The Influence of Supplements of Selenite, Selenate and Selenium Yeast on the Selenium Status Ofdairy Heifers

Acta vet. scand. 1999,40. 23-34.

The Influence of Supplements of Selenite, Selenate and Selenium Yeast on the Selenium Status ofDairy Heifers

By K. Ortman',R. Andersson' and H. Holst'

'Department of Animal Environment and Health, Section of Field Research, and 2Department of Clinical Chemistry, Faculty ofVeterinary Medicine , Swedish University ofAgricultural Sciences, Uppsala, Sweden.

Ortman K, Andersson R, Holst H: The influence of supplements of selenite, sele• nate and selenium yeast on the selenium status of dairy heifers. Acta vet. scand. 1999,40,23-34. - The aim ofthe study was to define possible differences between se• lenite, selenate and selenium yeast on various aspects ofselenium status in growing cat• tle. Twenty-four Swedish Red and White dairy heifers were fed no supplementary sele• nium for 6 months. The basic diet contained 0.026 mg selenium/kg feed dry matter (DM) . After the depletion period the animals were divided into 4 groups; group I-III re• ceived 2 mg additional selenium daily as sodium selenite , sodium selenate, and a sele• nium yeast product , respectively. Group IV,the control group, received no additional se• lenium. The total dietary selenium content for groups I-III during the supplementation period was 0.25 mglkg DM. After the depletion period the mean concentration ofsele• nium in blood (640 nmol/l) and plasma (299 nmol/l) and the activity ofGSH-Px in ery• throcytes (610 jlkat/I) were marginal, but after 3 months ofsupplementation they were adequate in all 3 groups . The concentration of selenium in blood and plasma was sig• nificantly higher in group III than in groups I and II, but there was no significant differ• ence between groups I and II. The activity ofGSH-Px in erythrocytes did not differ be• tween any of the supplemented groups . The animals in the control group had significantly lower concentrations ofselenium in blood and plasma and lower activities ofGSH-Px in erythrocytes than those in the supplemented groups . The activity ofGSH• Px in platelets was also increased by the increased selenium intake. There was no dif• ference in the concentration oftriiodothyronine (T3) between any ofthe groups, but the concentration ofthyroxine (T4) was significantly higher in the unsupplemented control group .

cattle; feed supplements; sodium selenite; sodium selenate; GSH-Px; plasma; blood; platelets; thyroxine; triiodothyronine.

Introduction Sweden is a selenium deficient country and use of sodium selenite has been questioned commercial feeds for farm animals have been (Pehrson 1993b), principally because the selen• routinely supplemented with selenium since ite ion has pro-oxidative properties (Hafeman et 1980. By tradition, but also for economic rea• al. 1974, Dougherty & Hoekstra 1982, Levan• sons, sodium selenite has been the selenium der & Burk 1986, Spallholz 1994). Its in vivo compound used. However, in recent years the disadvantages have been highlighted in experi-

