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Livestock Science

Livestock Science 155 (2013) 255–261

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Effects of trace element supplementation on apparent nutrientdigestibility and utilisation in grass-fed zebu(Bos indicus) cattle

V. Dermauwa,n, K. Yisehak b, E.S. Dierenfeld c, G. Du Laing d, J. Buyse e,B. Wuyts f, G.P.J. Janssens a

a Laboratory of Animal Nutrition, Faculty of Veterinary Medicine, Ghent University, Heidestraat 19, B-9820 Merelbeke, Belgiumb Department of Animal Sciences, Jimma University College of Agriculture and Veterinary Medicine, PO Box 307, Jimma, Ethiopiac Zootrition Consulting, LLC, 4736 Gatesbury Drive, St. Louis, MO 63128, USAd Department of Applied Analytical and Physical Chemistry, Ghent University, Coupure Links 653, B-9000 Ghent, Belgiume Department of Biosystems, Laboratory of Livestock Physiology, K.U. Leuven, Kasteelpark Arenberg 30, B-3001 Leuven, Belgiumf Department of Clinical Chemistry, Laboratory of Metabolic Disorders, University Hospital Ghent, De Pintelaan 185, B-9000 Ghent,Belgium

a r t i c l e i n f o

Article history:Received 19 April 2012Received in revised form16 May 2013Accepted 24 May 2013

Keywords:Trace elementsSupplementationRuminantNutrient digestibility

13/$ - see front matter & 2013 Elsevier B.V. Ax.doi.org/10.1016/j.livsci.2013.05.027

esponding author. Tel.: +32 9 264 7824; faxail address: Veronique.Dermauw@ugent.be (

a b s t r a c t

Trace element deficiencies in cattle are omnipresent, both in developing and industrialisedregions. Little information is available on the effect of dietary trace elements on nutrientdigestibility and utilisation, in spite of many deficiency-related symptoms suggesting a relevantrole, such as loss of appetite in Zn deficiency and severe diarrhoea in Cu deficiency. The presentstudy aimed to identify the early effects of dietary trace elements on nutrient utilisation ingrass-fed zebu (Bos indicus) cattle. Adult bulls (n¼8) were randomly assigned to a treatment:control or trace element supplementation (Zn, Mn, Cu, Se, I and Co) during 28 days. Grassmineral analysis suggested deficient Cu (5.53–9.60 mg/kg) and Se (0.02–0.09 mg/kg) concen-trations in combination with high S (2577–3855 mg/kg) and Mo (1.52–3.12 mg/kg) and veryhigh Fe (619–1214 mg/kg) concentrations. Supplementation increased plasma Cu (0.82 vs.0.61 mg/l), Zn (1.40 vs. 0.89 mg/l), Mn (0.30 vs. 0.05 mg/l) and Se (0.07 vs. 0.06 mg/l)concentrations (all Po0.05). Faecal Cu, Zn, Mn and Se were also increased (Po0.05), as wasfaecal Co (P¼0.05) concentration in supplemented bulls. On the contrary, trace elementsupplementation did not affect plasma ceruloplasmin and superoxide dismutase activities(P40.05). Also, no effects on apparent nutrient (dry matter, ash, protein, fat, and fibre)digestibility, apparent trace element absorption (except for Se and I) or plasma acyl carnitines(indicators of available energy substrates) were observed in this study (all P40.05). Overall,despite clear improvement in trace element status – notwithstanding high concentrations of Cuantagonists in the grass diet – supplementation did not affect nutrient digestibility or utilisationin grass-fed zebu cattle.

& 2013 Elsevier B.V. All rights reserved.

1. Introduction

Studies in different regions of the world demonstratedthat the concentrations of trace elements in pasture and

ll rights reserved.

: +32 9 264 7848.V. Dermauw).

rangelands can vary considerably with season, and oftendrop to levels of concern for deficiencies in animal nutrition(Blanco-Penedo et al., 2009; Khalili et al., 1993; Khan et al.,2008). Optimal trace element supply is well known to beessential in ruminants for health and production. For exam-ple, Zn is important for reproduction and skin health, Fe foroxygen transport in the body and Cu for optimal immunity(Suttle, 2010). Several studies linked the presence of trace

Table 1Proximate, fibre and mineral analysis of the grass diet.

