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Relative importance of ewe milk and pasture in transferring radiocaesium to lambs during the summer grazing period
Small Ruminant Research ELSEVIER
Small Ruminant Research 14 (1994) 199-204
Relative importance of ewe milk and pasture in transferring radiocaesium to lambs during the summer grazing period H.S. Hansen a'*, K. Hove a, K. Barvik b, A. V~benOb aDepartment of Animal Science, Agricultural, University of Norway, P.O. Box 5025, 1432/is, Norway bTjctta Research Station, 8860 Tjctta, Norway (Accepted 5 December 1993)
Abstract The relative importance of milk and pasture in transferring radiocaesium ( 134Cs and 137Cs) to lamb's meat was studied in 13 ewes with twin lambs grazing on pastures contaminated by deposition from the Chernobyl accident. Six of the ewes were fed a caesium binder to obtain low milk radiocaesium levels and seven were used as control. Radiocaesium activity concentration was measured in meat, blood and milk every 14 d. Milk was the major source of radiocaesium for lambs younger than 6-7 wk, but from 11 wk onwards milk had only a slight and non-significant effect on radiocaesium concentration in lamb's meat. Thus, radiocaesium intake from pasture was the major factor determining radiocaesium concentration in lambs at time of slaughter. Mean aggregated transfer coefficients to meat were 23 × 10- 3 m 2 k g - ~and 31 × 10- 3 m 2 k g - ~for ewes and lambs, respectively, and mean aggregated transfer coefficient to ewes milk was 11 × 10 3 m 21- ~. Keywords: Lamb; Milk; Pasture; Radiocaesium; Transfer coefficient
I. Introduction
In Norway, ewes and their lambs, born in April or May, are usually released on mountain pasture in late June. Some of the mountain areas heavily used for lamb production were contaminated by radiocaesium ( 134Cs and ~37Cs) fallout from the Chernobyl accident in 1986. Each year since 1986, between 10-30% of the lambs intended for slaughter had radiocaesium levels in meat above the intervention limit of 600 Bq k g - ~ . These animals were given uncontaminated feed for periods of 4 - 1 2 wk to reduce radiocaesium levels before slaughter. The farmers were economically compensated from *Corresponding author. 0921-4488/94/$07.00 © 1994 Elsevier Science B:V. All rights reserved SSD10921-4488(93) E 0 1 3 8 - I
the government for the increased expenses for feed and labour. During the pasture period lambs receive radiocaesium from both vegetation and milk. The proportion of energy intake from milk declines from a mean of 88% at 5 wk of age to 15-20% at 14 wk of age (Doney and Peart, 1976; G i b b e t al., 1981 ). The relative importance of milk and pasture in transferring radiocaesium to lambs depends not only on intake, but also on absorption of radiocaesium from the two sources. The absorption was found to be higher from milk than from grass in 16-wk-old lambs by Mayes et al. (1992). Therefore, milk could be more important in transferring radiocaesium to lambs than its proportion of the energy supply would predict. One possible way of reducing the radiocaesium levels in lambs meat could be to reduce the
200
H.S. Hansen et al. / Small Ruminant Re,~earch 14 (1994) 199-204
radiocaesium levels in ewes' milk by supplying caesium binders to ewes. To evaluate the importance of radiocaesium transfer to lambs via milk, an experiment was undertaken to determine the relative importance of radiocaesium from milk and pasture when both ewes and lambs grazed on contaminated pasture.
