Inorganic Versus Complexed Trace Mineral Supplements on Performance of Dairy Cows1

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The Professional Kincaid Animaland Scientist Socha 20 (2004):66–73

Versus Complexed Inorganic Trace Mineral Supplements on Performance of Dairy Cows1

R. L. KINCAID*,2 and M. T. SOCHA†, PAS, Dpl. ACAN *Animal Sciences Department, Washington State University, Pullman 99164 and †Zinpro Corporation, Edina Prairie, MN 55344

Abstract

for yield of milk, energy-corrected milk, and 3.5% FCM; the response to CTM To determine the effects of chemical was greatest from wk 5 through wk 10 form of trace mineral supplements on postpartum. Colostrum of cows fed the performance of dairy cows, Holstein cows CTM prepartum had greater IgG (n = 36) were assigned to dietary treat(P<0.05) and lesser Zn concentrations. ments of inorganic trace minerals or a There was no difference between treatcombination of inorganic and complexed ments in concentrations of IgM, Co, Mn, trace minerals (CTM). Starting at 21 d or Cu in colostrum. Although there were prepartum, dry cows were fed hay and a period effects on serum concentrations of grain supplement that contained one of IgG, IgM, nonesterified fatty acids the trace mineral supplements. Cows (NEFA), Zn, Co, and Ca, there were no continued to receive their respective trace treatment effects. These results indicate mineral treatment from parturition until that CTM may benefit cows at peak 150 d in milk (DIM). Cows fed the production. CTM lost less BW prepartum (P<0.05); however, there was no difference between (Key Words: Cows, Inorganic Trace treatments in postpartum BW change or Minerals, Complexed Trace Minerals, body condition score (BCS). The DMI of Supplements.) lactating cows were similar between treatments. Actual milk yield (42.2 vs 41.7 kg/d), 3.5% fat-corrected milk Nutritional deficiencies of Zn, Cu, (FCM) (42.3 vs 42.3 kg/d), and meaand Co reduce ADG and DMI of sures of production efficiency also were similar between treatments. There was a ruminants (McDowell, 1992). In a study to separate the effects of trace week × treatment interaction (P<0.05) element deficiencies on DMI and feed efficiency, Miller et al. (1965) used a restricted-fed control group to demonstrate that Zn deficiency per se 1Supported by Federal Hatch funds, the Collessened feed efficiency of calves. lege of Agriculture and Home Economics, Trace elements also can interact with Washington State University (Pullman), and other nutrients to produce associative Zinpro Corporation (Eden Prairie, MN). effects on animals. For example, 2To whom correspondence should be addietary protein restriction reduced Zn dressed: [email protected] absorption and retention in calves

Introduction

(Stake et al., 1973). Hatfield et al. (1995) obtained greater (P<0.10) feed intakes in gestating ewes fed either a Zn-Met supplement or a diet with increased CP (14.9%) compared with ewes fed a diet with lesser CP (11.3%) and no Zn-Met supplement. In addition, milk production was greater (P<0.10) at 28 d postpartum in ewes fed either the 14.9% CP diet or the Zn-Met supplement. When intakes of many trace elements are low, homeostatic control mechanisms increase the intestinal absorption efficiency for the trace element (Miller, 1975). For example, Neathery et al. (1973) reported that cows fed diets low in Zn (16.6 ppm) had a net absorption of Zn of 53% compared with 35% Zn absorption in cows fed diets with 39.5 ppm of Zn. Studies that have compared the intestinal absorption efficiency and tissue retention of inorganic and organic trace elements have reported both similar (Yost et al., 2002; Miltimore et al., 1978 ) and greater absorption of trace elements from organic compared vs inorganic forms (Stanton et al., 1998; Rabiansky et al., 1999) depending upon the presence of antagonists to absorption (Kincaid et al., 1986), use of growth implants (Huerta et al., 2002), and age of the cattle (Kincaid et al., 1997). Other factors that affect

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Trace Mineral Supplements for Dairy Cows

response to organic trace minerals may include the particular trace element, binding affinity between the trace element and chelating agent, and the dietary concentration of the trace element. Ballantine et al. (2002) reported increased milk yield in cows fed a combination of complexed trace minerals (CTM) and sulfate forms of trace minerals. However, an explanation of the biological basis for an increase in milk yield is unclear, and more work is needed. Thus, the objective of this study was to compare inorganic trace mineral supplements and supplements containing a combination of inorganic and organic trace minerals on feed intake, milk production, measures of milk production efficiency, and blood metabolites in lactating dairy cows.