Acta vet. scand. vol. 40 no. I, 1999 24 K. Ortman et al. ments with mice and rats (Dougherty & Hoek studies on platelets have been done in rats or stra 1982, Csallany & Menken 1986). As an al• human beings (Levander et al. 1983a, Levander ternative to selenite, organic selenium com• et al. 1983b, Kiem 1988), and to the authors ' pounds have been tested and found to be knowledge no study has been made in cattle . appropriate for the supplementation of dairy In recent years several new specific selenopro• cows (Ortman & Pehrson 1997). However, or• teins have been identified (Zachara 1992). One ganic selenium compounds are more expensive of them is the enzyme type I iodothyronine than inorganic selenium compounds. deiodinase, which converts thyroxine (T4) to Sodium selenate is an inorganic selenium com• the more active triiodothyronine (T3). Arthur et pound which is similar in price to sodium se• al. (1988) reported that severely selenium-defi• lenite, and has the potential advantage that the cient calves had higher plasma T4 concentra• selenate ion does not have the pro-oxidative tions and lower plasma T3 concentrations than properties of selenite. Kumpulainen et al. calves which had been supplemented with sele• (1985) proposed that selenate should be used to nium. supplement human diets to avoid the disadvan• The present study had 3 main objectives: tages ofselenite. - to determine whether there were any diffe• When evaluating the biological effect ofa sele• rences between the concentrations of selenium nium compound, it is generally accepted that in blood and the activities of GSH-Px in the the concentration ofselenium in different body erythrocytes of cattle supplemented with tissues may not adequately represent the con• sodium selenite, sodium selenate or a selenium centration ofthe biologically active selenium in yeast product , those tissues . Instead, the activity of the sele• - to investigate whether the determination of nium-containing enzyme glutathione peroxi• the GSH-Px activity of the platelets of cattle dase (GSH-Px) has been commonly used as an would be a satisfactory method for the evalua• indicator of the active component of the sele• tion oftheir short-term selenium status, nium in different tissues . Most often the activ• - to investigate whether the metabolism of the ity of GSH-Px in blood has been used as long• thyroid hormones T3 and T4 would be influ• term indicator of selenium status and the enced by the form of supplementary selenium activity of GSH-Px in serum or plasma as a given. short-term indicator. However, in cattle the ac• tivity of GSH-Px in serum is very low and therefore not a suitable parameter (Carlstrom Materials and methods 1979). Levander (1983) emphasised the value The experimental protocol used in this study ofusing the activity ofGSH-Px in platelets as a was approved by the local ethical committee. short-term indicator of the selenium status of human beings, because platelets are turned over Animals and management rapidly and have a high selenium content. The Twenty-four Swedish Red and White dairy concentration of selenium in platelets adapts heifers were used; in September 1995 they were quickly to the dietary intake ofselenium, and in tied up in a long-stall system, and were divided that respect they are comparable to the liver, into 4 groups of 6 animals whose mean ages which has been reported to contain the largest (and ranges) were as follows: group I, 17 pool of labile selenium in the body (Thompson months (11-25) ; group II, 17 months (11-22) ; et al. 1980, Levander et al. 1983b). Most ofthe group III, 17 months (11-23) ; and group IV, 17

Acta vel. scand. vol. 40 no. 1, 1999 Selenium in dairy heifers 25 months (I 1-22). The groups were randomly mglkg OM) for group IV. The overall experi• allocated to one of 4 treatments. For the 6 mental design is summerised in Fig. I. months from September 1995 to the end of February 1996, the 4 groups were fed the same Samples basic ration, to which no selenium was added, Jugular blood samples were taken from all the except for the 4 youngest heifers, one in each heifers one and 2 weeks before the start of the group, which were not brought to the farm un• supplementation period (in the Figs. 2-7 the til mid-October and were therefore fed the ba• mean value ofeach ofthe parameters measured sic diet for only four-and-a-halfmonths instead in these 2 samples is presented as the zero-time of6. From the end of February until the end of value) and then at pre-determined intervals dur• May groups I, II and III were fed rations sup• ing the experiment. All the samples were taken plemented with selenium in the 3 different between 7 and 8 a.m. The anticoagulants used forms, while group IV remained on the unsup• were potassium-EOTA for the determination of plemented diet. GSH-Px activity in erythrocytes and selenium in whole blood and plasma, sodium citrate for Feeding and treatments the isolation of platelets, and sodium heparin The basic diet, which was fed individually for the determination ofT4 and T3 in plasma. during the whole indoor season, was composed The blood samples were brought to the labora• of grass silage fed ad libitum, I kg oat grain, tory within one hour after collection and, ifnec• and 100 g of a selenium-free vitaminised min• essary, centrifuged immediately. The platelets eral feed daily. Each animal was estimated to were isolated and their GSH-Px activity was de• consume 8 kg of silage dry matter (OM) per termined on the day of sampling , but all the day. The silage contained 0.023 mg Selkg OM other samples were stored at - 20 °C until ana• and the oat grain contained 0.06 mg Selkg OM. lysed. The average daily intake of selenium from the basic diet was thus 0.238 mg (0.026 mglkg Laboratory analyses OM). The sodium selenite, sodium selenate and For the isolation of platelets 20 ml of the cit• the selenium yeast product (ALKOSEL 1000, rated blood was transferred into a round-bot• Primalco Ltd Biotec, Rajamaki, Finland) were tomed 25 ml glass tube containing 5 ml ofacid• each mixed with solid glucose so that a known citrate-dextrose solution (ACO). After centri• volume (I5 ml) contained 2.0 mg selenium . fugation at 220xg for 30 min at 25°C the Group I received sodium selenite, group II re• plateletrich supernatant was transferred into ceived sodium selenate and group III received coned 10 ml polystyrene tubes. After additional the selenium yeast product. Group IV remained centrifugation at 1400xg for 30 min at 4°C the as an unsupplemented control group . The glu• pellet containing the platelets was resuspended cose-selenium mixture containing 2 mg sele• in a fixed volume of calcium-free phosphate nium was given to each ofthe heifers in groups buffer and the platelets were counted manually I-III on their grain once a day, and the animals in a Biirker chamber. After counting, the in group IV were given the same volume ofglu• washed platelets were centrifuged at 1500xg for cose, without added selenium, in the same way. 20 min at 4 °C, lysed in distilled water, and cen• The total selenium content of the supplemented trifuged at a maximum speed of 21,500xg for ration was thus 2.24 mg (0.25 mglkg OM) for 10 min at 4 °C to pellet the cell debris. The en• groups I-III, and remained at 0.24 mg (0.026 zyme-containing supernatant was used to as-