3000
Q
2500
2000
2. Materials and methods
g
Thirteen ewes of the Speel breed were used. The ewes were between 2 and 6 years old and all had twin lambs, 3 weeks of age at the start of the experiment. The ewes and their lambs were divided into a control group of seven ewes and a test group of six ewes. In the test group, low radiocaesium concentration in milk was maintained feeding 300 mg d ~ of the caesium binder ammonium-iron-hexacyanoferrate ( A F C F group) mixed in 100 g of dairy concentrate (Hove et al., 1992). After d 28 the A F C F was administered with sustained release boli, each bolus was 20 mm diameter, 67 mm long, weighed 50 g and released A F C F at a rate of about 50 mg d - ~ (Hove and Hansen, i 993). Two boli were given to each ewe every 14 d. The experiment was conducted at Tjotta Research Station, a coastal site (50 m above sea level) in northern Norway (66.6°N, 12.3°E). The animals were released on pasture A (0.8 ha) on 25 May 1988 (Fig. 1 ). After 28 days the animals were moved to pasture B (0.4 ha, Fig. 1 ), a peat soil type pasture where the mean radiocaesium deposition in 1988 was 44 kBq m 2 and the radiocaesium content of vegetation was higher than on pasture A (K. Hove, unpublished observations). The animals remained on pasture B for 56 d until 18 August. Milk samples were taken from all ewes every 14 d. Oxytocin (10 IU) was given subcutaneously to the ewes and a 20 ml sample was milked by hand 2 min later. Blood samples were taken from the jugular vein of all lambs and ewes at the same time. Plasma was separated and discarded after centrifugation and radiocaesium was measured in 5 ml of the red blood cell ( R B C ) suspension. Live monitoring measurements were performed to document radiocaesium levels in meat. All experimental animals were weighed on the days of sampling. Vegetation samples were obtained from six exclosure cages on pasture A, and from two grazed locations
g
1500
1000 m
~
5oo
0
14 28 Pasture A
42
56
70 84 Pasture 13
Time (d)
Fig. 1. Radiocaesium content in mixed species samples from pasture A (from d 0 to d 28 of the experiment) and pasture B (from d 28 to d 84 of the experiment).
on pasture B. Mixed species samples were taken every 14 d, dried at 65°C for 2 days and ground to pass through a 1 mm sieve. Aliquots of 4 - 8 g were analysed for radiocaesium content. Radiocaesium in milk, blood and vegetation was measured by gamma-spectrometry, using a NaI(TI) scintillation detector (Packard Minaxi auto gamma5000 series). Blood samples were counted for 50 min and milk and vegetation for 30 min. The measurements were made by the Isotope Laboratory at The Agricultural University of Norway. A portable counter (Canberra Series 10 plus with a 7.5 cm N a I ( T I ) scintillator) was used for the live monitoring measurements (Strand and Brynhildsen, 1990). Aggregated transfer coefficient for radiocaesium to meat and milk was estimated as the ratio Bq k g - ~ meat or milk/deposition Bq m 2. The transfer coefficients from vegetation to meat ( F r v a l u e s ) were estimated as Bq k g - i m e a t / B q d - J ( W a r d and Johnson, 1986). Differences in radiocaesium activity concentrations between the two groups were compared using one way analysis of variance (SAS, 1990).
H.S. Hansen et al. / Small Ruminant Research 14 (1994) 199-204
3. Results
Vegetation The radiocaesium content of mixed species samples were 4 2 0 + 160 Bq kg-~ DM on pasture A and 2730+340 Bq k g - ' DM on pasture B (Fig. 1). No significant changes in radiocaesium levels were observed with time during the periods when the two pastures were used.
Ewes Radiocaesium levels in milk were 6-times higher when ewes were grazing pasture B than pasture A, equivalent to the magnitude of difference in radiocaesium levels in the two pastures. Mean milk radiocaesium levels in the control and AFCF group were stable after 14 d on pasture B (control group 4 6 0 + 124 Bq 1-' and AFCF group 110+65 Bq l -l, P < 0 . 0 5 , Fig. 2). The mean aggregated transfer coefficient to milk in control group was 11 x 10 - 3 m 2 ! -~. Meat radiocaesium levels measured by live monitoring showed the same pattern with stable values for ewes in the two groups 28 d after moving to pasture B. Mean radiocaesium concentration in the control group levelled out at 1000 Bq k g - ' . The AFCF group had throughout the experiment a stable mean radiocaesium
201
concentration which was 70% lower than the control group (P < 0.05, Fig. 3). The mean aggregated transfer coefficient to meat in the control group was 23 × 10-3 m2 k g - ' Radiocaesium levels in RBC were below the limit of detection until d 42. The level in the control ewes increased from d 42 to d 56 and plateaued at 99 + 62 Bq 1- '. Ewes in the AFCF group had mean RBC radiocaesium levels 75% lower ( 2 5 + 2 0 Bq 1-1, Fig. 4). Due to large variation between animals this difference was significant only at d 70. Ewes in the control group weighed 70.2 + 9.6 kg at the start of the experiment and 68.0+ 10.2 kg at the end. Ewes in the AFCF group weighed 69.7 + 9.5 kg at the start and 65.3 -t- 10.2 kg at the end of the experiment. Lambs Radiocaesium content in lamb's meat was 6-7-times higher after 28 d of grazing pasture B compared to pasture A. On d 28 of the experiment the control lambs had lower mean radiocaesium concentration in meat than the AFCF lambs (P<0.05, Fig. 3). After 4 wk on pasture B the lambs in the control group had mean radiocaesium concentrations of 1300-1500 Bq kg-~. 2000 o • [] •
800 o Control • AFCF group
700
Control e w e s Ewes fed AFCF Control lambs Lambs of e w e s fed AFCF
1500 6OO
~oo =_
£
~,
E .c_
300
o
1000
4O0
o
500
r.,,200
cl~ IO0 0 0
I
I
I
10
20
30
I
I
40 50 Time (d)
I
I
I
60
70
80
0 90
Fig. 2. Radiocaesium concentration in milk from ewes grazing on contaminated pasture A and pasture B as in Fig. 1. Mean and SD of six ewes fed caesium binder ( A F C F group) and seven control ewes.