Materials and Methods The protocol for this experiment was approved by the WSU Animal Care and Use Committee. Multiparous Holstein cows (n = 36) were randomly assigned to diets supplemented with either inorganic trace minerals or to diets supplemented with a combination of inorganic minerals and CTM (Cu, Zn, Mn, and Co). Cows were vaccinated with J-5® (E. coli; Pharmacia Animal Health, Exton, PA) and Triangle 4® (killed IBR, PI3, and BRSV; Pharmacia Animal Health). At 21 d before their expected calving date, cows were assigned to prepartum diets of grass hay provided free choice and were individually fed 3.3 kg/d (DM basis) of concentrate to provide treatment supplements of trace elements. The concentrate was composed of 82.3% ground corn, 10% soybean meal (44% CP), 4% molasses, 1.5% iodized salt, 1% trace mineral premix (Table 1), 0.5% limestone, 0.2% magnesium oxide, 0.1% vitamin D premix (8810 IU/g), 0.025% vitamin A premix (30,000 IU/g), 0.2% Se premix (200 mg/kg Se as Na selenite), 0.1% vitamin E premix (500 IU/g), and 0.05% pellet binder. Based upon chemical analysis of the hay and

TABLE 1. Trace mineral premixes for dry cow concentrates. Dietary treatment Item

Inorganica

Complexedb (% of salt mix)

Iodized salt 4-Plexc CoSO4d CuSO4.5H2Oe ZnSO4.H2Of MnSO4.H2Og

86.874 0.0 0.206 1.82 5.97 5.13

50.598 43.0 0.0 0.312 2.83 3.26

aThe

inorganic mineral premix was formulated to provide 25 mg/d of Co as Co sulfate, 150 mg/d of Cu as Cu sulfate pentahydrate, 700 mg/d of Zn as Zn sulfate monohydrate, and 550 mg/d of Mn as Mn sulfate monohydrate. bThe complexed mineral premix was formulated to provide 25 mg/d of Co as Co glucoheptonate, 25 mg/d of Cu as Cu sulfate pentahydrate, 125 mg/d of Cu as Cu lysine, 340 mg/d of Zn as Zn sulfate monohydrate, 360 mg/d of Zn as Zn Met, 350 mg/d of Mn as Mn sulfate monohydrate, and 200 mg/d of Mn as Mn Met. cContains 2.58% Zn as Zn Met, 1.43% Mn as Mn Met, 0.90% Cu as Cu Lys, and 0.18% Co as Co glucoheptonate. d33% Co as Co sulfate. e25% Cu as Cu sulfate pentahydrate. f35.5% Zn as Zn sulfate monohydrate (dried).

TABLE 2. Chemical composition of concentrates and hay fed to dry cows. Concentrate with treatment trace minerals Item CP, % NDF, % ADF, % Ash, % Ca, % P, % Co, mg/kg Zn, mg/kg Cu, mg/kg Mn, mg/kg Fe, mg/kg Se, mg/kg aAll

Inorganica 13.6 11.6 1.8 5.9 0.45 0.36 6.7 195 33 98 108 0.79

Complexedb 13.5 11.8 1.6 6.7 0.46 0.38 7.8 216 34 114 88 0.74

Hay 12.92 58.3 33.1 9.1 0.60 0.30 BDLc 22 4.4 35 218 BDL

supplemented trace minerals were inorganic forms. mineral supplements were a combination of inorganic and complexed trace minerals. cBDL = Below detection limit. bTrace

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TABLE 3. Composition of total mixed ration for lactating cows. Item (%, DM basis) Alfalfa silage Alfalfa hay Concentratea Wheat mill run Cottonseeds, whole