Acta vel. scand. vol.40 no. 1, 1999 26 K. Ortman et al.

----••+-- 0.03 + 0.22 ppm Se-+ I I Group I, II and III

----••.- 0.03 ppm Se ----+ I I Group IV

... ------)(..I-)QQ()(--...-- .... Sept 1995 Febr 1996 May 1996

Figure I . Overall experimental design. Basic feed contained 0.03 mg Selkg (ppm). During the eleven weeks period from Februaryto May 1996groups I-IIIwere supplementedwith 0.22 ppm Se as sodium selenite, sodium selenate and selenium yeast, respectively.Group IV was an unsupplementedcontrol group. • denotes time of sampling. sess the GSH-Px activity. Typically, the method house methods, serial dilutions of plasma with yielded 100-300 x 106 platelets/ml of citrated high concentrations of T3 and T4 were pre• blood; however, 5 animals, from 4 different pared and were shown to produce displacement groups, never yielded enough platelets for the curves parallel to the respective standard measurements ofGSH-Px and they were there• curves. For T3, the intra- and inter-assay coeffi• fore excluded from this part ofthe experiment, cients of variation for a quality control sample leaving 19 animals. were 3.3% and 5.3% (mean = 2.6 nmol/l), re• The GSH-Px activity in erythrocytes and plate• spectively. For T4 the intra- and inter-assay co• lets was measured by the method described by efficients ofvariation for 2 quality control sam• Paglia & Valentine (1967). ples were 2.3% and 6.6% (mean = 37.4 nmol/I), Before the selenium content ofthe samples was and 5.2% and 7.5% (mean = 175 nrnol/l). measured they were ashed with nitric acid in closed containers, using a microwave digestion Statistical analys es procedure with a final temperature of 190 °C The experiment was designed as a randomised (Matusiewicz et al. 199 I). After digestion the block trial. For the GSH -Px activity oferythro• samples were treated with hydrogen peroxide cytes and the selenium concentration of whole and hydrochloric acid as described by Alfthan blood, a regression line, with time as the inde• (1984), and then diluted 50: I with a 20% solu• pendent factor and GSH-Px activity or blood tion ofurea and allowed to stand for 30 min. The selenium as the dependent factor, was fitted to concentration of selenium was finally deter• the results from each animal, and the value of mined by atomic absorption spectrophotometry the mean slope for each group was calculated. ofthe hydride, as described by Sturman (1985). For plasma selenium, the mean concentration Plasma total T4 and T3 concentrations were de• observed during a period when the concentra• termined by using commercial solid-phase ra• tion had reached a plateau was calculated for dioimmunoassay kits with 1251 as tracer (Coat• each group. The differences between the groups a-Count, Diagnostic Products Corporation, Los were compared by means of a two-way Angeles, CA, USA). The method has been val• ANOVA, followed by multiple comparisons idated for bovine plasma T3 and T4 by Williams with a 95% simultaneous degree ofconfidence, et al. (1987). To confirm the accuracy ofthe in- according to the method ofTukey.