Parameter Experimental week§ SE P

1 2 3 4 5

(g/kg)DM 183 208 209 244 209 10 0.52(g/kg DM)Ash 131a,b 136a,b 119a,b 103b 140a 4 0.03EE 22a,b 25a 18b 16b 19a,b 1 0.01CP 133 149 137 94 132 7 0.07NDF 631 614 679 615 648 9 0.14ADF 346 319 353 355 338 7 0.59ADL 63 58 76 61 54 6 0.88(mg/kg DM)S 2601 2899 2963 2577 3855 164 0.06Mo 1.5 2.1 3.1 2.3 1.9 0.2 0.10Fe 619 2082 1214 879 777 210 0.18Mn 114b 175b 189a,b 383a 233a,b 29 0.01Zn 44a,b 53a,b 67a 34b 51a,b 4 0.04Cu 5.6b 8.6a 9.6a 5.5b 5.8b 0.5 0.001I 0.7 0.3 0.3 2.0 3.1 0.5 0.34Se 0.02 0.07 0.05 0.09 0.09 0.01 0.14Co 0.4 1.1 0.8 0.6 0.5 0.1 0.14

SE¼Standard error, DM¼dry matter, EE¼ether extract, CP¼crude pro-tein, NDF¼neutral detergent fibre, ADF¼acid detergent fibre, ADL¼aciddetergent lignin.a,bSignificantly different between weeks at Po0.05.

§ Week 1: unsupplemented grass diet in both groups, week 2–5:unsupplemented grass diet in control group, in the supplementationgroup, grass diet supplemented with a tablespoon of molasses and traceelement mix, providing (per kg DM): 30 mg of Zn, 20 mg of Mn and10 mg of Cu, as chelated-to-glycine forms, 0.10 mg of Se, as premix (allprevious: MAACs, Novus International (St.-Charles, Missouri, USA)),0.50 mg of I as KI and 0.10 mg of Co as Co(NO3) � 6H2O.

V. Dermauw et al. / Livestock Science 155 (2013) 255–261256

element deficiencies with the increased incidence of a wholerange of diseases, such as chronic metritis, subclinicalmastitis and lameness in cattle herds; these deficiencieswere more frequent when cows were not supplementedwith minerals (Guyot et al., 2009; Mulligan et al., 2006).

Certain functions of trace elements and deficiency-relatedsymptoms are specifically associated with the digestivesystem. Copper deficiency is frequently accompanied bysevere diarrhoea (McDowell and Arthington, 2005), whiledown-regulation of the Cu-dependent lysyl oxidase (EC1.4.3.13) leads to impaired cross-linking of collagen accom-panied with damaged gastro-intestinal connective tissue andulceration (Frank, 1998), which is well known in humans tobe associated with malabsorption syndrome (Jensen, 2000).Zinc on its behalf, is known to play a key role in DNAsynthesis (Miller et al., 1985) and therefore, deprivation ofthis element is most marked in rapidly dividing cells, such asintestinal cells. Consequently, Zn supplementation was ableto cure intestinal damage in rats (Tran et al., 2003). Further-more, one of the first symptoms of Zn deficiency is loss ofappetite (Suttle, 2010). Manganese is linked with lipid andcarbohydrate metabolism through the activity of pyruvatecarboxylase (EC 6.4.1.1), responsible for the conversion ofpyruvate to oxaloacetate, the latter an important intermedi-ate in the citric acid cycle, crucial in the cellular energymetabolism (NRC, 2000).

The previous paragraph suggests an important role oftrace elements in digestive system function and nutrientutilisation. However, to the best of our knowledge, littleresearch has been conducted on the degree to which traceelement status affects cattle nutrient digestibility andutilisation. One published study (Grace et al., 2002),performed with grazing horses, reported no effect of traceelement supplementation on the digestibility of proximatecomponents (Grace et al., 2002). Given the widespreadoccurrence of trace element deficiencies in grazing cattlearound the world, the described biochemical and physio-logical association of trace elements with digestive systemfunction and the lack of relevant studies in cattle, ourobjective was to evaluate the early effects of trace elementsupplementation on nutrient digestibility and utilisation ingrass-fed zebu (Bos indicus) cattle, naturally varying intrace element supply.

