.18 ± 0.04
" Me~m ;n~d standard deviation of the mean. indicated by the s t a n d a r d deviations in Table 2, the v a r i a b i l i t y was g r e a t e r in 1962 t h a n in subsequent years, p r o b a b l y owing to improvem e n t s in s a m p l i n g techniques a n d to i m p r o v e d estimates of f o r a g e consumption. The m e a n t r a n s f e r coeffÉcient f o r all observations u n d e r p a s t u r e conditions was 0.35. The t r a n s f e r coefficient of 0.35 is significantly lower t h a n the value of 0.68 f o u n d by K a h n et al. (8) u n d e r p a s t m ' e conditions in Oregon. No seasonal p a t t e r n is a p p a r e n t in the data f r o m Table 2, n o r is there indication of significant v a r i a b i l i t y between years. The t r a n s f e r coefficient u n d e r dry-lot conditions was evaluated dm'ing the w i n t e r feeding p e r i o d in 1963. D a t a p r e s e n t e d in Table 1 r e p r e s e n t the a v e r a g e t r a n s f e r coefficient f o r eight g r o u p s of cows, fed in s e p a r a t e corrals and housed in open sheds. All the cows were fed similarly; however, the r a t i o of h a y to g r a i n varied a n d Table 1 r e p r e s e n t s the average daily crude fiber intake. The two highest t r a n s f e r coefficients were associated with the lowest crude fiber intakes which were f o u n d f o r the g r o u p s c o n t a i n i n g Guernsey a n d J e r s e y cows. However, in general, t r a n s f e r coefficients could J. DAIRY SCIE~'CE VOL. 50, NO. 7
1094
WARD, JOHNSON.
and sampling of feed could be rigorously controlled. The daily *~;Cs content of green-cut alfalfa is indicated in Fig. 1, on the basis of activity per kilogram of dry matter. The activity per cent of dry weight remained essentially the same until Day 200, when the decline coincided with the start of the second cutting. The daily output of ':':Cs per liter of milk is plotted in the lower part of Fig. 1, and is closely related to the activity of the alfalfa. Transfer coefficim~ts for this experiment are presented by weekly averages (Table 3). The variation in the transfer coefficients within weeks was considerable, ranging between 0.15 and 0.55. The rather large day-to-day variations arc not easy to explain, because the coefficient
not be related either to the small differences in fiber intake or to the breed of cow. I n this trial essentially the same feed had been fed for 150 days. The unweighted mean transfer coefficient of 0.41 is n o t significantly higher than the mean value of 0.35 (Table 1) for all pasture determinations. Both values are intermediate between the values of 0.24 and 0.58 obtained by Johnson (7), when rations were fed consisting principally of hay or principally of grain. Kahn et al. (8) found values of 0.68 and 0.80 under similar conditions of dry-lot feeding. During the summer of 1965, pasture studies were terminated and attention was given solely to forage-milk relationships under conditions of feeding daily harvested alfalfa where intake
GREEN - C U T
ALFALFA
ANI) S A S s E R
FEEDING
TRIAL
1965
io 4 .
Green
Cut
pCi/kg
Cs 13T ......
Milk
pCi/I
io 3
•
io 2
-
~
-/~ i x', "
"
--.
,'~
"
,,
"v"v d l l
-
~L,"
_
! ilia t! v
'
'r%.