25.62 22.28 35.65 6.57 9.88

aThe ingredient composition of the concentrate was 42.175% corn, 30% barley, 7.89% peas, 4% corn gluten meal, 4.5% soybean mean (44% CP), 4.5% molasses, 2.5% sodium bicarbonate, 0.8% limestone, 0.8% dicalcium phosphate, 1.5% iodized salt, 0.6% trace mineral premix, 0.5% fat, 0.4% magnesium oxide, 0.2% Se premix (200 mg/kg of Se), 0.05% vitamin D premix (8810 IU/g), 0.025% vitamin A premix (30,000 IU/g), 0.01% vitamin E premix (500 IU/g), and 0.05% pellet binder.

concentrates (Table 2), the 3.3 kg/d of concentrate and an estimated hay intake of 9.1 kg/d provided daily prepartum intakes of 148 mg of Cu, 856 mg of Zn, 660 mg of Mn, and 23 mg of Co. Postpartum cows were fed a lactation total mixed ration (TMR)

formulated to provide a trace mineral supplement of either inorganic or a combination of inorganic and organic sources. The lactation TMR (Table 3) consisted of alfalfa hay and haylage, whole cottonseeds, wheat mill run, and concentrate. The ingredient composition of the trace

TABLE 4. Salt premixes for treatment concentrates for lactating cows. Item

Inorganica

87.05 0 0.18 1.82 5.82 5.13

TABLE 5. Chemical composition of total mixed ration fed to lactating cows. Item

Concentration

Complexedb (% of salt mix)

Iodized salt 4-Plexc CoSO4.7H2Od CuSO4e ZnSO4f MnSO4g

mineral premixes is provided in Table 4, and the chemical composition of the TMR is given in Table 5. Cows were individually fed via Calan head gates and were fed their dietary treatment until 150 d in milk (DIM). Daily DMI were recorded for lactating cows, and samples of the TMR were taken weekly and composited by month. Cow BW and BCS were taken monthly. Blood samples were collected into heparinized and non-heparinized vacutainers on d –21, 0, 28, and 150 relative to parturition. Immediately postpartum, a sample of colostrum was collected. Milk yields were recorded daily, and samples of a.m./p.m. milk were taken monthly for analysis of major components by the regional Dairy Herd Improvement Association (DHIA) laboratory (Burlington, WA). Samples of serum, whole blood, colostrum, and milk were frozen until analysis.

50.598 43.0 0 0.132 2.83 3.26

aThe inorganic mineral premix was formulated to provide 25 mg/d of Co as Co sulfate, 300 mg/d of Cu as Cu sulfate pentahydrate, 1400 mg/d of Zn as Zn sulfate monohydrate, and 1100 mg/d of Mn as Mn sulfate monohydrate. bThe complexed mineral premix was formulated to provide 25 mg/d of Co as Co glucoheptonate, 150 mg/d of Cu as Cu sulfate pentahydrate, 125 mg/d of Cu as Cu Lys, 1040 mg/d of Zn as Zn sulfate monohydrate, 360 mg/d of Zn as Zn Met, 900 mg/d of Mn as Mn sulfate monohydrate, and 200 mg/d of Mn as Mn Met. cContains 2.58% Zn as Zn Met, 1.43% Mn as Mn Met, 0.90% Cu as Cu Lys, and 0.18% Co as Co glucoheptonate. d33% Co as Co sulfate. e25% Cu as Cu sulfate pentahydrate. f35.5% Zn as Zn sulfate monohydrate. g32.5% Mn in Mn sulfate monohydrate.

(DM basis) NEL, Mcal/kg CP, % UIPa, % DIPb, % NDF, % ADF, % Ca, % P, % Mg, % Na, % K, % S, % Cl, % Co, ppm Cu, ppm I, ppm Mn, ppm Se, ppm Zn, ppm aUIP bDIP

1.65 19.6 4.7 11.0 31.4 21.0 1.00 0.455 0.37 0.33 1.6 0.26 0.63 1.7 20.0 0.74 67.0 0.33 75.0

= Undegradable intake protein. = Degradable intake protein.