2. Materials and methods

2.1. Animals and housing

This study was reviewed and approved by the EthicalCommission of the Faculty of Veterinary Medicine at GhentUniversity (EC: Case 2010_102). The trial was conducted atJimma University College of Agriculture and VeterinaryMedicine, Ethiopia. Eight adult Ethiopian highland zebu(B. indicus) bulls were obtained from a local livestock market,in a region with cattle displaying trace element deficienciesas established by previous work (Dermauw et al., 2013). Allbulls were aged between 4 and 6 years (mean: 4.9year70.2) and weighted between 139 and 189 kg (mean:163 kg77). The animals had a body condition score between3 and 7 (mean: 4.670.46) on a scale of 1–9 designed forzebus (Nicholson and Butterworth, 1986). The bulls were

housed in separate stables. After arrival, the animals wereweighed and dewormed using a combination of ivermectineand clorsulon (Ivomec Fs, 0.02 ml/kg body weight, MerialAnimal Health, Brussels, Belgium) and left to adapt to thehousing conditions and diet for 1 week.

2.2. Diet and supplementation

Throughout the experimental period, all bulls received alocal grass mixture diet in order to simulate their natural dietwith varying amounts of trace elements. The quantity ofgrasses supplied to the bulls was based on 2% of theindividual body weight (McDowell, 1996), which was weeklymonitored, and an average dry matter (DM) content of 20%in the grass. The nutrient composition of grass is presented inTable 1. Baseline measurements without treatment wereexecuted in week 1. In week 2, the animals (n¼8) wererandomly allocated to a treatment: trace element supple-mentation or control. Supplementation consisted out of atrace element mix supplying per kg DM of grass: 30 mg ofZn, 20 mg of Mn, 10 mg of Cu, all as chelated to glycineMAACs; 0.1 mg Se as MAACs Se Premix (Novus Interna-tional, Inc., St. Charles, Missouri, USA); 0.1 mg of Co as Co(NO3)2 �6H2O (1025360100, Merck, Overijse, Belgium) and0.5 mg of I as KI (207969-100G, Sigma-Aldrich, Bornem,Belgium), according to the recommendations for beef cattleestablished by NRC (2000). The mineral powder was mixed

V. Dermauw et al. / Livestock Science 155 (2013) 255–261 257

with a spoon of molasses and top dressed on the offeredgrass to ensure complete intake.

2.3. Samples and storage

The experiment lasted for 5 weeks (baseline measure-ments without treatment followed by 4 treatment weeks).At the end of every week, during 3 subsequent days,apparent nutrient digestibility and apparent trace elementabsorption (see below) were estimated through totalfaecal collection: faeces were collected using faecal collec-tion bags and grass refusals were weighed. During these3 days, daily subsamples of offered grass and faeces peranimal were taken and afterwards faeces were individu-ally pooled per faecal collection period. Faecal and grasssamples were oven-dried at 65 1C for 72 h and groundthrough a 2 mm screen. From each animal, a weeklyjugular blood sample was obtained using 20 G needles(MN-2038M) and two sodium heparin tubes (VT-100SH,both Venojects, Terumo, Leuven, Belgium). Plasma wasobtained through centrifugation at 1500� g for 10 min. Allsamples were stored at −20 1C until further analysis.

2.4. Mineral analyses

As a preparation step for mineral analysis, faecal andgrass samples were ashed through microwave destructionwith 10 ml HNO3 in closed vessels followed by filtration.Afterwards, the faecal and grass samples were analysed forZn, Cu, Fe and Mn concentrations through inductivelycoupled plasma optical emission spectrometry (ICP-OES)(Vista MPX radial, Varian, Palo Alto, USA) and for Co, Se, Iand S by means of inductively coupled plasma massspectrometry (ICP-MS) (Elan DRC-e, Perkin Elmer, Sunny-vale, USA). Plasma samples were prepared for mineralanalysis through microwave destruction with 10 ml HNO3

in open vessels followed by filtration and analysed for Cuand Zn concentrations through ICP-OES and Mn and Seconcentrations through ICP-MS.