V I,\A I
-
io I I
140
150
|
160
i
170
t
I
180
TIME
190
IN
I
!i
'
Ij
~/'.t/ t:~
i
I
t
200
210
220
L &
?30
I
i
240
250
DAYS
:FIG. 1. Comparison of la;Cs in green
¢ESIUS[
TRANSFER
TABLE 3 Transfer coefficients for nfilk and fiber content of green-cut alfalfa harvested iu the summer of 1965 and fed to Holstein cows Cutting date
Transfer coefficient
5/27-6/2 6/3 -6/9 6/10-6/16 6/17-6/23 6~24-6/30 7/1 -7/7 7/8 -7/14 7/15-7/21 7/22-7/28 7/29-8/4: 8/5 -8/11 8/12-8./16
.92 .36 .20 .29 .24 .20 .24 .20 .32 20 .23 .22
Mean
.25
_+ .09 ~ +_ .19 _+ .02 _+ .12 + .10 --+ .04 ± .12 ~ .07 _+ .16 ± .14 _+ .10 +-- .69
Acid detergent fiber ( ',,~) 26.5 3~.1 43.3 36.4 4].1 39.4 4(L8 45.1 38.(; 35.2 46.2
37.9
~' Mean and standard deviation of the mean. of v a r i a t i o n f o r s a m p l i n g a l f a l f a h a y u n d e r o u r conditions was only a b o u t 10~7} (13). The weekly means suggest, as did the p a s t u r e data, t h a t there was no seasonal p a t t e r n to the t r a n s f e r coefficient. The crude fiber content of the f o r a g e increased d u r i n g the g r o w i n g season, f r o m a n a v e r a g e of 26.5 in the first week of feeding to a h i g h of 45.1%. t t o w e v e r , there was no a p p a r e n t relation of the fiber content to the t r a n s f e r coefficient, as would be suggested by the data of S t e w a r t (9). The m e a n t r a n s f e r coefficient f o r the greenchop feeding season was 0.25, identical to the value obtained by J o h n s o n in a metabolic trial with d a i r y cows receiving a h i g h - h a y ration. The g r e e n - c u t f o r a g e was essentially all a l f a l f a a n d was h a r v e s t e d f r o m the same field as the b a y used by J o h n s o n (7) for his feeding trials. On the other h a n d , the t r a n s f e r coefficients for p a s t u r e feeding were similar to dtT-lot feeding conditions where the f o r a g e consisted of a l f a l f a h a y a n d corn silage. No good e x p l a n a t i o n is available f o r the similarities of these two feeding systems. The m e a n t r a n s f e r coefficients f o r the three feeding methods : 0.35 f o r p a s t u r e , 0.41 f o r drylot feeding, a n d 0.25 f o r green-cut a l f a l f a are n o t significantly different, because of the large s t a n d a r d deviation associated with green-cut alf a l f a feeding ( T a b l e 3). S a m p l e calibrations f o r milk a n d feed samples were based on the same primary, s t a n d a r d a n d all c o u n t i n g was perf o r m e d with the same equipment. Thus, differences in c o u n t i n g e r r o r s should not be a factor. However, t h e r e would a p p e a r to be real differenees between these values a n d the value of a b o u t 0.7 f o u n d b y K a h n et al. (8) f o r cows fed
TO F O R A G E
1095
in a similar m a n n e r in Oregon. Values are also lower by a f a c t o r of three t h a n those f o u n d in studies with t r a c e r doses of radiocesium (3-5). J o h n s o n (7) has f o u n d a t r a n s f e r e o e ~ c i e n t o f 0.96 when ~ C s was a d m i n i s t e r e d to cows fed a high r o u g h a g e ration, a n d a value of 1.36 f o r a low forage diet u n d e r conditions similar to those f o r the dry-lot experiment. A n y evaluation of the h a z a r d s to m a n of fallout ~:~Cs requires a n estimate f o r its passage t h r o u g h the milk-food chain. I t is o u r belief t h a t results f r o m daily h a r v e s t e d f o r a g e are more conclusive t h a n could be obtained f r o m p a s t u r e , despite the v a r i a b i l i t y in t r a n s f e r coefficients we encountered. The i n h e r e n t uncertainties in s a m p l i n g p a s t u r e f o r a g e a n d estim a t i n g intake are of such m a g n i t u d e t h a t no precise model of milk c o n t a m i n a t i o n can be produced with the data. The results can be a p p l i e d to p a s t u r e feeding situations with more confidence t h a n use of actual p a s t u r e data. I n addition, daily green feeding of f o r a g e is a n imp o r t a n t means of feeding dai13" cattle in the U n i t e d States, whereas p a s t u r e use is declining. References