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Trace Mineral Supplements for Dairy Cows

Composite feed samples were dried (60o C for 48 h), ground to pass a 2mm screen (Wiley mill; Arthur H. Thomas Co., Philadelphia, PA), subsampled, reground to pass through a 1-mm screen, and subsampled again. Feed analysis consisted of DM at 100o C (AOAC, 1990), CP by an automated N analyzer (Leco FP-528; Leco Corp., St. Joseph, MI), ether extract (AOAC, 1990), and NDF and ADF using an

Ankom 200 Fiber Analyzer (Ankom Technologies, Fairfield NY). Blood samples were analyzed for Co by neutron activation analysis (60Co with a half-life of 5.27 yr using a multichannel analyzer) at the Washington State University Nuclear Reactor Center (Pullman). Copper, Ca, Zn, Co, and Fe concentrations were determined by atomic absorption spectrophotometry (Robinson, 1975), K and Na by atomic emission

spectrophotometry (Robinson, 1975), Mn by graphite furnace atomic absorption spectrophotometry (CHGA-400; Perkin-Elmer, Norwalk, CT), and P by colorimetry (AOAC, 1990). Milk fat and protein composition were determined via infrared spectrophotometer (Bentley 2000; Bentley Instruments, Chaska, MN) at the regional DHIA laboratory (Burlington, WA). Nonesterified fatty acids (NEFA) were measured using a

TABLE 6. Effects of trace element source on intake of DM and NEL, BW, milk production, and measures production efficiency in lactating cows. Treatment (Trt) Item DMI, kg BW, kg Precalving BW change Postcalving BW change BCSc NEL intake, Mcal Milk yield, kg 3.5% FCMd, kg ECMe, kg Milk components SNFf % kg Protein % kg Fat % kg Production efficiency measures EBg FEh Energy efficiencyi

Inorganic

Complexed

Comparison SE

Trt

Wk

Trt × wk

26.0 685 –54.7 –20.9 3.08 42.9 42.2 42.3 41.3

26.4 710 –23.3 –48.0 3.12 43.6 41.7 42.3 41.6

0.92 12.4 10.2 13.3 0.05 1.48 1.4 1.3 1.4

NSa NS 0.04 NS NS NS NS NS NS

0.001 0.001 NAb 0.001 0.001 0.001 0.001 0.001 0.001

0.07 NS NA NS NS 0.06 0.001 0.001 0.001

8.5 3.61

8.8 3.71

0.06 0.12

0.02 NS

0.05 0.001

NS 0.001

2.74 1.16

2.87 1.19

0.04 0.04

0.04 NS

0.001 0.001

NS 0.001

3.51 1.48

3.61 1.49

0.09 0.05

NS NS

0.006 0.001

NS 0.001

3.7 1.91 0.76

5.2 1.74 0.70

1.2 0.1 0.04

NS NS NS

0.001 0.001 0.001

NS NS NS

aP>0.10. bNA

= Not applicable. = Body condition score (1 to 5; NRC, 2001). dFCM = Fat-corrected milk. eECM = Energy-corrected milk = (7.2 × kg of protein/d) + 12.92 × kg of fat/d) + 0.327 × kg of milk/d) based upon 3.5% milk fat and 3.2% milk protein according to Pires et al. (1997). fSNF = Solids-not-fat. gEB = Energy balance = NE – maintenance energy – milk energy. Maintenance energy = 0.08 × BW0.75. L hFE = Feed efficiency = FCM/DMI. iEnergy efficiency = [0.09(% fat) + 0.0547(% CP) + 0.192] × kg of milk/NE . L cBCS

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(i = 1 or 2), bj = effect of sampling at week j (j = 1 to 21), (ab)ij = interaction effect between treatment and sampling week, dl(aibj) = random effect of cow, and eijk = residual error term. The mature equivalent for milk yield of the previous lactation was used as the covariant in analysis of the production data. Significant treatment effects were declared at P<0.05, and trends for treatment effect were declared at P>0.05 and P<0.15.

Figure 1. Effect of trace element source on DMI of total mixed rations.

Results and Discussion commercial kit (NEFA-C; Wako Chemical GmbH, Neuss, Germany). Concentrations of IgG and IgM in serum and colostrum were measured by radial immunodiffusion (VMRD Inc., Pullman, WA). Statistics. Data were analyzed by the general linear model of PROC MIXED procedures for a completely randomized design with repeated measures (SAS, 2001). The cows were blocked by parity according to expected calving date, and treatment assignments were rotated among cows within a block. The analysis of all time series data was performed using the model Yijl = m + ai + bj + (ab)ij + dl(aibj) + eijl, where Yijl = dependent variable, m = dependent variable mean, ai = effect of treatment