Throughout mineral analyses, a quality control pro-gramme was in use. Sampled matrices were spiked withelements under study with two concentrations in therange of the measured concentrations and recoveries weremeasured. Average recovery was 94%, with a rangebetween 82% (Cu in faeces) and 113% (Se in plasma), whichshould probably be attributed to matrix interferences.Detection limits in acid digest were: Mn 0.35 μg/l, Cu0.25 μg/l, Mo 0.33 μg/l, Se 0.13 μg/l, Fe 21.4 μg/l, Zn16.4 μg/l, and Co 0.14 μg/l. Standards were regularly runbetween samples. Analytical results were blank-corrected.Prior to use, all glassware and microwave vessels wererinsed with diluted HNO3. Ultrapure HNO3 (analyticalgrade for trace elements) was used during all analyticalprocedures.

2.5. Proximate and fibre analysis and digestibilitycalculation

Faecal and grass samples were also analysed for drymatter (920.36), crude protein (984.13), crude ash (923.03)and crude fat (920.39) by means of proximate analysis

(AOAC, 2000). Additionally, acid detergent fibre (ADF) andacid detergent lignin (ADL) were analysed according toAOAC (2000); 973.18 and neutral detergent fibre (NDF) bya method of Van Soest et al. (1991). Apparent nutrientdigestibility as well as apparent mineral absorption werecalculated as following: ((Wdiet�Cdiet)−(Wfaeces�Cfaeces))/(Wdiet�Cdiet)�100 where W is the collected weight, C isthe nutrient concentration (both on dry matter basis), dietrefers to the offered diet including supplement aftersubtracting refusals, and faeces refers to the total faecaloutput.

2.6. Plasma enzyme and acyl carnitines analysis

Moreover, plasma was analysed for the mineral depen-dent enzymes ceruloplasmin (EC 1.16.3.1) with thep-phenylenediamine oxidase method (Sunderman andNomoto, 1970) and total superoxide dismutase (SOD) (EC15.1.1) by means of the inhibition of WST-1 to WST-1formazan reduction reaction (Peskin and Winterbourn,2000). The latter reaction measured total superoxidedismutase activity in plasma, according to earlier researchconsisting mainly of EC-SOD (SOD3) (EC 15.1.1), a Cu andZn-containing tetramer, and to a lesser degree of CuZnSOD (SOD1) (EC 15.1.1) and MnSOD (SOD2) (EC 15.1.1)as a result of leakage out of cells (Marklund, 1984). Finally,acyl carnitines analysis was performed through quantita-tive electrospray tandem mass spectrometry (Rizzo et al.,2003). The plasma acyl carnitine profile served as reflec-tion of the mitochondrial acetyl-CoA pool and thus, theavailable energy substrates for the citric acid cycle (Brassand Hoppel, 1980; Bremer, 1983).

2.7. Statistical analysis

All statistical analyses were performed using SPSS v17.0(SPSS Inc., Chicago, IL, USA). Missing data (1 value for faecalmineral concentrations and 1 value for plasma acyl carni-tines, ceruloplasmin and SOD) were replaced with the meanof the non-missing values of all individuals at the specifictime point (Gadbury et al., 2003). All data except feedcomposition were fit to a repeated measures model withtreatment, time and their interaction inserted as fixed effectsand baseline measurements (week 1) as covariate. Individualanimals served as experimental unit. Feed composition datawere analysed using one-way analysis of variance. Signifi-cance was declared at a probability level of Po0.05; Po0.1was interpreted to indicate a trend.

3. Results

Dietary concentrations of ash, fat, Cu, Zn and Mn differedsignificantly over the experimental period (Table 1). Mineralanalysis of the grasses indicated a suboptimal supply of Cu(o10mg/kg DM) and Se (o0.10 mg/kg DM) throughoutthe whole trial, while I was too low in week 2 and 3(o0.50 mg/kg DM), upon comparisonwith recommendationsfor Bos taurus beef cattle established by NRC (2000). Accordingto Suttle (2010), Fe is antagonistic towards Cu when the Fe:Curatio is exceeding 50 whereas S and Mo are significantlydepressing Cu absorption when S is higher than 2000 mg/kg

V. Dermauw et al. / Livestock Science 155 (2013) 255–261258

DM combined with a Cu:Mo ratio lower than 3. Diet analysisvalues of all three elements showed values above thesethresholds: for Fe constantly, for S and Mo in week 4,respectively.