(1 I Anderson, E. C., Ward, G. M., Holland, J. Z., and Langham, W. tI. 1962. Cesium-137 Levels in United States Powdered Milk and in the Population. TID Rcpt. no. 7632. pp. 477-516. Atomic Energy Commission, Oak Ridge, Tenn. (2) Anderson, W., Burton, L. K., and Crookall, J. C. 1961. Analysis of the Relationship Between Deposition of Long-Lived Fission Products and Level of Activity in Milk. Nature, 192: 1009. (3) Cr:~gle, R. G. 1961. Uptake and Excretion of Cesium-134 and Potassium-42 in Lactating Dairy Cows. J. Dairy Sci., 44: 352. (4) Garner, R. J. 1963. Environmental Contamination and Grazing Aniraals. Health Phys., 9: 507. (5) Hoe)d, S. L., and Comar, C. L. 1953. Metabolism of Cesium-137 in Rats and Farm Animals. Arch. Biochem. Biophys., 45: 423. (6) Johnson, J. E., Wilson, D. W., and Lindsay, W. L. 1966. Transfer of Eallout Cs t~7 from Soil to Dairy Cattle Feeds. Soil Sci. Soc. Am. Prec., 30: 416. (7) Johnson, James E. 1966. Metabolism of Fallout Cesium-137 in Bovine. Ph.D. thesis, p. 130. Colorado State University, Fort Collins. (8) Kqhn, B., Jones, I. R., Carter, M. W., Robbins, P. J., m~d Straub, C. P. 1965. Relation Between Amount of Cesium-137 in Cows" Feed and M i l k . . [ . Dairy Sei., 48:556. (9) Stewart, H. F. 1964. Factors h~fluencing the Levels of Cesimn-137 Secreted in Milk. J. DAIRY SCIENCE ~OL. 50, NO. 7
1096
WARD, JOHNSON. AND SASSER
p. 124. Ph.D. thesis, Colorado State University, F o r t Collins. (10) Stewart, H. F., Ward, G. M., and Johnson, J. E. 1965. Availability of Fallout Cs~7 to Dairy Cattle from Different Types of Feed. J. Dairy Sci., 48: 709. (11) U. S. Federal Radiation Council. 1965. Estimates of the Concentrations of Strontium89, Strontium-90 and Cesium-137 in Milk as a Function of Time After an Acute Localized Contaminating Event. Radiol. Health Data, 6: 383. (12) Van Soest, P. J. 1963. Use of Detergents in
J. DAIRY SCIENCE VOL. 50, NO. 7
the Analysis of Fibrous Feeds. II. A Rapid Method for the Determination of Fil)cr and Lignin. JAOAC, 46: 829. (13) Ward, G. M., Johnson, J. E., and Wilson, l). W. 1965. Determination of Fallout Radionuclides in El~vironmental Samples by Gannna-ray Spectrometry. Proe. Inter. Sympos. Radioisotopes Measurement Techniques in Medicine and Biology, p. 33, I A E A , Vienna. (14) W:~rd, G. M., Stewart, H. F., and Johnson, J.E. 1965. Effects of Feeding Practices on Cs1:~: Levels of Milk. J. Dairy Sci., 48 : 38.
cause of variable rates of contamination from the tr~>posphere, variable decay rates in the forage plants, and variation in daily intake by cows (11). In addition to the variability associated with this feeding system, forage consumption by cows on pasture cannot be measured with precision. As a result of rapid fluctuations in milk levels under pasture feeding, it is diffie:fit to provide estimates of the parameters controlling the transfer of fallout "~:Cs from the atmosphere to milk (1, 2). Studies by Kahn vt al. (8) report a transfer coefficient for ~/alhmt :~:Cs from t'eed to milk under pasture em~ditions of 0.68. Other research workers have studied the transfer, using tracer doses of ....Cs or '~Cs, and found values in excess of 1.0% (3, 4). A few values have been reported from this laboratory (10) indicating that the transfer coeflit.h,nt was related to the fiher content of the ratim:. This paper presents transfer coefficients of '~'Cs under pastm'e eonditions over a 3-yr period and values obtained under more closely controlled conditions by daily cutting of forage, as well as coefficients obtained under dry-lot feedinG' conditions.
Abstract
The transfer coefficient (per cent intake per liter of milk) of fallout ~'~:Cs was measured in the University herd under three feeding conditions. Groups of about ten Holstein cows were pastured for three summers and reeeived supplemental alfalfa hay and grain. The entire University herd of about 100 cows of four breeds was studied during the winter feeding period, when they received alfalfa hay, corn silage, and a grain mix. Eight Holsteins were fed alfalfu cut daily, together with small amounts of hay and grain according to production. All ~3:Cs demonstrations were made by gamma-ray spectrometry. The transfer coefficient was found to average 0.35 under pasture feedinG' conditions during the summers of 1962, 1963, and 1964. A mean of 0.41 was found during the winter feeding period of 1963, and a value of 0.25 when green-cut alfalfa was fed in the summer of 1965. The range in values was lowest for the dry-lot trial in which no breed effect was evident. Within treatments the level of crude tiber intake was not related to transfer coefficient.