Act a vet. scand. vol. 40 no. 1. 1999 Selenium in dairy heifers 27

2500

-group I 2000 ...... group II S-o ...... groupIII -groupN ! 1500 ."§ 11" ." 0 1000 :c0 "0" ..c 500

0 0 2 4 6 8 10 Weeks Figure 2. The concentration of seleniumin whole bloodof heifersduring II weeksof supplementation with 2 mg seleniumdaily as sodiumselenite(group I), sodiumselenate(group II), or seleniumyeast(group III) and in unsupplemented controlanimals(group IV).

The differences between groups for the concen• tion decreased slightly during the trial. The dif• tration ofT4 in plasma and the activity ofGSH• ferences between the groups were significant, Px in platelets was calculated by using the Gen• except for that between the selenite and sele• eral Linear Models procedure of SAS (SAS nate groups. Institute Inc. 1988). The calculations were ba• The concentration of selenium in plasma in• sed on the results ofall the samples taken after creased in all the supplemented groups and the difference between the supplemented reached a plateau after 4 weeks of supplemen• groups and the control group was considered to tation in groups II and III and after 6 weeks in have been established. The independent vari• group I (Fig. 3) . The differences between the ables used were treatment (selenite, selenate, groups during the plateau period were signifi• selenium yeast, control), occasion of sampling cant except for that between the selenite and se• and block . However, block was not included for lenate groups. the activity ofGSH-Px in platelets, because the The activity of GSH-Px in erythrocytes in• blocks were incomplete owing to the missing creased in all the supplemented groups but did values. not reach a plateau during the experiment (Fig . 4). In the control group the activity de• creased slightly. There were no significant dif• Results ferences between the selenium-supplemented The concentration of selenium in the whole groups, but all the supplemented groups had blood ofall the supplemented groups increased significantly higher GSH-Px activities than the during the trial and had not reached a plateau control group. after II weeks of supplementation (Fig. 2); in The activity of GSH-Px in platelets increased contrast, in the control animals, the concentra- during the first 3 weeks of supplementation, but

Acta vet. scand. vol. 40 no. I. 1999 28 K. Ortman et al.

1200

1000

"0 -E 800 -5. --group I E ...... group II 600 'c" ...... group III '" --group IV «l 400 a::«l

200

0 0 2 4 6 10 Weeks Figure 3 . The concentration ofselenium in plasma of heifers during II weeks ofsupplementation with 2 mg selenium daily as sodium selenite (group I), sodium selenate (group II), or selenium yeast (group III) and in un• supplemented control animals (group IV).

2500

--group I 2000 ---group II ...... group III S«l -" -group IV

1500 "-" :i: VJ 0 s, 1000 '"u

E> t.Ll 500

0 0 2 4 6 8 10 Weeks

Figure 4 . The activity of GSH-Px in erythrocytes of heifers during II weeks ofsupplementation with 2 mg selenium daily as sodium selenite (group I), sodium selenate (group II), or selenium yeast (group III) and in un• supplemented control animals (group IV). then reached a plateau (Fig. 5). The activity in the had a significantly higher GSH-Px activity than group supplemented with selenium yeast (III) the control group, but was not significantly dif• was then significantly higher than in the other ferent from the group supplemented with selen• groups. The group supplemented with selenate ite, which did not differ from the control group.

Acta vel. scand . vol. 40 no. 1. 1999 Selenium in dairy heifers 29

0.03 ,------,

-.; :;; 0. '0 0.02 -;:, -'" " e,>< :i: 0.01 -'-group I ...... groupII u" --group III 0.005 £ --group IV

O+------+-----+-----+------+-----+------l o 2 4 6 8 10 12 Weeks

Figure 5. The activity ofGSH-Px in platelets ofheifers during II weeks ofsupplementation with 2 mg sele• nium daily as sodium selenite (group I), sodium selenate (group II), or selenium yeast (group III) and in unsup• plemented control animals (group IV).

2.5

2 -

S 0 E 1.5 .s.., I- -'-group I ...... groupII " ee -0-group III ii: -+-group IV 0.5

0 0 2 4 6 8 10 Weeks

Figure 6 . The concentration oftriiodothyronine (T3) in plasma ofheifers during II weeks ofsupplementation with 2 mg selenium daily as sodium selenite (group I), sodium selenate (group II), or selenium yeast (group III) and in unsupplemented control animals (group IV).