Dry matter intakes of lactating cows were similar between treatments (Table 6) and increased in a typical fashion during the 150 DIM of the study (Figure 1). There was a tendency (P<0.07) for an interaction between treatment and week for DMI. Cows fed CTM had less DMI on wk 5 postpartum and greater DMI on wk 6, 7, 8, 9, and 11 postpartum (Figure 1). For the lactating cows, average daily intakes (mg/d) of trace elements, calculated from the DMI and concentrations in the TMR, were 1900 mg/d of Zn, 2300 mg/d of Mn, 498 mg/d of Cu, and 51 mg/d of Co. Cows fed the CTM lost less (P<0.05) BW prepartum than did cows fed inorganic trace elements; however, there were no treatment

differences in BW change during the lactation period (Figure 2; Table 6). This result agrees with the conclusions of Hatfield et al. (1995) who reported greater DMI during gestation of ewes fed Zn-Met. Body condition scores (BCS) also were similar between treatments (Table 6). Changes in BW and BCS were typical for lactating cows in early lactation. Serum NEFA concentrations at 7 d postpartum were similar between treatments (Table 7). Additionally, reproductive measures that can be affected by BW changes such as days at first breeding (71 vs 69) days open (108 vs 104), services per conception (2.8 vs 2.6), and percentage pregnant by 150 d postpartum (54 vs 72) for inorganic and CTM, respectively, were similar. Actual, 3.5 fat-corrected milk (FCM) and energy-corrected milk yields were similar between treatments (Table 6; Figures 3 and 4). Cows fed the CTM had a greater (P<0.05) percentage of solids-not-fat (SNF) and a greater percentage of protein in milk, although yields of milk SNF and protein were similar between treatments. Milk fat percentage, yield, and somatic cell counts also were similar between treatments (Table 6). Several measures of milk efficiency were calculated using feed intake, milk produc-

TABLE 7. Effect of trace element source on measures in blood of cows. Treatment (Trt) Item Whole blood Mn, ppm Serum NEFA, mEq/dL Cu, ppm Co, ppm Zn, ppm Ca, mg/dL aP>0.10.

Comparison

Inorganic

Complexed

SE

Trt

Wk

Trt × wk

0.29

0.31

0.025

NSa

NS

NS

0.273 0.51 0.127 0.75 8.98

0.252 0.46 0.127 0.76 9.37

0.028 0.026 0.005 0.03 0.17

NS NS NS NS NS

0.001 NS 0.001 0.01 0.001

NS NS NS NS NS

Trace Mineral Supplements for Dairy Cows

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Figure 5. Effect of trace element source on protein yield.

Figure 2. Effect of trace mineral source on BW of cows.

Figure 3. Effect of trace element source on 3.5% fat-corrected milk (FCM) yield.

tion, and BW data. None of these measures (energy balance, feed efficiency, and energy efficiency) was affected by treatment (Table 6). There were time × treatment interactions (P<0.05) for yields of milk, 3.5% FCM, energy-corrected milk, SNF, milk protein, and milk fat (Figures 3, 4, 5, 6, and 7). In general, cows fed CTM produced more milk and milk components at peak production and less milk and milk components in midlactation. Ballantine et al. (2002) observed a time × treatment response to CTM for production of milk and milk components. Response to CTM was greatest at peak production and during the mid to late lactation period. It is difficult to explain why cows in the Ballantine et al. (2002) study responded to CTM during the mid to late lactation period other than cows were more stressed because of heat as this period corresponded to late summer. The concentrations of Cu, Zn, Co, and Ca in serum and Mn in whole blood were similar between treatments, although the concentrations of Co, Ca, and Zn changed with time during the experiment (Table 7). Similar to a previous report (Kincaid et al., 2003), serum Co declined in all cows during lactation (Figure 8). Concentrations of Co, Se, Mn, and Cu in colostrum were similar between treatments; however, the concentration of Zn was less in the

colostrum of cows fed the CTM (Table 8). Concentrations of IgG and IgM in serum and colostrum were measured as indicators of immune function. Whereas IgM was similar in the colostrum of cows (Table 8), IgG was increased (P<0.05) in cows fed the CTM. There was no treatment effect on concentration of IgG in serum; however, there was a tendency (P<0.11) for cows fed the CTM to have greater IgM (Table 8). Immunity is frequently reported to be affected by source of trace minerals, and increased immune function has been reported in cattle fed organic trace minerals forms (Stanton et al., 1998; Chirase and Greene, 2001).