Experimental Procedures
Contamination of cow's n:ilk with 'a:Cs is assoeiated with the contemporary fallout rate of this radionuelide, since soil uptake is negligible (6). To evaluate the hazards to man from environmental contamination, quantitative h> formation is necessary on the passage of this radionuclide into milk. The nmst direct route between falh)ut and milk is found where cows reeeive their sole feed supply from pasture. This feeding system also would be expected to produce the greatest variability in :*;Cs concentration of milk, beReeeived for publieation February 4, 1967. : Published with the approval of the Director of the Colorado Agricultural Experhnent Station as Scientific Series paper no. 1176. 2 This study was supported bv contract AT (11-1)1171 with the If. S. Atomic Energy Commission and published a,s paper no. COO-1171-54.
It: all eases the transfer coefficients are based on the total daily ':':('s intake, including supplemental feeds. The pasture management and sampling methods used to obtain the data from which transfer coefficients were calculated for milk from cows on p~stnre have been deserihed previously (14). The :~:Cs and potassimu intakes of cows in tile dry lot were estimated frmn analyses of feed samples obtained for two days before each milk sampli1:g period. Milk from eaeh group of cows was san:pied on nine occasions between January 17 and F e b r n a w 10, 1963, and the results averaged (Table 1). Feed consisted of alfalfa hay, corn silage, and emnmereial :nixed grain. H a y was sampled from each corral by collecting random samples from bales as they were fed. Silage was sampled front the feeder wagon at the time of feeding and grain was sampled regularly as new lots were delivered to the farm by bulk truck. Milk samples were
1092
1093
CESIUM T R A N S F E R TO F O R A G E
TABLE ] Fallout ~ C s concentrations in milk from eight lots of dairy cattle fed similar rations during the winter of 1963
Breed Holstein Holstein Holstein Brown Swiss Brown SMss Guernsey Jersey Mixed Mean
Milk produe('rude tion fiber (liters/ intake No. of cow(kg/ cows day) day) 13 8 20 8 11 15 13 15
18.8 21.0 16.5 14.2 19.0 12.7 13.8 25.8
4.0 4.4 3.7 4.0 4.4 3.5 3.5 4.1
Transfer coefficient 0.36 0.36 0.42 0.48 0.40 0.45 0.51 0.38
± .05 '~ ± .01 ± .03 -4- .02 +_ .02 ± .01 ± .03 +_ .07
0.41
" Mean and standard deviation of the mean. collected at the m o r n i n g milking from each cow a n d the milk pooled by corrals. The g r e e n - c u t a l f a l f a trial was conducted in 1965 with eight Holstein cows whose average milk p r o d u c t i o n was 23 kg p e r day at the beg i n n i n g a n d declined to a b o u t 19 kg p e r day a t the end of the trial. A l f a l f a was h a r v e s t e d f r o m a four-year-old s t a n d once a day with a f o r a g e c h o p p e r a n d blown into a truck. The surface area hmwested was calculated by meas u r i n g the l i n e a r distance traveled each (lay and m u l t i p l y i n g this by the width of the c u t t e r b a r (1.83 m ) . The area harvested p e r day r a n g e d f r o m 100 to 200 ~1~. The a m o u n t h a r vested was determined by weighing on a truck scale. A sample of a b o u t 5 kg was obtained f r o m the t r u c k a n d f r o m this sample a subs a m p l e o f a b o u t 400 g was selected a n d dried a t 45 C to obtain a dr?- m a t t e r percentage. The l a r g e r sample was dried at the same t e m p e r a t u r e a n d p r o v i d e d a sample f o r ~:Cs a n d ~°K determinations. A l t h o u g h h a r v e s t e d only once a day, the f o r a g e was offered to the cows twice a day. at 9 ~ a n d 5 P-'~. Cows were fed weighed a m o u n t s in i n d i v i d u a l stalls a n d an?' feed n o t eaten was weighed a n d sampled f o r d r y m a t t e r a n d ~:~:Cs determinations. S u p p l e m e n t a l a l f a l f a h a y was fed in the stalls in a m o u n t s va13"ing f r o m 2 to 6 kg p e r day, d e p e n d i n g u p o n the quality of p a s t u r e . The cows were milked twice a day, a t which time they received an a m o u n t of g r a i n mix p r o p o r t i o n a l to milk production. A composite milk sample was obtained each m o r n i n g f o r ~a:Cs analysis. The ~ C s c o n t e n t of g r a b b hay, corn silage, a n d green-cut alfalfa, as well as milk samples, was d e t e r m i n e d b y methods as described previ-