At the onset of the study, three out of eight bulls hadplasma Cu concentrations below disorder risk values forB. taurus cattle according to Suttle (2010), whereas two forMn, and one for Zn. Supplementation of trace elementsresulted in increased plasma concentrations of Cu, Zn, Mnand Se (Table 2), even though mean baseline and esti-mated marginal means of plasma mineral concentrationswere above these risk values in both groups. Cu, Zn andMn plasma values were also affected by a time� supple-ment interaction (all P¼0.001) (data not shown inTable 2). Faecal concentrations of Cu, Zn, Se and Mn wereraised by trace element supplementation (all Po0.05),whereas faecal Co concentrations tended to be higher inthe supplemented group (P¼0.05), faecal I concentrations,as an exception within the supplemented minerals, werenot affected by the supplementation (P40.05). Mineralrelated ceruloplasmin and SOD activity remained unaf-fected by supplementation (Table 3). Mean baseline andestimated marginal means of ceruloplasmin activities in

Table 2Trace element supplementation effects on estimated marginal means of plasma

Parameter Baselinea Treatment

Controlb Supplemen

Plasma mineral, mg/lMn 0.031 0.053 0.297Zn 0.89 0.89 1.40Cu 0.61 0.61 0.82Se 0.070 0.059 0.070Faeces mineral, mg/kg DMMn 441 520 575Zn 127 138 196Cu 16 19 35I 1.0 1.3 1.7Se 0.13 0.21 0.36Co 2.0 1.4 1.6

SE¼Standard error, P¼P-value at significance level Po0.05.a Baseline¼mean baseline concentrations (n¼8) in week 1.b Estimated marginal means of the treatment group¼means per treatme

measurements in week 1 (inserted in the model as a covariate).c From Suttle (2010).d Reference value for serum, no reference value available for plasma.

Table 3Trace element supplementation effects on estimated marginal means of plasma

Parameter Baselinea

Enzyme activity Ceruloplasmin (U/l) 131Superoxide dismutase (U/ml) 6.1

SE¼Standard error, P¼P-value at significance level Po0.05.a Baseline¼mean baseline enzyme activity (n¼8) in week 1.b Estimated marginal means of the treatment group¼means per treatme

measurements in week 1 (inserted in the model as a covariate).

both treatment groups were substantially higher than thethreshold value for Cu deficiency of 15 U/l suggested forB. taurus cattle by Laven et al. (2007).

Trace element supplementation affected apparent digest-ibility neither of the proximate components nor of fibrefractions (P40.05) (Table 4). A time� supplementationinteraction affected apparent DM, crude protein and ADLdigestibility (all Po0.05) while apparent ash (P¼0.09) andNDF (P¼0.07) digestibility tended to be affected by thisinteraction. This interaction seemed to originate from amajor and consistent shift in effect size between the twogroups in week 3 of supplementation (data not shown inTable 4). Apparent Se and I absorption increased in thesupplemented group (both Po0.05). Apparent Mn and Iabsorption was affected by time� supplementation interac-tion (both Po0.05) and the same interaction tended to affectapparent Cu and Zn absorption (P¼0.07; P¼0.08, respec-tively) (data not shown in Table 4). No effect of supplemen-tation was observed on the plasma acyl carnitine profile, asan estimate of nutrient utilisation from enzymatic or fer-mentative origin (P40.05) (Table 5). Finally, trace elementsupplementation did not induce a difference in body weight(170 vs. 171 kg73, P¼0.875).

and faecal mineral concentrations in grass fed zebu (Bos indicus) bulls.

SE P Reference valuesc

tb

0.025 0.002 40.020d

0.08 0.006 40.600.03 0.004 40.600.002 0.017 40.020

14 0.027 –

7 0.001 –

2 0.001 –

0.1 0.156 –

0.02 0.004 –

0.1 0.050 –

nt over all repeated measures of week 2–5 adjusted for the baseline

mineral related enzyme activity in grass fed zebu (Bos indicus) bulls.

