Department of Animal Science and Interdepartmental Nutrition Program, North Carolina State University, Raleigh

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1 Effect of zinc source (zinc oxide vs zinc proteinate) and level on performance, carcass characteristics, and immune response of growing and finishing steers 1,2 J. W. Spears 3 and E. B. Kegley 4 Department of Animal Science and Interdepartmental Nutrition Program, North Carolina State University, Raleigh ABSTRACT: Sixty Angus and Angus Hereford steers (246 kg initial BW) were used to determine the effects of Zn level and source on performance, immune response, and carcass characteristics of growing and finishing steers. s consisted of 1) control (no supplemental Zn), 2) ZnO, 3) Zn proteinate-a (ZnProt- A, 10% Zn), and 4) ZnProt-B (15% Zn). s 2, 3, and 4 supplied 25 mg of supplemental Zn/kg diet. Steers were individually fed a corn silage-based diet during the 84-d growing phase and a high corn diet during the finishing phase. Cell-mediated and humoral immune response measurements were obtained between d 67 and 74 of the growing phase. Equal number of steers per treatment were slaughtered after receiving the finishing diets for 84 or 112 d. Performance and carcass measurements were similar in steers fed the two ZnProt sources. Zinc supplementation, regardless of source, increased (P < 0.05) ADG during the growing phase. In the finishing phase, ADG (P = 0.10) and gain/ feed (P = 0.07) tended to be higher for steers fed ZnProt compared with those supplemented with ZnO. Gain and feed efficiency were similar for control and ZnO-supplemented steers during the finishing phase. Steers fed ZnProt had heavier (P < 0.05) hot carcass weights and slightly higher (P < 0.05) dressing percentages than those in the control or ZnO treatments. Quality grade, yield grade, marbling, and backfat were increased by Zn supplementation, but were not affected by Zn source. In vitro response of lymphocytes to mitogen stimulation and in vivo swelling response following intradermal injection of phytohemagglutinin were not affected by Zn level or source. Humoral immune response following vaccination with infectious bovine rhinotracheitis also was not affected by treatment. Soluble concentrations of Zn in ruminal fluid were higher (P < 0.05) in steers fed ZnProt compared to ZnO steers. Results indicate that ZnProt may improve performance of finishing steers above that observed with inorganic Zn supplementation. Key Words: Carcass Quality, Immune Response, Steers, Zinc 2002 American Society of Animal Science. All rights reserved. J. Anim. Sci : Introduction A number of different classes of organic trace minerals are commercially available for use in ruminant diets (Spears, 1996). Metal proteinates are defined as products resulting from the chelation of a soluble salt with amino acids and(or) partially hydrolyzed protein (AAFCO, 2000). Lambs supplemented with zinc pro- 1 Use of trade names in this publication does not imply endorsement by the North Carolina Agric. Res. Serv. or criticism of similar products not mentioned. 2 Supported in part by a gift from Chelated Minerals Corporation, Salt Lake City, UT. 3 Correspondence: phone: 919/ ; fax: 919/ ; Jerry_Spears@ncsu.edu. 4 Present address: Dept. of Animal Sci., University of Arkansas, Fayetteville, AR Received January 31, Accepted May 30, teinate (ZnProt) had a higher Zn retention than lambs given a similar concentration of Zn from inorganic ZnO (Lardy et al., 1992). Supplementation of lamb diets with ZnProt at high dietary concentrations (1,400 mg Zn/kg DM) resulted in greater tissue concentrations of Zn than for those supplemented with ZnSO 4 (Cao et al., 2000). In lactating dairy cows, replacing 50% of the supplemental Zn from ZnO with ZnProt resulted in fewer new mammary gland infections based on changes in somatic cell counts and bacteriological culture of milk samples (Spain, 1993). Control studies have not been conducted comparing ZnProt to inorganic Zn in growing and finishing cattle. Severe Zn deficiency is known to cause immunosuppression (Chesters, 1997). However, the effect of marginal dietary Zn on immune response of cattle has received little attention. We hypothesized that marginal dietary Zn would impair immune response and that ZnProt would be more bioavailable than inorganic ZnO. Therefore, the present study was conducted to deter- 2747