ously (13). F i b e r was d e t e r m i n e d by the acid d e t e r g e n t method of V a n Soest (12). Results and Discussion
The passage of f a l l o u t ~;Cs f r o m feed to milk was evaluated in t e r m s of the t r a n s f e r coefficient, defined as the p e r c e n t a g e of daily dietary "~Cs f o u n d p e r liter of milk. S t e w a r t (9) showed t h a t this method of calculation was more a p p r o p r i a t e in showing differences between cows t h a n a calculation based on total daily output. T r a n s f e r coefficients u n d e r p a s t u r e conditions were calculated each day f o r which data were available on b o t h p a s t u r e c o n c e n t r a t i o n s a n d milk levels of' ~:~:Cs, a n d a v e r a g e d a b o u t 12 values p e r month. D a y - t o - d a y v a r i a t i o n in the t r a n s f e r coefficients r a n g e d f r o m 0.15 to 1.0, b u t when ttle values were a v e r a g e d by months, the r a n g e was reduced to a b o u t 0.2 to 0.4 ( T a b l e 2). As TABLE Mean
transfer
2
coefficients of pasture
Month
1962
May June July August September
0.32 _ 0.17" 0.28 ± 0.10 0.44 ± 0.27 0.45 ± 0.14 ............
~3:Cs f o r
1963 0.22 0.38 0.30 0.36 0.41
± ± ± ~ ±
0.09 0.05 0.04 0.08 0.18
cows
on
1964 0.30 ~ 0.09 0.34 ± 0.15 0.18 ± 0.04
" Me~m ;n~d standard deviation of the mean. indicated by the s t a n d a r d deviations in Table 2, the v a r i a b i l i t y was g r e a t e r in 1962 t h a n in subsequent years, p r o b a b l y owing to improvem e n t s in s a m p l i n g techniques a n d to i m p r o v e d estimates of f o r a g e consumption. The m e a n t r a n s f e r coeffÉcient f o r all observations u n d e r p a s t u r e conditions was 0.35. The t r a n s f e r coefficient of 0.35 is significantly lower t h a n the value of 0.68 f o u n d by K a h n et al. (8) u n d e r p a s t m ' e conditions in Oregon. No seasonal p a t t e r n is a p p a r e n t in the data f r o m Table 2, n o r is there indication of significant v a r i a b i l i t y between years. The t r a n s f e r coefficient u n d e r dry-lot conditions was evaluated dm'ing the w i n t e r feeding p e r i o d in 1963. D a t a p r e s e n t e d in Table 1 r e p r e s e n t the a v e r a g e t r a n s f e r coefficient f o r eight g r o u p s of cows, fed in s e p a r a t e corrals and housed in open sheds. All the cows were fed similarly; however, the r a t i o of h a y to g r a i n varied a n d Table 1 r e p r e s e n t s the average daily crude fiber intake. The two highest t r a n s f e r coefficients were associated with the lowest crude fiber intakes which were f o u n d f o r the g r o u p s c o n t a i n i n g Guernsey a n d J e r s e y cows. However, in general, t r a n s f e r coefficients could J. DAIRY SCIE~'CE VOL. 50, NO. 7
1094
WARD, JOHNSON.
and sampling of feed could be rigorously controlled. The daily *~;Cs content of green-cut alfalfa is indicated in Fig. 1, on the basis of activity per kilogram of dry matter. The activity per cent of dry weight remained essentially the same until Day 200, when the decline coincided with the start of the second cutting. The daily output of ':':Cs per liter of milk is plotted in the lower part of Fig. 1, and is closely related to the activity of the alfalfa. Transfer coefficim~ts for this experiment are presented by weekly averages (Table 3). The variation in the transfer coefficients within weeks was considerable, ranging between 0.15 and 0.55. The rather large day-to-day variations arc not easy to explain, because the coefficient
not be related either to the small differences in fiber intake or to the breed of cow. I n this trial essentially the same feed had been fed for 150 days. The unweighted mean transfer coefficient of 0.41 is n o t significantly higher than the mean value of 0.35 (Table 1) for all pasture determinations. Both values are intermediate between the values of 0.24 and 0.58 obtained by Johnson (7), when rations were fed consisting principally of hay or principally of grain. Kahn et al. (8) found values of 0.68 and 0.80 under similar conditions of dry-lot feeding. During the summer of 1965, pasture studies were terminated and attention was given solely to forage-milk relationships under conditions of feeding daily harvested alfalfa where intake
GREEN - C U T
ALFALFA
ANI) S A S s E R
FEEDING
TRIAL
1965
io 4 .