Treatment SE P

Controlb Supplementb

100 121 13 0.3815.8 5.6 0.7 0.875

nt over all repeated measures of week 2–5 adjusted for the baseline

V. Dermauw et al. / Livestock Science 155 (2013) 255–261 259

4. Discussion

In the current study, trace element supplementationsuccessfully raised plasma and faecal trace element con-centrations of zebu bulls fed a local grass diet. Thisincrease occurred despite natural variation in dietary traceelements, indicating a suboptimal supply for some ele-ments (Cu, Se, and I) while an adequate supply for others(Mn, Zn, and Co) upon comparison with B. taurus require-ments (NRC, 2000). Furthermore, plasma and faecal Cuconcentrations were increased despite the presence ofhigh concentrations of antagonists (Mo, S, and Fe), capableto form insoluble complexes with Cu in the rumen. Inexcess, thiomolybdate complexes (formed by Mo and S),can also bind Cu at post-absorption sites, additionallycausing a thiomolybdate toxicity (Gould and Kendall,2011).

Table 4Trace element supplementation effects on estimated marginal means ofapparent nutrient digestibility and apparent mineral absorption in grassfed zebu (Bos indicus) bulls.

Parameter Baselinea Treatment SE P

Controlb Supplementb

Apparentnutrientdigestibility(%)

DM 80 76 74 2 0.513Ash 62 61 58 3 0.577EE 84 70 69 1 0.461CP 84 79 77 2 0.401NDF 79 72 72 2 0.955ADF 77 69 68 2 0.780ADL 50 34 22 4 0.135

Apparentmineralabsorption (%)

Mn 20 46 41 3 0.412Zn 41 32 36 6 0.699Cu 40 35 49 6 0.320I 70 51 74 4 0.021Se −13 12 62 9 0.026Co 5 54 50 4 0.631

DM¼Dry matter, EE¼ether extract, CP¼crude protein, NDF¼neutraldetergent fibre, ADF¼acid detergent fibre, ADL¼acid detergent lignin,SE¼standard error, P¼P-value at significance level Po0.05. SE=standarderror, P=P-value at significance level Po0.05

a Baseline¼mean baseline apparent nutrient digestibility/apparentmineral absorption (n¼8) in week 1.

b Estimated marginal means of the treatment group¼means pertreatment over all repeated measures of week 2–5 adjusted for thebaseline measurements in week 1 (inserted in the model as a covariate).

Table 5Trace element supplementation effects on estimated marginal means of plasma

Parameter Baselinea

Acyl carnitines (μmol/l) Acetyl 6.9Propionyl 0.67Butyl 0.34Isovaleryl 0.093-OH-butyryl 0.053-OH-isovaleryl 0.07Methylmalonyl 0.05

SE=standard error, P¼P-value at significance level Po0.05a Baseline¼mean baseline concentrations (n¼8) in week 1.b Estimated marginal means of the treatment group¼means per treatme

measurements in week 1 (inserted in the model as a covariate).

Previous research indicated a Cu, Se and possibly Nadeficiency problem in grazing zebu cattle in the study area(Dermauw et al., 2013). In the current study, some animalshad initial plasma mineral concentrations indicating a risk fortrace element disorder according to Suttle (2010). Despitethis, mean baseline and estimated marginal concentrations inboth treatment groups were above these threshold values forB. taurus cattle. Insufficient research is available to determinewhether these values are also applicable to B. indicus cattle.Furthermore, despite the changed Cu and Zn plasma status inthe supplemented group, activities of Cu and Zn-relatedenzymes ceruloplasmin and SOD did not differ significantlybetween groups, in contrast to earlier data (ceruloplasmin:Legleiter and Spears, 2007; SOD: Cao and Chen, 1991;Shaheen and Abd El-fattah, 1995), and ceruloplasminactivity at the onset and throughout the trial was above thethreshold value suggested for B. taurus cattle by Laven et al.(2007). Consequently, although supplementation caused animproved status of the supplemented minerals, the status onitself was probably adequate for most bulls throughout thetrial according to B. taurus threshold values. As the dietprovided to the animals prior to purchase could have been ofadequate mineral quality, the latter could be explained by thecapacity of soft tissue storage for several minerals, e.g. in liverfor Cu, thyroid for I, kidney for Se (NRC, 2005). Mineralanalysis of several grass species in previous work around theregion of origin of the animals does contradict the hypothesisof a correct diet prior to the trial: of 22 grass samples, 22 hadcopper concentrations below requirements for beef cattle(NRC, 2000) (range: 1.7–9.3 mg/kg DM), 12 for Zn (5.5–59 mg/kg DM) and 18 for Se (10–380 μg/kg DM) (Dermauwet al., unpublished data). Another explanation for this phe-nomenon could be a difference between cattle species(B. indicus vs. B. taurus) in mineral metabolism resulting indifferent trace element requirements and normal plasmaranges. Earlier research detected such differences for plasmaCu concentrations within B. taurus (Mullis et al., 2003; Wardet al., 1995) as well as for Se (Rowntree et al., 2004),therefore, similar or even larger differences could existbetween these species as suggested by McDowell (1985).