However, some studies have reported either no difference (Kincaid et al., 1997; Spears and Kegley, 2002) or lessened immune function (Huerta et al., 2002). The mechanism whereby the chemical form of dietary trace minerals affects immunity is unknown; however, relative trace element availability within cells may be a factor. Differences between Zn metabolism in ruminants fed Zn as Zn-Met and inorganic Zn have been reported (Spears, 1989) with greater retention of Zn in liver of young calves fed Zn-Met than Zn oxide (Kincaid et al., 1997) but similar Zn retention in the liver of feedlot cattle fed Zn-Met and Zn sulfate (Huerta et al., 2002). Similarly, when heifers

Figure 4. Effect of trace element source on energy-corrected milk (ECM) yield.

Figure 6. Effect of trace element source on fat yield.

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Implications

Figure 7. Effect of trace element source on yield of solids-not-fat (SNF).

were fed hay containing a 1:5 ratio of Cu to Mo, there was greater tissue Cu retention for organic Cu than for Cu sulfate (Kincaid et al., 1986). In contrast, no difference in Cu repletion was observed when Cu-deficient heifers were fed organic Cu or Cu sulfate (Yost et al., 2002). In conclusion, overall milk yield and production efficiency were similar in cows fed either inorganic

Figure. Changes in serum Co from 21 d prepartum until 150 d in milk.

or a combination of inorganic and CTM. However, at peak lactation, cows appeared to benefit from CTM supplementation, as indicated by increased production of milk and milk components. Cows fed the CTM lost less BW prepartum, had greater IgG in colostrum, and had a tendency for greater IgM in serum than cows fed inorganic trace elements.

Although overall production efficiencies were similar between treatments in this study, the chemical form of trace elements affected specific physiological responses to supplementation. A better understanding is needed of how chemical form affects binding of trace elements to absorption antagonists. Similarly, more work is needed on the dissociation within the body of trace elements from their organic complex. Clearly, some differences exist in metabolism of inorganic and CTM, and, in some situations, these differences affect immunity and animal performance. These differences in metabolism between inorganic and CTM need to be understood to enable the formulation of diets that will maximize productive responses to trace element supplementation under various physiological and environmental conditions.

TABLE 8. Effects of trace element source on concentrations of immunoglobulins (IgG and IgM) and trace elements in colostrum and IgG and IgM in serum. Treatment (Trt) Item

Inorganic

Colostrum DM, % IgG, mg/dL IgM, mg/dL Co, ppm (wet) Se, ppm (wet) Mn, ppm (dry) Zn, ppm (dry) Cu, ppm (dry) Serum IgG, mg/dL IgM, mg/dL aP>0.10. bNA

= Not applicable.

Complexed

Comparison SE

Trt

Wk

Trt × wk

21.0 5118 752 0.060 0.059 0.45 125 3.90

23.3 7559 709 0.063 0.064 0.57 91 3.22

1.83 800 47 0.003 0.015 0.09 7.7 0.75

NSa 0.039 NS NS NS NS 0.004 NS

NAb NA NA NA NA NA NA NA

NA NA NA NA NA NA NA NA

3058 280

2862 350

240 29

NS 0.11

0.005 0.03

NS NS

Trace Mineral Supplements for Dairy Cows

Kincaid, R. L., R. M. Blauwiekel, and J. D. Cronrath. 1986. Supplementation of copper as copper sulfate or copper proteinate for growing calves fed forages containing molybdenum. J. Dairy Sci. 69:160.