Green
Cut
pCi/kg
Cs 13T ......
Milk
pCi/I
io 3
•
io 2
-
~
-/~ i x', "
"
--.
,'~
"
,,
"v"v d l l
-
~L,"
_
! ilia t! v
'
'r%.
V I,\A I
-
io I I
140
150
|
160
i
170
t
I
180
TIME
190
IN
I
!i
'
Ij
~/'.t/ t:~
i
I
t
200
210
220
L &
?30
I
i
240
250
DAYS
:FIG. 1. Comparison of la;Cs in green
¢ESIUS[
TRANSFER
TABLE 3 Transfer coefficients for nfilk and fiber content of green-cut alfalfa harvested iu the summer of 1965 and fed to Holstein cows Cutting date
Transfer coefficient
5/27-6/2 6/3 -6/9 6/10-6/16 6/17-6/23 6~24-6/30 7/1 -7/7 7/8 -7/14 7/15-7/21 7/22-7/28 7/29-8/4: 8/5 -8/11 8/12-8./16
.92 .36 .20 .29 .24 .20 .24 .20 .32 20 .23 .22
Mean
.25
_+ .09 ~ +_ .19 _+ .02 _+ .12 + .10 --+ .04 ± .12 ~ .07 _+ .16 ± .14 _+ .10 +-- .69
Acid detergent fiber ( ',,~) 26.5 3~.1 43.3 36.4 4].1 39.4 4(L8 45.1 38.(; 35.2 46.2
37.9
~' Mean and standard deviation of the mean. of v a r i a t i o n f o r s a m p l i n g a l f a l f a h a y u n d e r o u r conditions was only a b o u t 10~7} (13). The weekly means suggest, as did the p a s t u r e data, t h a t there was no seasonal p a t t e r n to the t r a n s f e r coefficient. The crude fiber content of the f o r a g e increased d u r i n g the g r o w i n g season, f r o m a n a v e r a g e of 26.5 in the first week of feeding to a h i g h of 45.1%. t t o w e v e r , there was no a p p a r e n t relation of the fiber content to the t r a n s f e r coefficient, as would be suggested by the data of S t e w a r t (9). The m e a n t r a n s f e r coefficient f o r the greenchop feeding season was 0.25, identical to the value obtained by J o h n s o n in a metabolic trial with d a i r y cows receiving a h i g h - h a y ration. The g r e e n - c u t f o r a g e was essentially all a l f a l f a a n d was h a r v e s t e d f r o m the same field as the b a y used by J o h n s o n (7) for his feeding trials. On the other h a n d , the t r a n s f e r coefficients for p a s t u r e feeding were similar to dtT-lot feeding conditions where the f o r a g e consisted of a l f a l f a h a y a n d corn silage. No good e x p l a n a t i o n is available f o r the similarities of these two feeding systems. The m e a n t r a n s f e r coefficients f o r the three feeding methods : 0.35 f o r p a s t u r e , 0.41 f o r drylot feeding, a n d 0.25 f o r green-cut a l f a l f a are n o t significantly different, because of the large s t a n d a r d deviation associated with green-cut alf a l f a feeding ( T a b l e 3). S a m p l e calibrations f o r milk a n d feed samples were based on the same primary, s t a n d a r d a n d all c o u n t i n g was perf o r m e d with the same equipment. Thus, differences in c o u n t i n g e r r o r s should not be a factor. However, t h e r e would a p p e a r to be real differenees between these values a n d the value of a b o u t 0.7 f o u n d b y K a h n et al. (8) f o r cows fed
TO F O R A G E
1095