Nevertheless, the main objective of the present study wasto detect early effects of trace element supplementation onnutrient digestibility and utilisation. In the present study, traceelement supplementation did not affect nutrient digestibility.The presence of the time� supplementation interaction for

acyl carnitines concentrations in grass fed zebu (Bos indicus) bulls.

Treatment SE P

Controlb Supplementb

5.5 5.3 0.3 0.6700.63 0.56 0.08 0.5660.27 0.27 0.02 0.9120.11 0.12 0.01 0.3250.03 0.04 0.01 0.1840.05 0.06 0.007 0.5570.03 0.04 0.004 0.776

nt over all repeated measures of week 2–5 adjusted for the baseline

V. Dermauw et al. / Livestock Science 155 (2013) 255–261260

apparent DM, crude protein and ADL digestibility and appar-ent Mn and I absorption, originating from the major shiftbetween the two groups inweek 3 of supplementation cannotbe attributed to a specific factor. However, the interactionbetween time and supplementation did not reflect a divergentdifference between the two groups. Overall, it can be con-cluded that trace element supplementation did not improveapparent nutrient digestibility nor apparent mineral absorp-tion in the present study, which is in accordance with thefindings of Grace et al. (2002) in horses. As an exception, theapparent absorption of Se and I was affected by supplementa-tion. Both elements seemed to be absorbed to a higher degreewith increasing dietary intake, which confirms the lack ofhomeostatically controlled absorption mechanisms in theseelements (Suttle, 2010). For minerals, apparent absorptionresults should be carefully interpreted, as they merely providean estimation of their bioavailability, since certain post-absorption processes and differences in excretion rates canresult in differences in bioavailability despite equal apparentabsorption rates (Ammerman et al., 1995).

Finally, plasma acyl carnitines were not influenced bytrace element supplementation. These circulating carnitineesters mirror the available citric acid cycle energy substratesand thus nutrient utilisation as described by Verbruggheet al. (2009). Isovaleryl-, 3-OH-butyryl-, 3-OH-isovaleryl- aswell as methylmalonylcarnitine are products of branched-chain amino acid catabolism (Michal, 1999) and represent therelative importance of amino acids as an energy source.Acetyl-, propionyl-, and butyrylcarnitine reflect the contribu-tion of energy from the respective volatile fatty acidsproduced in fermentation (Bremer, 1983). The lack of effectof trace element supplementation on the presented productssuggests that no alterations in energy metabolism wereinduced during the experimental period.

5. Conclusion

In the current study, concentrations of Mn, Zn, Cu and Sein plasma of grass-fed zebu (B. indicus) bulls were increasedby trace element supplementation (Mn, Zn, Cu, Se, Co and I),indicating an altered mineral status although mean treat-ment values were still within normal ranges for B. tauruscattle. The latter is in sharp contrast to subnormal dietary Seand Cu concentrations according to B. taurus guidelines andcould have implications for the applicability of B. taurusmineral requirements in B. indicus cattle. Ceruloplasmin andsuperoxide dismutase remained unaffected by supplementa-tion. Supplementation of trace elements did not induce adifference in nutrient digestibility and utilisation, although itdid affect apparent Se and I absorption.

Conflict of interest statement

The authors declare that they have no conflict ofinterest.

Acknowledgements

The present study was funded by the Agency for thePromotion of Innovation through the Science and

Technology in Flanders (IWT-Vlaanderen), Grant no.091348. We would like to acknowledge the IUC-JU pro-gramme of VLIR-UOS for logistical support, Ria Van Hulleand Joachim Neri for mineral analyses, Daniel Vermeulenfor ceruloplasmin and SOD analyses and Wout Dalemans,Thomas Van Hecke and all animal keepers of the JimmaUniversity College of Agriculture and Veterinary Medicinefor their assistance during the experimental period andanimal sampling.

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