10
20
30
40 50 Time (d)
60
70
80
90
Fig. 3. Radiocaesium concentration in meat measured by live monitoring. The animals were grazing on contaminated pasture A and pasture B as in Fig. 1. Mean and SD of six ewes fed caesium binder ( A F C F group), their twin lambs and seven control ewes with their twin lambs.
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H.S. Hansen et a l . / Small Ruminant Research 14 (1994) 199-204
OControl e w e s e E w e s fed AFCF [] Control Iambs mLambs of ewes fed AFCF
200
150 ,-t"
"i
1 O0
o rr
50
0 40
I
I
I
I
50
60
70
80
90
Time (dl
Fig. 4. Radiocaesium concentration in red blood cells (RBC) in ewes and lambs grazing pasture B. Mean of six ewes fed caesium binder (AFCF group) and their twin lambs, and seven control ewes and their twin lambs.
Lambs in the AFCF group did not differ significantly from the control lambs when grazing pasture B (Fig. 3). Lambs accumulated about 25% more radiocaesium per kg BW than the control ewes did. The aggregated transfer coefficient for lambs was 31 × 10 -3 m 2 k g - ~. The Ff-value on d 84 for lambs from both groups was estimated at 1.0 d kg ~ based on consumption of 0.5 kg DM pasture and negligible amounts of milk (Table 1). Measurements of radiocaesium in RBC in lambs were below the limit of detection until d 42. These RBC values increased from 70-80 Bq 1- ~measured on d 42 to 120-140 Bq 1- ' from d 56 and through the end of the experiment ( P > 0.05, Fig. 4), Lambs in the control group increased BW from 12.6 + 2.1 kg to 29.5 _ 4.5 kg and the AFCF group from 13.0___ 1.5 kg to 28.8___4.8 kg from start to end of the experiment. This equalled a growth rate of 190 g d and 200 g d ' for the control and AFCF group, respectively.
4. Discussion The accumulation of radiocaesium in lambs is determined by the total intake of contaminated feed and the
absorption of the ingested radiocaesium. In 7-wk-old lambs the radiocaesium intake from milk was estimated to be 38% of the total intake in control lambs, and 12% in the AFCF Iambs (Table 1). Meat radiocaesium levels were also significantly different between the two groups at 7 wk of age. This showed that milk derived radiocaesium was the major source of radiocaesium accumulation in young lambs up to 7 wk of age. When grazing pasture B the milk derived radiocaesium intake was estimated to decrease from 27% to 13% in the control lambs and from 7% to 3% in the AFCF lambs from d 42 to d 70 in the experiment. In these calculations similar feed energy intakes between the two groups were assumed, because all lambs grazed the same pasture and had about the same mean growth rates. Somewhat higher absorption of radiocaesium from milk than from vegetation has been reported in lambs ( 100% vs. 85%, Mayes et al., 1992). The reduction in milk intake as the lambs mature implicated nevertheless that radiocaesium from vegetation is the main source of absorbed caesium. As a consequence the use of AFCF which reduced the radiocaesium level in milk by 75% did not significantly affect the accumulation of radiocaesium in lambs older than 11 wk. Mean RBC radiocaesium levels showed the same relations between the two groups of lambs and the two groups of ewes as the results from milk and meat. However, the variation between animals was greater for the RBC measurements and significant difference was found only between the two groups of ewes for d 70. These findings are in agreement with results from a field study involving 130 lambs where no difference between lambs of ewes treated with caesium binders and lambs of untreated ewes were observed (H.S. Hansen, unpublished data). The 5-7-fold increase in radiocaesium accumulation in milk and meat (Figs. 2 and 3) after d 28 was likely to be a response to the 6-fold increase in raqliocaesium concentration in the vegetation from pasture A and pasture B. The aggregated transfer coefficient estimated for pasture B was found to be 25% higher for lambs than ewes, which was in agreement with results of Howard (1989) that lambs accumulate more radiocaesium per kg BW than ewes when grazing the same pasture. The Frvalue for lambs was estimated at 1.0 d k g - ', which is somewhat higher than most studies have found, but well within the range from 0.24 to 1.61 d kg '