2 2748 Spears and Kegley Table 1. Ingredient and chemical composition of basal growing and finishing diets Item Growing Finishing Ingredient, % DM Corn silage 90.0 Ground corn Soybean meal Cottonseed hulls 5.00 Urea Calcium carbonate Potassium carbonate 0.50 Salt Vitamins A, D, and E a Trace minerals b + + Monensin c + Chemical composition DM, % CP, % Ca, % P, % Zn, mg/kg Cu, mg/kg Fe, mg/kg a Contained per kg of premix: vitamin A, 9,900,000 IU; vitamin D 3, 3,300,000 IU; and vitamin E, 3,300 IU. b Supplied in mg/kg diet: MnO, 31.3; CuSO 4, 31.7; Na 2 SeO 3, 0.22; CoCO 3, 0.087; and CaI 2 O 6, c Added to supply 22 mg/kg diet. mine the effects of dietary Zn level and source on performance, immune response, and carcass characteristics of growing and finishing cattle. Materials and Methods Care, handling, and sampling of the animals used in this study were approved by the North Carolina State University Institutional Animal Care and Use Committee (#92-165). Sixty Angus and Angus Hereford steers, averaging 246 kg initially, were blocked by weight and randomly assigned to treatments. s consisted of 1) control (no supplemental Zn), 2) ZnO, 3) ZnProt-A (Chelated Minerals Corp., Salt Lake City, UT), and 4) ZnProt-B (Chelated Minerals Corp.). s 2, 3, and 4 supplied 25 mg of supplemental Zn/ kg DM. The two ZnProt sources differed slightly with ZnProt-A containing 10% Zn and ZnProt-B containing 15% Zn. Steers remained on the same dietary treatments throughout both the growing and finishing phases. Steers were housed in groups of 12 in covered, slottedfloor pens and individually fed using electronically controlled feeders (American Calan, Northwood, NH). During the 84-d growing phase, steers were fed a corn silage-based diet supplemented with protein, minerals, and vitamins (Table 1). Zinc content of the control diet for the growing phase was 33 mg/kg diet DM. At the end of the growing phase, steers were gradually switched to a high concentrate finishing diet (Table 1). The control finishing diet analyzed 26 mg Zn/kg DM. Growing and finishing diets were formulated to meet or exceed all nutrient requirements for medium-framed steers with the exception of Zn (NRC, 1984). Diets were fed once daily in the morning in amounts adequate to allow ad libitum access to feed. Thirty-six steers were slaughtered after being fed the finishing diet for 84 d. The remaining 24 steers were slaughtered after being fed the finishing diet for 112 d. Steers were slaughtered at a commercial abattoir and hot carcass weights were obtained the day of harvest. Other carcass measurements were taken 48 h after slaughter by a USDA grader. Body weights were obtained prior to feeding on two consecutive days at the beginning and end of both the growing and finishing phases. Interim weights were taken at 28 d intervals prior to feeding. Blood samples were collected via jugular venipuncture and ruminal samples were obtained by stomach tube from 10 steers per treatment on d 56 of both the growing and finishing phases. Samples were collected at 2 h postfeeding. Ruminal fluid was centrifuged at 28,000 g for 30 min, and the supernatant used for ruminal soluble Zn determination. Blood was collected in heparinized vacuum tubes designed for trace mineral analysis (Becton Dickenson, Rutherford, NJ), and plasma obtained following centrifugation was analyzed for Zn. Zinc was measured by atomic absorption spectroscopy (Model 5000, Perkin- Elmer, Norwalk, CT). Feed samples were prepared for Zn analysis by wet ashing using nitric acid and hydrogen peroxide in a microwave digester (Model MDS-81D, CEM, Matthews, NC) as described by Gengelbach et al. (1994). The impact of dietary Zn on immunity was assessed toward the end of the growing phase. Cell mediated immune response was measured in vitro using a mitogen-induced lymphocyte blastogenesis assay described by Droke and Spears (1993). On d 67 of the growing phase, lymphocytes were isolated from peripheral blood of eight steers per treatment. Isolated lymphocytes were incubated for 72 h, and blastogenesis was determined by measuring incorporation of [ 3 H] thymidine (ICN Radiochemicals, Lisle, IL) into lymphocytes during the final 18 h of incubation. Phytohemagglutinin (PHA) and pokeweed mitogen (PWM) were used as mitogens in the blastogenesis assay at two different concentrations. Concentrations (PHA, 12.5 and 50 g/ ml; PWM, 10 and 40 g/ml) of mitogen used were based on previous research in our laboratory (Ward et al., 1993). The humoral immune response was assessed by measuring specific antibody production following vaccination of steers on d 70 for infectious bovine rhinotracheitis (IBR) using a modified live vaccine (Fermenta Animal Health, Omaha, NE). Blood samples were obtained before and 14 and 28 d after vaccination for determination of serum antibody titers. Neutralizing antibody titers against IBR were measured as described previously (Spears et al., 1991) and were expressed as log 2 of the highest dilution of serum causing neutralization of virus.