There were no significant changes in the con• first 2 weeks after the period of selenium sup• centration of T3 in the plasma of the 4 groups plementation began, but increased again until during the trial (Fig. 6). However, the mean the end of the trial (Fig. 7). On the basis of the concentration of plasma T4 decreased in the samples taken 6 and II weeks after supplemen-

Acta vel. scand. vol. 40 no. 1, 1999 30 K. Ortman et al.

60 S 0 E 5- 50 -e- --group I I- 40 ---group II '" --group III 30 c::'" --group IV 20

0 0 4 6 10 Weeks

Fig ure 7. The concentration of thyroxine (T4) in plasmaof heifersduring II weeksof supplementation with 2 mg seleniumdaily as sodiumselenite(group I), sodiumselenate(group II), or seleniumyeast(group III) and in unsupplemented control animals(group IV). tation with selenium began, all the supple• After II weeks of supplementation with either mented groups had significantly lower concen• sodium selenite, sodium selenate or the sele• trations ofT4 in plasma than the control group, nium yeast product the animals in groups I, II but they were not significantly different from and III had whole blood and plasma selenium each other. concentrations and erythrocyte GSH-Px activi• ties within adequate ranges, while the selenium status of the animals in the control group had Discussion not changed. In the supplemented animals the After being fed the selenium-deficient diet for 6 plasma selenium concentration reached a pla• months the mean whole blood selenium con• teau, but the whole blood selenium and the ac• centration ofall the 24 animals was 640 nmolll tivity of GSH-Px in erythrocytes did not. This (range: 344 -I 088) , their mean plasma selenium difference might have been due to the relatively concentration was 299 nmolll (range: 191-381) short experimental period; the life-span ofery• and the mean activity of GSH-Px in their ery• throcytes is about 160 days and as a result these throcytes was 611 jlkat/I (range: 206-1059). parameters should not have reached a plateau These values indicate that most of the heifers until all the red blood cells from the depletion were either deficient or had a marginal sele• period had been replaced. Whole blood sele• nium status, and that some of them might have nium and the activity of GSH-Px in erythro• been at risk of nutritional muscle degeneration cytes are therefore suitable for monitoring (Pehrson 1993a). Thus, the animals were in a long-term selenium status, whereas plasma se• condition comparable with that of animals in lenium concentration, which reached a plateau Sweden before 1980, when animal feedstuffs within 6 weeks, should be more suitable for were not supplemented with selenium. monitoring short-term selenium status.

Acta vet. scand . vol. 40 no. I. 1999 Selenium in dairy heifers 31

There was a clear difference between the effi• any of the other supplemented groups , The ex• cacy of the organic and inorganic selenium periment therefore provided no further evi• compounds as selenium supplements with re• dence that selenite has a pro-oxidative effect spect to blood and plasma selenium concentra• when fed to cattle at a dose corresponding to tions; the animals that received the selenium 2 mg ofselenium daily. yeast had higher concentrations ofselenium in The results also provided evidence that there whole blood and plasma than the animals sup• was no difference between the efficacy of se• plemented with selenite and selenate . These re• lenite and selenate as selenium supplements for sults are in accordance with earlier experiments cattle, whether the parameter considered was (Nicholson et al. 1991, Ortman & Pehrson selenium in whole blood, selenium in plasma, 1997). There was also a tendency for the sele• the activity of GSH-Px in erythrocytes or nium yeast group to have a higher activity of platelets, or the concentrations of T3 or T4 in GSH-Px in their erythrocytes than the other plasma, In contrast, Podoll et al. (1992) re• supplemented groups, although the difference ported significantly higher serum selenium was not significant. However, the experiment concentrations when dairy cattle were supple• ended before the GSH-Px activity had reached mented with selenate rather than selenite, al• a plateau and it is possible that the difference though the difference was small. Henry et al. might have become significant if a plateau had (1988) also found that selenate had a higher been reached. Earlier findings in ruminants bioavailability than selenite when it was fed to have been variable; Pehrson et al. (1989), young wethers, but they used a dose of6 mg/kg Nicholson et al. (1991) and Malbe et al. (1995) dietary DM, which is considered to be toxic observed higher activities of GSH-Px in cattle (Sandholm 1993). On the other hand, Serra et supplemented with organic selenium than in al. (1994) found that selenite and selenate were cattle supplemented with inorganic forms ofse• absorbed and retained equally well when they lenium, whereas Ortman & Pehrson (1997) ob• were used to supplement young wethers with served no difference . physiological doses ofselenium. Even if the po• One reason for suspecting that selenite has a tentially adverse effects ofthe oxidative proper• pro-oxidative effect has been the reports of in• ties of selenite on farm animals remain uncer• creased activities ofGSH-Px when selenite has tain, it seems evident that sodium selenate is a been fed in higher than optimal doses, even up satisfactory alternative to sodium selenite, to toxic levels (Hafeman et al. 1974, Oh et al. since it is at least as effective in improving the 1976, Pehrson & Johnsson 1985). It has been selenium status ofyoung cattle. suggested that this effect may indicate that high Levander (1983) found that the activity of doses of selenite increase the activity of GSH-Px in platelets could be used to assess the GSH-Px in order to counteract the pro-oxida• short-term selenium status of human beings tive properties ofthe compound. If this was the and rats, The results ofthis experiment indicate case it would be expected that animals fed se• that the activity of GSH-Px in platelets should lenite would have higher activities of GSH-Px also be useful for monitoring the selenium sta• than animals fed organic selenium or selenate, tus of cattle, and that, in terms of this parame• which should not have any pro-oxidative prop• ter, the selenium yeast had the highest bioavail• erties. However, in this experiment there was no ability. However, the levels of enzyme activity tendency for the animals fed selenite to have were probably close to the lower detection limit higher GSH-Px activities than the animals in of the assay and the measurements were very