H.S. Hansen et al. /Small Ruminant Research 14 (1994) 199-204
203
Table 1 Estimated daily radiocaesium intake from pasture and milk in lambs in the control and AFCF group Time of experiment (d )
Age of lambs ( wk )
Pasture
Milk intake" kgDMd
14 28 42 56 70
5 7 9 11 13
A A B B B
0.15 0.25 0.3 0.4 0.5
i
Bqd
i
63 105 810 1080 1350
intake ~
control
ld -~
Bqd
1.1 0.9 0.6 0.5 0.4
68 65 300 250 200
AFCF L
%oftotal
Bqd
52 38 27 19 13
17 15 60 50 40
~
%oftotal 21 12 7 4 3
Pasture A was used from d 0-28 and pasture B from d 28-84. alntake of pasture (kg DM d ~) and milk ( 1 d - ~) for lambs with a daily weight gain of 150-200 g d - ~ ( Gibbet al., 19891 ).
(Howard et al., 1987; Andersson and Hansson, 1989; Beresford et al., 1989; Howard et al., 1989) The time required to attain stable levels in radiocaesium concentration in milk ( 14 d), meat (28 d) and RBC (28 d) are generally in agreement with half-lives reported in the literature (Shannon et al., 1965; Assimakopoulos et al., 1987; Howard et al., 1987; Hove and Ekern, 1988; Martin et al., 1989).
5. Conclusion When ewes and lambs graze together on pastures contaminated with radiocaesium, milk was the major source for radiocaesium accumulation in lambs younger than 6-7 wk. However, when lambs were ready for slaughter at the age of 15-20 wk, pasture radiocaesium would almost exclusively determine meat radiocaesium levels. Caesium binders given to ewes will only affect the radiocaesium content of lambs when the lambs are young. 6. Acknowledgement The authors acknowledge the financial support for this study from the Norwegian Agricultural Research Council.
References Andersson, I. and Hansson, I., 1989. Distribution of ~37Csto different muscles and internal organs of lambs fed contaminated hay. Swedish J. Agric. Res., 19: 93-98.
Assimakopoulos, P.A., Ioannides, K.G., Pakou, A.A. and Mantzios, A., 1987. Measurement of the transfer coefficient for radiocaeslum transport from a sheep's diet to its milk. Health Phys., 53: 685-689. Beresford, N.A., Lamb, C.S., Mayes, R.W., Howard, B.J. and Colgrove, P.M., 1989. The effect of treating pasture with bentonite on the transfer of 137Csfrom grazed herbage to sheep. J. Environ. Radioactivity, 9:251-264. Doney, J.M. and Peart, J.N., 1976. The effect of sustained lactation on intake of solid food and growth rate of lambs, J. Agric. Sci. Camb., 87:511-518. Gibb, M.J., Treacher, T.T. and Shanmugalingam, V.S.. 1981. Herbage intake and performance of grazing ewes and of their lambs when weaned at 6, 8, 10 or 14 weeks of age. Anita. Prod., 33: 223-232. Hove, K. and Ekern, A., 1988. Combating radiocaesium contamination in farm animals. In: LSg, J. lEd.), Health Problems in Connection with Radiation from Radioactive Matter in Fertilizers, Soils and Rocks, Norwegian University Press, Oslo, pp. 139153. Hove. K., Staaland, H. and Pedersen, ~., 1992. Hexacyanoferrates and bentonite as binders of radiocaesium for reindeer. Rangifer, I 1: 43-48. Hove, K. and Hansen, H.S., 1993. Reduction of radiocaesium transfer to animal products using sustained release boll with ammoniumiron(Ill) -hexacyanoferrate(ll). Acta. Vet. Scand., 34: 287297. Howard, B.J., 1989. A comparison of radiocaesium transfer coefficients for sheep milk and muscle derived from both field and laboratory studies. Sci. Total Environ., 85: 189-198. Howard, BJ., Beresford, N.A., Burrow, L., Shaw, P.V. and Curtis, E.J.C., 1987. A comparison of caesium 137 and 134 activity in sheep remaining on upland areas contaminated by Chernobyl fallout with those removed to less active lowland pasture. J. Soc. Radiol. Prot., 7: 71-73. Howard, B.J., Mayes, R.W., Beresford, N.A. and Lamb, C.S., 1989. Transfer of radiocaesium from different environmental sources to ewes suckling lambs. Health Phys., 57: 579-586. Martin, C.J., Heaton, B and Thompson, J., 1989. Cesium-137, ~'4Cs and ~")mAg in lambs grazing pasture in NE Scotland contami-
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H.S. Hansen et al. / Small R m n i m m t Research 14 (1994) 199-204