Literature Cited Association of Official Analytical Chemists. 1990. Official Methods of Analysis. (Vol. 1. 15th Ed.). AOAC, Arlington, VA. Ballantine, H. T., M. T. Socha, D. J. Tomlinson, A. B. Johnson, A. S. Fielding, J. K. Shearer, and S. R. Van Amstel. 2002. Effects of feeding complexed zinc, manganese, copper, and cobalt to late gestation and lactating dairy cows on claw integrity, reproduction, and lactation performance. Prof. Anim. Sci. 18:211. Chirase, N. K., and L. W. Greene. 2001. Dietary zinc and manganese sources administered from the fetal stage onwards affect immune response of transit stressed and virus infected offspring steer calves. Anim. Feed Sci. Technol. 93:217. Hatfield, P. D., G. D. Snowder, W. A. Head, Jr., H. A. Glimp, R. H. Stobart, and T. Besser. 1995. Production by ewes rearing single or twin lambs: effects of dietary crude protein percentage and supplemental zinc methionine. J. Anim. Sci. 73:1227. Huerta, M., R. L. Kincaid, J. D. Cronrath, J. Busboom, A. B. Johnson, and C. K. Swenson. 2002. Interaction of dietary zinc and growth implants on weight gain, carcass traits and zinc in tissues of growing beef steers and heifers. Anim. Feed Sci. Technol. 95:15.

Kincaid, R. L., B. P. Chew, and J. D. Cronrath. 1997. Zinc oxide and amino acids as sources of dietary zinc for calves: effects on uptake and immunity. J. Dairy Sci. 80:1381. Kincaid, R. L., L. E. Lefebvre, J. D. Cronrath, M. T. Socha, and A. B. Johnson. 2003. Effect of dietary cobalt supplementation on cobalt metabolism and performance of dairy cattle. J. Dairy Sci. 86:1405. McDowell, L. R. 1992. Minerals in Animals and Human Nutrition. Academic Press, Inc., New York. Miller, W. J. 1975. New concepts and developments in metabolism and homeostasis of inorganic elements in dairy cattle. A review. J. Dairy Sci. 58:1549. Miller, W. J., W. J. Pitts, C. M. Clifton, and J. D. Morton. 1965. Effects of zinc deficiency per se on feed efficiency, serum alkaline phosphatase, zinc in skin, behaviour, graying, and other measurements in the Holstein calf. J. Dairy. Sci. 48:1329. Miltimore, J. E., C. M. Kalnin, and J. B. Clapp. 1978. Copper storage in the livers of cattle supplemented with injected copper and with copper sulfate and chelated copper. Can. J. Anim. Sci. 58:525. Neathery, M. W., W. J. Miller, D. M. Blackmon, and R. P. Gentry. 1973. Zinc-65 metabolism, secretion into milk, and biological half-life in lactating cows. J. Dairy Sci. 56:1526. Pires, A. V., M. L. Eastridge, J. L. Firkins, and Y. C. Lin. 1997. Effects of treatment and physical

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processing of cottonseed on nutrient digestibility and production performance by lactating cows. J. Dairy Sci. 80:1685. Rabiansky, P. A., L. R. McDowell, J. VelasquezPereira, N. S. Wilkinson, S. S. Percival, F. G. Martin, D. B. Bates, A. B. Johnson, T. R. Batra, and E. Salgado-Madriz. 1999. Evaluating copper lysine and copper sulfate sources for heifers. J. Dairy Sci. 82:2642. Robinson, J. W. 1975. Atomic Absorption Spectroscopy. (2nd Ed.). Marcel Dekker, Inc., New York, NY. SAS. 2001. SAS User’s Guide. (Version 8.1, 1st Ed.). SAS Inst., Inc., Cary, NC. Spears, J. W. 1989. Zinc methionine for ruminants: relative bioavailability of zinc in lambs and effects of growth and performance of growing heifers. J. Anim. Sci. 67:835. Spears, J. W., and E. B. Kegley. 2002. Effect of zinc source (zinc oxide vs zinc proteinate) and level of performance, carcass characteristics, and immune response of growing and finishing steers. J. Anim. Sci. 80:2747. Stake, P. E., W. J. Miller, and R. P. Gentry. 1973. Zinc metabolism and homeostasis in ruminants as affected by dietary energy intake and growth rate. Proc. Soc. Exp. Biol. Med. 142:494. Stanton, T. L., C. V. Kimberling, and A. B. Johnson. 1998. Effect of pre- and postshipment trace mineral type and level on subsequent feedyard performance and immune function. Prof. Anim. Sci. 14:225. Yost, G. P., J. D. Arthington, L. R. McDowell, F. G. Martin, N. S. Wilkinson, and C. K. Swenson. 2002. Effect of copper source and level on the rate and extent of copper repletion in Holstein heifers. J. Dairy Sci. 85:3297.