3 Zinc source and carcass traits in cattle 2749 Table 2. Effect of zinc level and source on performance of steers Item Control ZnO ZnProt-A ZnProt-B SEM Growing phase ADG, kg a DMI, kg Gain:feed Finishing phase ADG, kg b DMI, kg Gain:feed c Overall Initial wt, kg Final wt, kg ADG, kg DMI, kg Gain:feed a Control vs Zn treatments (P < 0.05). b ZnO vs ZnProt treatments (P = 0.10). c ZnO vs ZnProt treatments (P < 0.07). Cell-mediated immune response was also measured in vivo using an intradermal skin test and measuring skinfold thickness at the injection site. Six steers per treatment were injected intradermally with 150 g of PHA in 0.1 ml of phosphate-buffered saline, ph 7.4, on d 74 of the growing phase. The injection site (immediately posterior to the scapula) was shaved with surgical slippers and skinfold thickness was measured at 0, 2, 4, 6, 8, 12, and 24 h after injection using micrometric calipers. Data were statistically analyzed as a randomized complete block design using the GLM procedure of SAS (SAS Inst. Inc., Cary, NC). Antibody titers and skinfold thickness response to PHA injection were analyzed as repeated measures with animal within treatment as the error term for treatment effects. Differences between treatments were determined using single degree of freedom comparisons. Comparisons made were 1) control vs Zn treatment, 2) ZnO vs ZnProt treatments, and 3) ZnProt-A vs ZnProt-B. Significance was declared at P < 0.10 unless otherwise indicated. Results and Discussion Zinc supplementation, regardless of Zn source, increased (P < 0.05) ADG during the 84-d growing phase (Table 2). No differences were noted in ADG among Zn sources. Feed intake and gain:feed were not significantly affected by Zn source or level during the growing phase. Performance responses to Zn supplementation of growing cattle diets have been variable. In a series of studies with growing steers, Zn addition to basal diets containing approximately 20 mg Zn/kg DM improved ADG in only one of seven experiments (Beeson et al., 1977). The addition of 25 mg Zn/kg DM to a corn silage-based diet containing 24 mg Zn/kg DM increased ADG and feed efficiency in growing heifers during the first 56 d of a 126-d study (Spears, 1989). However, Zn supplementation did not affect heifer performance after the initial 56 d in that study. In the finishing phase, ADG tended (P = 0.10) to be higher and gain:feed tended to be greater (P = 0.07) for steers in the ZnProt treatments compared to those Table 3. Effect of zinc level and source on carcass characteristics of steers Item Control ZnO ZnProt-A ZnProt-B SEM Hot carcass wt, kg a Dressing percentage a,b Quality grade c,d Yield grade b Marbling c,e Ribeye area, cm 2a KPH, % Backfat thickness, cm b a ZnO vs ZnProt treatments (P < 0.05). b Control vs Zn treatments (P < 0.10). c Control vs Zn treatments (P < 0.05). d Select + = 16; Choice = 17; Choice 0 = 18. e Slight = 4; Small = 5; Modest = 6.