nated by Chernobyl fallout. Health Phys., 56: 459-464. Mayes, R.W., Eayres, H.F., Beresford, N.A., Lamb, C.S. and Howard, B.J., 1992. Changes with age in the absorption of radiocaesium by sheep. Radiat. Prot. Dosim., 41: 83-86. Shannon, R.O.. McClellan, R.O., Watson. C.R. and Bustad, L.K., 1965. Public health aspects of caesium-137 in ruminants. J. Am. Vet. Med. Assoc., 147:1488-1491.
SAS, 1990. SAS User's Guide: Statistics version 6 edition. SAS Institute Inc., Cary, NC, USA, 1686 pp. Strand, P. and Brynhildsen, L., 1990. Rapid method for live monitoring of caesium activity in sheep, cattle and reindeer. International Atomic Energy Agency, Vienna IAEA-SM-306/37P 1, 485-486. Ward, G.M. and Johnson, J.E., 1986. Validity of the term transfer coefficient. Health Phys., 50:411-414.
Small Ruminant Research 14 (1994) 199-204
Relative importance of ewe milk and pasture in transferring radiocaesium to lambs during the summer grazing period H.S. Hansen a'*, K. Hove a, K. Barvik b, A. V~benOb aDepartment of Animal Science, Agricultural, University of Norway, P.O. Box 5025, 1432/is, Norway bTjctta Research Station, 8860 Tjctta, Norway (Accepted 5 December 1993)
Abstract The relative importance of milk and pasture in transferring radiocaesium ( 134Cs and 137Cs) to lamb's meat was studied in 13 ewes with twin lambs grazing on pastures contaminated by deposition from the Chernobyl accident. Six of the ewes were fed a caesium binder to obtain low milk radiocaesium levels and seven were used as control. Radiocaesium activity concentration was measured in meat, blood and milk every 14 d. Milk was the major source of radiocaesium for lambs younger than 6-7 wk, but from 11 wk onwards milk had only a slight and non-significant effect on radiocaesium concentration in lamb's meat. Thus, radiocaesium intake from pasture was the major factor determining radiocaesium concentration in lambs at time of slaughter. Mean aggregated transfer coefficients to meat were 23 × 10- 3 m 2 k g - ~and 31 × 10- 3 m 2 k g - ~for ewes and lambs, respectively, and mean aggregated transfer coefficient to ewes milk was 11 × 10 3 m 21- ~. Keywords: Lamb; Milk; Pasture; Radiocaesium; Transfer coefficient
I. Introduction
In Norway, ewes and their lambs, born in April or May, are usually released on mountain pasture in late June. Some of the mountain areas heavily used for lamb production were contaminated by radiocaesium ( 134Cs and ~37Cs) fallout from the Chernobyl accident in 1986. Each year since 1986, between 10-30% of the lambs intended for slaughter had radiocaesium levels in meat above the intervention limit of 600 Bq k g - ~ . These animals were given uncontaminated feed for periods of 4 - 1 2 wk to reduce radiocaesium levels before slaughter. The farmers were economically compensated from *Corresponding author. 0921-4488/94/$07.00 © 1994 Elsevier Science B:V. All rights reserved SSD10921-4488(93) E 0 1 3 8 - I
the government for the increased expenses for feed and labour. During the pasture period lambs receive radiocaesium from both vegetation and milk. The proportion of energy intake from milk declines from a mean of 88% at 5 wk of age to 15-20% at 14 wk of age (Doney and Peart, 1976; G i b b e t al., 1981 ). The relative importance of milk and pasture in transferring radiocaesium to lambs depends not only on intake, but also on absorption of radiocaesium from the two sources. The absorption was found to be higher from milk than from grass in 16-wk-old lambs by Mayes et al. (1992). Therefore, milk could be more important in transferring radiocaesium to lambs than its proportion of the energy supply would predict. One possible way of reducing the radiocaesium levels in lambs meat could be to reduce the
200
H.S. Hansen et al. / Small Ruminant Re,~earch 14 (1994) 199-204
radiocaesium levels in ewes' milk by supplying caesium binders to ewes. To evaluate the importance of radiocaesium transfer to lambs via milk, an experiment was undertaken to determine the relative importance of radiocaesium from milk and pasture when both ewes and lambs grazed on contaminated pasture.
3000
Q
2500
2000
2. Materials and methods
g
Thirteen ewes of the Speel breed were used. The ewes were between 2 and 6 years old and all had twin lambs, 3 weeks of age at the start of the experiment. The ewes and their lambs were divided into a control group of seven ewes and a test group of six ewes. In the test group, low radiocaesium concentration in milk was maintained feeding 300 mg d ~ of the caesium binder ammonium-iron-hexacyanoferrate ( A F C F group) mixed in 100 g of dairy concentrate (Hove et al., 1992). After d 28 the A F C F was administered with sustained release boli, each bolus was 20 mm diameter, 67 mm long, weighed 50 g and released A F C F at a rate of about 50 mg d - ~ (Hove and Hansen, i 993). Two boli were given to each ewe every 14 d. The experiment was conducted at Tjotta Research Station, a coastal site (50 m above sea level) in northern Norway (66.6°N, 12.3°E). The animals were released on pasture A (0.8 ha) on 25 May 1988 (Fig. 1 ). After 28 days the animals were moved to pasture B (0.4 ha, Fig. 1 ), a peat soil type pasture where the mean radiocaesium deposition in 1988 was 44 kBq m 2 and the radiocaesium content of vegetation was higher than on pasture A (K. Hove, unpublished observations). The animals remained on pasture B for 56 d until 18 August. Milk samples were taken from all ewes every 14 d. Oxytocin (10 IU) was given subcutaneously to the ewes and a 20 ml sample was milked by hand 2 min later. Blood samples were taken from the jugular vein of all lambs and ewes at the same time. Plasma was separated and discarded after centrifugation and radiocaesium was measured in 5 ml of the red blood cell ( R B C ) suspension. Live monitoring measurements were performed to document radiocaesium levels in meat. All experimental animals were weighed on the days of sampling. Vegetation samples were obtained from six exclosure cages on pasture A, and from two grazed locations
g
1500
1000 m
~
5oo
0
14 28 Pasture A
42
56
70 84 Pasture 13
Time (d)
Fig. 1. Radiocaesium content in mixed species samples from pasture A (from d 0 to d 28 of the experiment) and pasture B (from d 28 to d 84 of the experiment).
on pasture B. Mixed species samples were taken every 14 d, dried at 65°C for 2 days and ground to pass through a 1 mm sieve. Aliquots of 4 - 8 g were analysed for radiocaesium content. Radiocaesium in milk, blood and vegetation was measured by gamma-spectrometry, using a NaI(TI) scintillation detector (Packard Minaxi auto gamma5000 series). Blood samples were counted for 50 min and milk and vegetation for 30 min. The measurements were made by the Isotope Laboratory at The Agricultural University of Norway. A portable counter (Canberra Series 10 plus with a 7.5 cm N a I ( T I ) scintillator) was used for the live monitoring measurements (Strand and Brynhildsen, 1990). Aggregated transfer coefficient for radiocaesium to meat and milk was estimated as the ratio Bq k g - ~ meat or milk/deposition Bq m 2. The transfer coefficients from vegetation to meat ( F r v a l u e s ) were estimated as Bq k g - i m e a t / B q d - J ( W a r d and Johnson, 1986). Differences in radiocaesium activity concentrations between the two groups were compared using one way analysis of variance (SAS, 1990).
H.S. Hansen et al. / Small Ruminant Research 14 (1994) 199-204
3. Results
Vegetation The radiocaesium content of mixed species samples were 4 2 0 + 160 Bq kg-~ DM on pasture A and 2730+340 Bq k g - ' DM on pasture B (Fig. 1). No significant changes in radiocaesium levels were observed with time during the periods when the two pastures were used.