Act a vct. scand. vol. 40 no, 1. 1999 32 K. Ortman et al.

variable . The results must therefore be inter• cantly higher in the unsupplemented control preted with caution. Improvements to the group than in the supplemented groups, but method, for example by improving the proce• there were no differences between the supple • dure for lysing the platelets, and by adapting the mented groups. In contrast, the concentrations method of Paglia & Valentine (1967) to the ofT3 were very similar in all 4 groups. It is pos• lysate, would probably give a method with sible that there are compensatory systems greater validity and precision and consequently which actively maintain the concentration of more reliable results. the more metabolically active hormone T3 Rey et al. (1994) reported that in selenium-defi• nearly constant. For example, the activity ofthe cient human beings platelets were abnormally enzyme iodothyronine deiodinase is actually aggregatable, because of the functional role of induced in selenium-deficient animals, despite GSH-Px in the production of thromboxan Az. it being a selenium-containing enzyme, and As a result, in selenium-deficient subjects , the moreover, the degradation ofT3 to T2 becomes platelets might aggregate and sediment during inhibited when the supply of selenium is lim• the initial centrifugation and few platelets would ited (Arthur 1993). This suggests that the ani• be obtained. However, the 5 heifers in this study mals in the control group were only marginally which consistently gave poor yields ofplatelets deficient , rather than severely deficient in sele• were distributed among the 4 groups, and the nium . poor results therefore seem not to have been as• In conclusion, organic selenium as a yeast prod• sociated with their selenium status. uct increased the selenium concentration in The activity of GSH-Px in the platelets tended blood and plasma more efficiently than selenite to reach a plateau after 3 weeks of selenium or selenate, but no difference was found be• supplementation, whereas the plasma selenium tween organic and inorganic compounds in concentration reached a plateau within 6 weeks. their capacity to increase GSH-Px activity in However, the small difference between the time blood or to influence the T4 levels. No differ• at which these 2 parameters reached a plateau, ence in bioavailability was found between se• and the difficulties experienced in measuring lenite and selenate. platelet GSH-Px activity suggests that at pre• sent plasma selenium remains preferable for monitoring the short-term selenium status of Acknowledgements cattle . However, GSH-Px activity is a more sat• The authorsare indepted to Dr. Bo Pehrson for help isfactory indicator of the biologically active in planning and preparing the study, to Mats Car• lquist for help in the bam, and to Lactamin AB and pool ofselenium, and as the activity ofGSH-Px Primalco Ltd Biotec for the supply of the selenium in bovine plasma is very low, the measurement compounds. The study was financially supported by of GSH-Px activity in platelets might have the Swedish Farmers' Foundation for Agricultural some advantages for assessing the short-term Research. selenium status of cattle, provided that the method can be improved adequately. The metabolism of thyroid hormones was af• References fected by the low selenium diet in this study, A/fthan G: A micromethod for the determination of selenium in tissues and biological fluids by although the selenium status ofthe control ani• single-test-tube fluorimetry. Anal. Chim. Acta mals was better than in the trial ofArthur et al. 1984, /65 . 187-194. (1988). The concentration of T4 was signifi- Arthur JR: The biochemical functions of selenium:

Acta vel. scand, vol. 40 no. 1. 1999 Selenium in dairy heifers 33

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glutathione peroxidase from human blood Sammandrag platelets. Age-related changes in the enzyme. EjJekten av tillfbrsel av selenit, selenat och selenjiist Biochim. Biophys. Acta 1994, 1226. 219-224. po kvigors selenstatus. Sandholm M: Acute and chronic selenium toxicity. Norw. 1.agric . Sci. 1993, Suppl. 11, 37-50. Under en sexmanaders period gays 24 rekryterings• SAS Institute Inc.: SAS/STAT users guide release kvigor en icke- selenberikad foderstat innehallande 6.03 Ed. SAS Institute Inc., Cary NC, USA. 0,026 mg selenlkg torrsub stans (ts). Djuren delades 1988. darefter in i 4 grupper. Grupp I erholl under 3 rna• Serra AB. Nakamura K. Matsui t; Harumoto r. Fuji nader via fodret ert dagligt tillskott pa 2 mg selen i hara T: Inorganic selenium for sheep 1.Selenium form av natriumselenit. Grupp II gays samrna mangd balance and selenium levels in the different selen som natriumselenat och grupp III samma ruminal fluid fractions. AJAS 1994, 7, 83-89. mangd organiskt selen i form av ett selenjastpreparat, Spallholz JE : On the nature of selenium toxicity Grupp IV (kontrollgruppen) erholl inget selentill• and carcinostatic activity. Free Radic. BioI. Med. skott. Det totala seleninnehallet i de berikade foder• 1994, 17. 45-64 staterna var 0,25 mg/kg ts. Nar selensupplernenterin• Sturman BT: Development of a continuous-flow gen paborjade s var seleninnehallet i helblod och hydride and mercury vapor generation accessory plasma 640 resp. 299 nmol/l och GSH-Px aktiviteten for atomic absorption spectrophotometry. Appl. i erytrocyterna 610 Ilkat/I, vilket innebar att djuren Spectrosc. 1985, 39, 48-56. hade ett selenstatus som lag nara bristnivan, Vid Thompson KG, Fraser Al, Harrop BM, Kirk JA: forsokets slut hade samtliga supplementerade grup• Glutathione peroxidase activity in bovine serum per elt fullgott selenstatus, medan inga forandringar and erythrocytes in relation to selenium concen• hade skett i kontrollgruppen. Djuren i grupp III hade .trations of blood, serum and liver. Res. Vet. Sci. vid forsokets slut signifikant hogre halt av selen i 1980, 28, 321-324. blod och plasma an de i grupp l och II, under det att Williams JE. Miller SJ. Mollet TA, Grebing SE, inga skillnader forelag betraffande GSH-P x aktivi• Bowman DK. Ellersieck MR: Influence of frame teten i erytrocyter. size and zeranol on growth, compositional GSH-Px aktiviteten i trombocyter okade ocksa efter growth and plasma hormone characteristics. 1. selentillfcirseln. Det forelag ingen skillnad mellan na• Anim. Sci. 1987, 65. 1113- 1123. gra grupper vad avser trijodtyronin (T3) i plasma, Zachara BA: Mammalian sclenoproteins. 1. Trace daremot hade kontrollgruppens djur en signifikant Elem. Electrolytes Health Dis. 1992, 6. 137-151. hogre halt av thyroxin (T4) i plasma.

(Rece ived July 10. 1998; accepted November II, 1998).

Reprints may be obtained from: K. Ortman, Department of Animal Environment and Health, Section of Field Research, Faculty of Veterinary Medicine, Swedish University of Agrucultural Sciences, P.O. Box 234, S-532 23, Skara, Sweden. E-mail: K.Ortman@hmh .slu.se, tel: +46-5 11 67 000, fax: +46-511 67 134.

Acta vet. scand. vol. 40 no. 1. 1999