in a similar m a n n e r in Oregon. Values are also lower by a f a c t o r of three t h a n those f o u n d in studies with t r a c e r doses of radiocesium (3-5). J o h n s o n (7) has f o u n d a t r a n s f e r e o e ~ c i e n t o f 0.96 when ~ C s was a d m i n i s t e r e d to cows fed a high r o u g h a g e ration, a n d a value of 1.36 f o r a low forage diet u n d e r conditions similar to those f o r the dry-lot experiment. A n y evaluation of the h a z a r d s to m a n of fallout ~:~Cs requires a n estimate f o r its passage t h r o u g h the milk-food chain. I t is o u r belief t h a t results f r o m daily h a r v e s t e d f o r a g e are more conclusive t h a n could be obtained f r o m p a s t u r e , despite the v a r i a b i l i t y in t r a n s f e r coefficients we encountered. The i n h e r e n t uncertainties in s a m p l i n g p a s t u r e f o r a g e a n d estim a t i n g intake are of such m a g n i t u d e t h a t no precise model of milk c o n t a m i n a t i o n can be produced with the data. The results can be a p p l i e d to p a s t u r e feeding situations with more confidence t h a n use of actual p a s t u r e data. I n addition, daily green feeding of f o r a g e is a n imp o r t a n t means of feeding dai13" cattle in the U n i t e d States, whereas p a s t u r e use is declining. References
(1 I Anderson, E. C., Ward, G. M., Holland, J. Z., and Langham, W. tI. 1962. Cesium-137 Levels in United States Powdered Milk and in the Population. TID Rcpt. no. 7632. pp. 477-516. Atomic Energy Commission, Oak Ridge, Tenn. (2) Anderson, W., Burton, L. K., and Crookall, J. C. 1961. Analysis of the Relationship Between Deposition of Long-Lived Fission Products and Level of Activity in Milk. Nature, 192: 1009. (3) Cr:~gle, R. G. 1961. Uptake and Excretion of Cesium-134 and Potassium-42 in Lactating Dairy Cows. J. Dairy Sci., 44: 352. (4) Garner, R. J. 1963. Environmental Contamination and Grazing Aniraals. Health Phys., 9: 507. (5) Hoe)d, S. L., and Comar, C. L. 1953. Metabolism of Cesium-137 in Rats and Farm Animals. Arch. Biochem. Biophys., 45: 423. (6) Johnson, J. E., Wilson, D. W., and Lindsay, W. L. 1966. Transfer of Eallout Cs t~7 from Soil to Dairy Cattle Feeds. Soil Sci. Soc. Am. Prec., 30: 416. (7) Johnson, James E. 1966. Metabolism of Fallout Cesium-137 in Bovine. Ph.D. thesis, p. 130. Colorado State University, Fort Collins. (8) Kqhn, B., Jones, I. R., Carter, M. W., Robbins, P. J., m~d Straub, C. P. 1965. Relation Between Amount of Cesium-137 in Cows" Feed and M i l k . . [ . Dairy Sei., 48:556. (9) Stewart, H. F. 1964. Factors h~fluencing the Levels of Cesimn-137 Secreted in Milk. J. DAIRY SCIENCE ~OL. 50, NO. 7
1096
WARD, JOHNSON. AND SASSER
p. 124. Ph.D. thesis, Colorado State University, F o r t Collins. (10) Stewart, H. F., Ward, G. M., and Johnson, J. E. 1965. Availability of Fallout Cs~7 to Dairy Cattle from Different Types of Feed. J. Dairy Sci., 48: 709. (11) U. S. Federal Radiation Council. 1965. Estimates of the Concentrations of Strontium89, Strontium-90 and Cesium-137 in Milk as a Function of Time After an Acute Localized Contaminating Event. Radiol. Health Data, 6: 383. (12) Van Soest, P. J. 1963. Use of Detergents in
J. DAIRY SCIENCE VOL. 50, NO. 7
the Analysis of Fibrous Feeds. II. A Rapid Method for the Determination of Fil)cr and Lignin. JAOAC, 46: 829. (13) Ward, G. M., Johnson, J. E., and Wilson, l). W. 1965. Determination of Fallout Radionuclides in El~vironmental Samples by Gannna-ray Spectrometry. Proe. Inter. Sympos. Radioisotopes Measurement Techniques in Medicine and Biology, p. 33, I A E A , Vienna. (14) W:~rd, G. M., Stewart, H. F., and Johnson, J.E. 1965. Effects of Feeding Practices on Cs1:~: Levels of Milk. J. Dairy Sci., 48 : 38.