Ewes Radiocaesium levels in milk were 6-times higher when ewes were grazing pasture B than pasture A, equivalent to the magnitude of difference in radiocaesium levels in the two pastures. Mean milk radiocaesium levels in the control and AFCF group were stable after 14 d on pasture B (control group 4 6 0 + 124 Bq 1-' and AFCF group 110+65 Bq l -l, P < 0 . 0 5 , Fig. 2). The mean aggregated transfer coefficient to milk in control group was 11 x 10 - 3 m 2 ! -~. Meat radiocaesium levels measured by live monitoring showed the same pattern with stable values for ewes in the two groups 28 d after moving to pasture B. Mean radiocaesium concentration in the control group levelled out at 1000 Bq k g - ' . The AFCF group had throughout the experiment a stable mean radiocaesium
201
concentration which was 70% lower than the control group (P < 0.05, Fig. 3). The mean aggregated transfer coefficient to meat in the control group was 23 × 10-3 m2 k g - ' Radiocaesium levels in RBC were below the limit of detection until d 42. The level in the control ewes increased from d 42 to d 56 and plateaued at 99 + 62 Bq 1- '. Ewes in the AFCF group had mean RBC radiocaesium levels 75% lower ( 2 5 + 2 0 Bq 1-1, Fig. 4). Due to large variation between animals this difference was significant only at d 70. Ewes in the control group weighed 70.2 + 9.6 kg at the start of the experiment and 68.0+ 10.2 kg at the end. Ewes in the AFCF group weighed 69.7 + 9.5 kg at the start and 65.3 -t- 10.2 kg at the end of the experiment. Lambs Radiocaesium content in lamb's meat was 6-7-times higher after 28 d of grazing pasture B compared to pasture A. On d 28 of the experiment the control lambs had lower mean radiocaesium concentration in meat than the AFCF lambs (P<0.05, Fig. 3). After 4 wk on pasture B the lambs in the control group had mean radiocaesium concentrations of 1300-1500 Bq kg-~. 2000 o • [] •
800 o Control • AFCF group
700
Control e w e s Ewes fed AFCF Control lambs Lambs of e w e s fed AFCF
1500 6OO
~oo =_
£
~,
E .c_
300
o
1000
4O0
o
500
r.,,200
cl~ IO0 0 0
I
I
I
10
20
30
I
I
40 50 Time (d)
I
I
I
60
70
80
0 90
Fig. 2. Radiocaesium concentration in milk from ewes grazing on contaminated pasture A and pasture B as in Fig. 1. Mean and SD of six ewes fed caesium binder ( A F C F group) and seven control ewes.
10
20
30
40 50 Time (d)
60
70
80
90
Fig. 3. Radiocaesium concentration in meat measured by live monitoring. The animals were grazing on contaminated pasture A and pasture B as in Fig. 1. Mean and SD of six ewes fed caesium binder ( A F C F group), their twin lambs and seven control ewes with their twin lambs.
202
H.S. Hansen et a l . / Small Ruminant Research 14 (1994) 199-204
OControl e w e s e E w e s fed AFCF [] Control Iambs mLambs of ewes fed AFCF
200
150 ,-t"
"i
1 O0
o rr
50
0 40
I
I
I
I
50
60
70
80
90
Time (dl
Fig. 4. Radiocaesium concentration in red blood cells (RBC) in ewes and lambs grazing pasture B. Mean of six ewes fed caesium binder (AFCF group) and their twin lambs, and seven control ewes and their twin lambs.
Lambs in the AFCF group did not differ significantly from the control lambs when grazing pasture B (Fig. 3). Lambs accumulated about 25% more radiocaesium per kg BW than the control ewes did. The aggregated transfer coefficient for lambs was 31 × 10 -3 m 2 k g - ~. The Ff-value on d 84 for lambs from both groups was estimated at 1.0 d kg ~ based on consumption of 0.5 kg DM pasture and negligible amounts of milk (Table 1). Measurements of radiocaesium in RBC in lambs were below the limit of detection until d 42. These RBC values increased from 70-80 Bq 1- ~measured on d 42 to 120-140 Bq 1- ' from d 56 and through the end of the experiment ( P > 0.05, Fig. 4), Lambs in the control group increased BW from 12.6 + 2.1 kg to 29.5 _ 4.5 kg and the AFCF group from 13.0___ 1.5 kg to 28.8___4.8 kg from start to end of the experiment. This equalled a growth rate of 190 g d and 200 g d ' for the control and AFCF group, respectively.