4 2750 Spears and Kegley Table 4. Effect of zinc level and source on plasma and ruminal soluble zinc concentrations Item Control ZnO ZnProt-A ZnProt-B SEM Growing phase Plasma Zn, mg/l Ruminal soluble Zn, mg/l a,b,c Finishing phase Plasma Zn, mg/l Ruminal soluble Zn, mg/l b,d a Control vs Zn treatments (P < 0.05). b ZnO vs ZnProt treatments (P < 0.05). c ZnProt-A vs ZnProt-B (P < 0.10). d Control vs Zn treatments (P < 0.10). supplemented with ZnO (Table 2). Performance of control steers did not differ from Zn-supplemented steers during the finishing phase. Perry et al. (1968) reported that Zn addition to finishing diets, containing 18 to 29 mg Zn/kg DM, improved ADG of steers in two of four experiments. In more recent studies, Zn supplementation of finishing diets containing 24 ppm Zn (Pond and Oltjen, 1988) or 30 mg Zn/kg DM (Nunnery et al., 1996) did not improve gain or efficiency of steers. In finishing studies in which the negative control diet was well above NRC (1996) recommended Zn requirements (due to Zn being included in the mineral premix) increasing dietary Zn also did not improve gain or feed efficiency (Greene et al., 1988, 1995; Malcolm-Callis et al., 2000). Gain, DMI, and gain:feed were similar for control and ZnO-supplemented steers over the entire growing and finishing period (Table 2). Overall steer performance was not significantly affected by Zn source; however, steers supplemented with ZnProt tended to gain more efficiently (P = 0.11) than those supplemented with ZnO. Steer performance did not differ between the two different ZnProt sources evaluated. Steers fed ZnProt-A or ZnProt-B had hot carcass weights 14 and 16 kg heavier (P < 0.05), respectively, than those in the ZnO treatment (Table 3). Hot carcass weights of control and ZnO-supplemented steers were similar. The heavier carcass weights in steers fed ZnProt compared to those fed ZnO resulted from a tendency for higher gain and also a slightly higher (P < 0.05) dressing percentage. Ribeye area was lower (P < 0.05) in steers fed ZnO compared to those fed ZnProt. The increased ribeye areas in steers fed ZnProt may be partly explained by the greater carcass weights in the ZnProt treatments. It is unclear why steers fed ZnProt tended to gain faster and have heavier carcass weights than steers fed a similar quantity of Zn from ZnO. Cao et al. (2000) recently reported that bioavailability of Zn from a ZnProt was higher than reagent grade ZnSO 4, based on increases in tissue Zn concentrations when supplemented to lamb diets at high concentrations (1,400 mg/ kg DM). However, if the carcass weight response in steers fed ZnProt was simply due to increased bioavailability of Zn, some improvement in carcass weights from ZnO relative to controls would be expected. Zinc oxide supplementation during the growing phase, when Zn appeared to limit growth in control steers, increased gain indicating that ZnO was providing available Zn. Results of the present study support the concept that organic Zn may be metabolized differently from inorganic Zn and, thus, may alter some metabolic processes differently (Spears, 1996). Zinc supplementation, regardless of source, increased quality grade and marbling (P < 0.05), and tended to increase yield grade and backfat thickness (P < 0.10), compared with non-zn supplemented steers. These results indicate that supplementation of physiological concentrations of inorganic zinc can alter quality and yield grades of steers in the absence of improved performance during the finishing phase. Zinc requirements are not well defined and little is known regarding factors that may influence zinc requirements of cattle (NRC, 1996). However, the control diet used in the present study was slightly below the NRC (1996) recommended Zn requirement (26 vs 30 mg Zn/kg DM). In most previous studies (Greene et al., 1988; Galyean et al., 1995; Malcolm-Callis et al., 2000), evaluating the effects of Zn on carcass characteristics, supplemental Zn treatments were compared to a control diet that already contained zinc added in the mineral premix. Control diets used in these earlier studies were much higher in Zn than the control diet in the current study. This likely explains the greater response in carcass characteristics especially to inorganic Zn supplementation in the present study. Greene et al. (1988) compared carcass characteristics of control steers fed a diet containing 82 mg Zn/kg DM to steers supplemented with an additional 360 mg Zn/d from either ZnO or Zn methionine. Zinc oxide did not affect carcass traits, but Zn methionine increased fat thickness, percentage of kidney, pelvic and heart fat, and quality grade compared to control and ZnO-supplemented steers (Greene et al., 1988). Addition of 20, 100, or 200 mg Zn/kg DM from ZnSO 4 to a finishing diet containing 70 mg Zn/kg DM resulted in a quadratic increase in fat thickness and yield grade with values being highest for steers receiv-