4. Discussion The accumulation of radiocaesium in lambs is determined by the total intake of contaminated feed and the
absorption of the ingested radiocaesium. In 7-wk-old lambs the radiocaesium intake from milk was estimated to be 38% of the total intake in control lambs, and 12% in the AFCF Iambs (Table 1). Meat radiocaesium levels were also significantly different between the two groups at 7 wk of age. This showed that milk derived radiocaesium was the major source of radiocaesium accumulation in young lambs up to 7 wk of age. When grazing pasture B the milk derived radiocaesium intake was estimated to decrease from 27% to 13% in the control lambs and from 7% to 3% in the AFCF lambs from d 42 to d 70 in the experiment. In these calculations similar feed energy intakes between the two groups were assumed, because all lambs grazed the same pasture and had about the same mean growth rates. Somewhat higher absorption of radiocaesium from milk than from vegetation has been reported in lambs ( 100% vs. 85%, Mayes et al., 1992). The reduction in milk intake as the lambs mature implicated nevertheless that radiocaesium from vegetation is the main source of absorbed caesium. As a consequence the use of AFCF which reduced the radiocaesium level in milk by 75% did not significantly affect the accumulation of radiocaesium in lambs older than 11 wk. Mean RBC radiocaesium levels showed the same relations between the two groups of lambs and the two groups of ewes as the results from milk and meat. However, the variation between animals was greater for the RBC measurements and significant difference was found only between the two groups of ewes for d 70. These findings are in agreement with results from a field study involving 130 lambs where no difference between lambs of ewes treated with caesium binders and lambs of untreated ewes were observed (H.S. Hansen, unpublished data). The 5-7-fold increase in radiocaesium accumulation in milk and meat (Figs. 2 and 3) after d 28 was likely to be a response to the 6-fold increase in raqliocaesium concentration in the vegetation from pasture A and pasture B. The aggregated transfer coefficient estimated for pasture B was found to be 25% higher for lambs than ewes, which was in agreement with results of Howard (1989) that lambs accumulate more radiocaesium per kg BW than ewes when grazing the same pasture. The Frvalue for lambs was estimated at 1.0 d k g - ', which is somewhat higher than most studies have found, but well within the range from 0.24 to 1.61 d kg '
H.S. Hansen et al. /Small Ruminant Research 14 (1994) 199-204
203
Table 1 Estimated daily radiocaesium intake from pasture and milk in lambs in the control and AFCF group Time of experiment (d )
Age of lambs ( wk )
Pasture
Milk intake" kgDMd
14 28 42 56 70
5 7 9 11 13
A A B B B
0.15 0.25 0.3 0.4 0.5
i
Bqd
i
63 105 810 1080 1350
intake ~
control
ld -~
Bqd
1.1 0.9 0.6 0.5 0.4
68 65 300 250 200
AFCF L
%oftotal
Bqd
52 38 27 19 13
17 15 60 50 40
~
%oftotal 21 12 7 4 3
Pasture A was used from d 0-28 and pasture B from d 28-84. alntake of pasture (kg DM d ~) and milk ( 1 d - ~) for lambs with a daily weight gain of 150-200 g d - ~ ( Gibbet al., 19891 ).
(Howard et al., 1987; Andersson and Hansson, 1989; Beresford et al., 1989; Howard et al., 1989) The time required to attain stable levels in radiocaesium concentration in milk ( 14 d), meat (28 d) and RBC (28 d) are generally in agreement with half-lives reported in the literature (Shannon et al., 1965; Assimakopoulos et al., 1987; Howard et al., 1987; Hove and Ekern, 1988; Martin et al., 1989).
5. Conclusion When ewes and lambs graze together on pastures contaminated with radiocaesium, milk was the major source for radiocaesium accumulation in lambs younger than 6-7 wk. However, when lambs were ready for slaughter at the age of 15-20 wk, pasture radiocaesium would almost exclusively determine meat radiocaesium levels. Caesium binders given to ewes will only affect the radiocaesium content of lambs when the lambs are young. 6. Acknowledgement The authors acknowledge the financial support for this study from the Norwegian Agricultural Research Council.
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