5 Zinc source and carcass traits in cattle 2751 Table 5. Effect of zinc level and source on serum antibody titers to IBR following vaccination a Time b Control ZnO ZnProt-A ZnProt-B SEM Day Day a Serum neutralizing antibody titers are expressed as log 2 of highest dilution of serum causing neutralization of virus. b Days after vaccination. ing 100 mg added Zn/kg DM (Malcolm-Callis et al., 2000). In contrast, supplementation of 35 or 70 mg Zn/ kg DM to diets that already had 30 mg of Zn added per kg DM did not affect carcass characteristics (Galyean et al., 1995). Plasma Zn concentrations were not affected by Zn level or source during the growing or finishing phase (Table 4). It is well accepted that plasma Zn is not a reliable indicator of Zn status unless animals are severely deficient in Zn (Underwood and Suttle, 1999). Soluble concentrations of Zn in ruminal fluid were increased by Zn supplementation (Table 4). Soluble Zn concentrations in ruminal fluid samples taken during the growing and finishing phases were higher (P < 0.05) in steers fed ZnProt than in those supplemented with ZnO. This would suggest that ZnProt was more soluble in the ruminal environment or that less Zn from ZnProt was converted into insoluble complexes in the rumen. Ruminal soluble Zn was slightly higher (P < 0.10) in steers fed ZnProt-B than in those fed ZnProt-A when samples were collected during the growing phase. The humoral immune response was assessed by measuring specific antibody titers to IBR following vaccination for IBR on d 70 of the growing phase. All steers were seronegative for IBR prior to vaccination. By d 14 following vaccination, 90% of the steers had developed titers to IBR. Zinc level or source did not affect IBR titers on d 14 or 28 after vaccination (Table 5). Skinfold thickness response to intradermal injection of PHA was affected by time, but not by Zn level nor source, or by a treatment time interaction (data not Table 6. Effect of zinc level and source on in vitro blastogenic response of peripheral blood lymphocytes Blastogenic response Control ZnO ZnProt-A ZnProt-B SEM cpm 10 3 Unstimulated Phytohemagglutinin 12.5 g/ml g/ml Pokeweed mitogen 10 g/ml a g/ml a a Control vs Zn treatments (P < 0.10). shown). Calves receiving a diet containing 17 mg Zn/ kg DM had a lower skinfold swelling response to PHA than calves fed 40 mg Zn/kg DM (Engle et al., 1997). The control diet used in the present study was about twice as high in Zn as the low Zn diet evaluated by Engle et al. (1997). The cell mediated immune response also was evaluated in vitro using a lymphocyte blastogenesis assay. Blastogenic response to PHA, a mitogen that stimulates predominatly T-lymphocytes, was similar across treatments (Table 6). Lymphocytes isolated from control steers had a slightly greater (P < 0.10) blastogenic response to PWM than steers supplemented with Zn regardless of Zn source. Pokeweed mitogen stimulates B- lymphocytes, but its stimulatory action is T-lymphocyte dependent. Results from the present study indicate that Zn supplementation of a diet containing 33 mg Zn/kg DM did not enhance cellular or humoral immune response in growing steers. Addition of 150 or 300 mg Zn/kg DM to a basal diet containing 60 mg Zn/kg DM did not affect lymphocyte blastogenesis, interleukin-1 production and cytotoxic activity, or the ability of neutrophils to phagocytize and kill bacteria in calves (Kincaid et al., 1997). Zinc supplementation of a diet containing 28 mg Zn/kg DM did not alter humoral or cellular immunity in growing lambs, even after ACTH was administered to simulate physiologic stress (Droke et al., 1998). Severe Zn deficiency (3.7 mg Zn/kg DM) did reduce lymphocyte responses to T-cell mitogens in lambs (Droke and Spears, 1993). Furthermore, a genetic disorder of Zn metabolism in dairy calves (lethal trait A46) results in severe Zn deficiency with subsequent thymic hypoplasia and impaired T-dependent immunity (Brummerstedt et al., 1971). Implications Zinc supplementation to a growing diet containing 33 mg Zn/kg diet increased gain in steers. Zinc requirements in growing steers appear to be higher for maximal growth than for maximal immune response. Supplementation of Zn proteinate during the finishing phase may improve steer gain and increase carcass weights relative to steers receiving a similar amount of Zn from ZnO. Zinc supplementation to a finishing diet, containing 26 mg Zn/kg diet, can improve carcass quality and yield grades. Literature Cited AAFCO Official Publication. Assoc. Am. Feed Control Officials, Inc., Oxford, IN. Beeson, W. M., T. W. Perry, and T. D. Zurcher Effect of supplemental zinc on growth and on hair and blood serum levels of beef cattle. J. Anim. Sci. 45: Brummerstedt, E., T. Flagstad, A. Basse, and E. Andresen The effect of zinc on calves with hereditary thymus hypoplasia (lethal trait A46). Acta. Pathol. Microbial. Scand. Sect. A 79:

6 2752 Spears and Kegley Cao, J., P. R. Henry, R. Guo, R. A. Holwerda, J. P. Toth, R. C. Littell, R. D. Miles, and C. B. Ammerman Chemical characteristics and relative bioavailability of supplemental organic zinc sources for poultry and ruminants. J. Anim. Sci. 78: Chesters, J. K Zinc. In: B. L. O Dell, and R. A. Sunde (ed.) Handbook of Nutritionally Essential Mineral Elements. pp Marcel Dekker Inc., New York. Droke, E. A., G. P. Gengelbach, and J. W. Spears Influence of level and source (inorganic vs organic) of zinc supplementation on immune function in growing lambs. Asian-Australas. J. Anim. Sci. 11: Droke, E. A., and J. W. Spears In vitro and in vivo immunological measurements in growing lambs fed diets deficient, marginal or adequate in zinc. J. Nutr. Immunol. 2: Engle, T. E., C. F. Nockels, C. V. Kimberling, D. L. Weaber, and A. B. Johnson Zinc repletion with organic or inorganic forms of zinc and protein turnover in marginally zinc-deficient calves. J. Anim. Sci. 75: Galyean, M. L., K. J. Malcolm-Callis, S. A. Gunter, and R. A. Berrie Effects of zinc source and level and added copper lysine in the receiving diet on performance by growing and finishing steers. Prof. Anim. Sci. 11: Gengelbach, G. P., J. D. Ward, and J. W. Spears Effect of dietary copper, iron, and molybdenum on growth and copper status of beef cows and calves. J. Anim. Sci. 72: Greene, L. W., D. K. Lunt, F. M. Byers, N. K. Chirase, C. E. Richmond, R. E. Knutson, and G. T. Schelling Performance and carcass quality of steers supplemented with zinc oxide or zinc methionine. J. Anim. Sci. 66: Kincaid, R. L., B. P. Chew, and J. D. Cronrath Zinc oxide and amino acids as sources of dietary zinc for calves: Effects on uptake and immunity. J. Dairy Sci. 80: Lardy, G. P., M. S. Kerley, and J. A. Paterson Retention of chelated metal proteinates by lambs. J. Anim. Sci. 70(Suppl. 1):314 (Abstr.). Malcolm-Callis, K. J., G. C. Duff, S. A. Gunter, E. B. Kegley, and D. A. Vermeire Effects of supplemental zinc concentration and source on performance, carcass characteristics, and serum values in finishing beef steers. J. Anim. Sci. 78: NRC Nutrient Requirements of Beef Cattle. 6th ed. National Academy Press, Washington, DC. NRC Nutrient Requirements of Beef Cattle. 7th ed. National Academy Press, Washington, DC. Nunnery, G. A., G. E. Carstens, and L. W. Greene Feedlot performance and carcass characteristics in steers fed different sources and levels of supplemental zinc. J. Anim. Sci. 74(Suppl. 1):294(Abstr.). Perry, T. W., W. M. Beeson, W. H. Smith, and M. T. Mohler Value of zinc supplementation of natural rations for fattening beef cattle. J. Anim. Sci. 27: Pond, W. G. and R. R. Oltjen Response of large and medium frame beef steers to protein and zinc supplementation of a corn silage-corn finishing diet. Nutr. Rep. Int. 38: Spain, J Tissue integrity: A key defense against mastitis infection: The role of zinc proteinates and a theory for mode of action. In: T. P. Lyons (ed.) Proc. 10th Ann. Symposium on Biotechnology in the Feed Industry. pp Nottingham University Press, Alltech Technical Publications, Nicholasville, KY. Spears, J. W Zinc methionine for ruminants: Relative bioavailability of zinc in lambs and effects on growth and performance of growing heifers. J. Anim. Sci. 67: Spears, J. W Organic trace minerals in ruminant nutrition. Anim. Feed Sci. Technol. 58: Spears, J. W., R. W. Harvey, and T. T. Brown, Jr Effects of zinc methionine and zinc oxide on performance, blood characteristics, and antibody titer response to viral vaccination in stressed feeder calves. J. Am. Vet. Med. Assoc. 199: Underwood, E. J., and N. F. Suttle Zinc. In: The Mineral Nutrition of Livestock. 3rd ed. pp CABI Publishing, New York. Ward, J. D., J. W. Spears, and E. B. Kegley Effect of copper level and source (copper lysine vs copper sulfate) on copper status, performance, and immune response in growing steers fed diets with or without supplemental molybdenum and sulfur. J. Anim. Sci. 71: