Growth-Promoting Efficacy of Tetrabasic Zinc Chloride and Two Sources of Zinc Oxide for Newly Weaned Pigs

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1 Growth-Promoting Efficacy of Tetrabasic Zinc Chloride and Two Sources of Zinc Oxide for Newly Weaned Pigs David H. Baker, Ioannis Mavromichalis and Douglas M. Webel University of Illinois Department of Animal Sciences and United Feeds, Inc., Sheridan, IN Pharmacologic levels of supplemental Zn are well established as growth promoters for newly weaned pigs. Feed-grade zinc oxide (ZnO) manufactured by the Waelz process dominates the feed-grade Zn market for pigs, and this source of ZnO also has been most heavily researched as a growth promotant for nursery pigs (Hahn and Baker, 1993; Hill et al., 1999; Mahan et al., 2000; Mavromichalis et al., 2000). Our research with chicks has demonstrated that Waelz ZnO (72% Zn) has a relative Zn bioavailability (RBV) of around 43% relative to analytical-grade ZnO (80.3% Zn). Another source of feed-grade ZnO is manufactured by the hydrosulfide process and contains about 78% Zn. Our research has shown that the RBV of Zn in this product is somewhat higher than that in analytical-grade ZnO (Edwards and Baker, 1999). A new source of Zn, tetrabasic zinc chloride (TBZC) with the formula Zn 5 Cl 2 (OH) 8 (containing about 60% Zn) is now available to the feed industry. The RBV of Zn in this product is about 20% higher than that in analytical-grade ZnO (Corless et al., 2000). Unlike Waelz ZnO which contains substantial quantities of cations other than Zn (e.g., 1.8% Fe, 1.7% Ca, 0.38% Na, 0.19% Mn, 0.16% Mg, and 0.10% Al), TBZC contains only traces of these contaminating cations. The growth-promoting ability of ZnO (or other sources of Zn) has taken on added significance in recent years because of the resistance-cross resistance concerns inherent in using antibacterial/antibiotic supplements in pig rations. Thus, routine antibiotic use in animal feeds (for growth promotion) may become illegal in the years ahead. The antibacterial properties of ZnO are well established in human medicine (Sordeberg et al., 1990), and therefore researchers focusing on early nutrition of nursery pigs are greatly interested in the growth-promoting efficacy of pharmacologic levels of Zn for nursery pigs. Illinois and United Feeds, Inc., Experiments. A typical phase-i nursery diet (100 mg Zn/kg provided in trace-mineral premix) was used in all experiments, and pigs were of either PIC or BMI genetics. The pigs were housed in nursery pens with woven-wire floors in environmentally-controlled nursery buildings. The first three experiments (Tables 1-3) compared a supplemental ZnO source with a low Zn RBV (Waelz process) to a ZnO source having a high Zn RBV (Hydrosulfide process). The supplemental Zn level was 1500 mg/kg in all of these experiments. Experiments 4 and 5 (Tables 4 and 5) were designed to compare Waelz ZnO to Zn 5 Cl 2 (OH) 8 (TBZC) at varying supplemental Zn levels, either in diets without (Exp. 4) or with added antibiotics i.e., ASP-250 (Exp. 5). Experiment 1 (Table 1). Pigs in this experiment were given a 7-d postweaning 108

2 adjustment period during which neither supplemental Zn nor antibiotics were fed. During the subsequent 21-d assay period, 1,500 mg Zn/kg was fed from either Waelz (W) ZnO or hydrosulfide (HS) ZnO, and no antibiotics were present in any of the assay diets. The lower dose (1,500 mg Zn/kg) of ZnO from a low RBV source (W) or a high RBV source (HS) was selected because it was felt that a less-than-optimal dose of ZnO would better detect potential efficacy differences between the two sources of ZnO. During the 1 st week of the assay, both sources of ZnO elicited a marked gain and feed efficiency response (P < ), and the responses were greater (P < 0.07) for HS than for W ZnO. For the entire 21-d feeding period, however, efficacy differences between W and HS ZnO did not exist. Also, in this trial, the weight gain response elicited by supplemental ZnO was due primarily to increased feed intake. Gut morphology (data not shown) was examined at trial termination in five pigs (medium-weight pig in each pen) per treatment, but ZnO supplementation had little effect on villus height or width or on crypt depth. Experiment 2 (Table 2). No antibiotics were present in the diets fed in this trial, but unlike the 7-d postweaning pretest feeding period of Exp. 1, the pigs in Exp. 2 were started on trial immediately after weaning at 21 d. A growth response (P < ) averaging 26% and a feed efficiency response (P < ) averaging 16% occurred due to 1500 mg Zn/kg added ZnO, regardless of ZnO source. Experiment 3 (Table 3). A 7-d postweaning pretest feeding period was employed in Exp. 3, and an antibiotic premix (ASP-250) was present in the diet during both the 7-d pretest period and the 11-d ZnO test period. Supplemental ZnO, regardless of source, increased both weight gain (P < ) and feed efficiency (P < ) during the initial 6 d and the entire 11 d of the experimental feeding period. There appeared to be some advantage in feed efficiency for the ZnO source (HS) that was high in Zn RBV over the source (W) that was low in Zn RBV. Experiment 4 (Table 4). Pigs were weaned at 15 d of age and placed immediately on experimental diets containing variable levels of Waelz ZnO or TBZC, but with no antibiotics. Feeding graded levels of supplemental Zn from ZnO produced a linear (P < ) response in both gain and gain/feed ratio. It appeared that the 3,000 mg Zn/kg dose from ZnO was required in this trail to stimulate weight gain. The quadratic (P < 0.07) gain response to TBZC suggested that 1,500 mg Zn/kg from TBZC was as effective as 3,000 mg Zn/kg for enhancing weight gain, although the feed efficiency response to TBZC was linear when Zn doses of 0, 1,500 and 3,000 mg/kg from TBZC were evaluated statistically. Averaged over both doses of supplemental Zn, TBZC produced a greater feed efficiency response than ZnO. Experiment 5 (Table 5). With ASP-250 present in all diets, early weaned pigs did not show a weight gain response to 1,500 mg Zn/kg addition in this experiment. Feed efficiency assessment, however, indicated a highly significant (P < ) response to TBZC but not to Waelz ZnO. 109

3 Conclusions: General conclusions from the experiments presented, plus others not shown here are itemized below. 1. Pharmacologic Zn dosing of early weaned or conventionally weaned pigs provides consistent and meaningful responses in pig performance. 2. Pharmacologic levels of Zn are more reliable than pharmacologic levels of Cu (i.e., copper sulfate) for growth promotion in nursery pigs. 3. ZnO or TBZC are efficacious Zn sources for nursery pigs in both the absence and presence of feed additive levels of antibiotics. 4. Zinc sulfate does not give consistent growth responses when fed to provide pharmacologic levels of dietary Zn. 5. At lower doses (i.e., 1,500 mg Zn/kg), there are performance advantages for a ZnO source whose Zn bioavailability is high (hydrosulfide-processed ZnO) compared with a ZnO source whose Zn bioavailability is low (Waelz-processed ZnO). 6. In the absence of dietary antibiotics, 3,000 mg Zn/kg from Waelz ZnO produces greater efficacy than 1,500 mg Zn/kg. 7. Tetrabasic Zn chloride (TBZC) is an excellent growth promoter, and 1,500 mg Zn/kg from TBZC is as effective as higher levels for stimulating weight gain and feed efficiency of newly weaned pigs consuming phase I diets in either the absence or presence of antibiotics. 8. Although pharmacologic Zn dosing with ZnO or TBZC consistently improves performance of nursery pigs, weight gain sometimes responds more than feed efficiency, but feed efficiency sometimes responds more than weight gain. 9. When evaluated immediately postweaning, responses to pharmacologic Zn levels often are not observed until after the first week of supplemental Zn feeding. Literature Cited Corless, A.B., T.M. Parr, and D.H. Baker Zinc bioavailability in tetrabasic zinc chloride and the dietary zinc requirement of young chicks fed a soy concentrate diet. Poultry Sci. (in press). Edwards, H.M., III and D.H. Baker Bioavailability of zinc in several sources of zinc oxide, zinc sulfate, and zinc metal. J. Anim. Sci. 77:

4 Hahn, J.D. and D.H. Baker Growth and plasma zinc responses of young pigs fed pharmacologic levels of zinc. J. Anim. Sci. 71: Hill, G.M., S.D. Carter, R.C. Ewan, D.C. Mahan, G.C. Shurson, and T.L. Veum Titration of pharmacologic doses of zinc in the nursery pig. J. Anim. Sci. 77(Suppl. 1):177 (Abstr.) Mahan, D.C., S.D. Carter, G.C. Cromwell, G.M. Hill, R.L. Harrold, A.J. Lewis, and T.L. Veum Efficacy of added zinc oxide levels with or without an antibacterial agent in the postweaning diets of pigs. Proc. Midwest ASAS, p. 41. Mavromichalis, I., C.M. Peter, T.M. Parr, D. Ganessunker, and D.H. Baker Growth promoting efficacy in young pigs of two sources of zinc oxide having either a high or a low bioavailability of zinc. J. Anim. Sci. (in press). Sordeberg, T.A., B. Sunzel, S. Hohn, T. Elmros, G. Hallman, and S. Sjoberg Antibacterial effect of zinc oxide in vitro. Scand. J. Plast. Reconstr. Surg. Hand Surg. 24:

5 Table 1. Effects of ZnO source on growth performance of nursery pigs fed diets without antimicrobial agents (Exp. 1) a, b Item Day 0 to 7 No added ZnO Dietary treatment c 1,500 mg Zn/kg 1,500 mg Zn/kg (Waelz) (Hydrosulfide) SEM Contrasts, P-value c, d None vs ZnO W vs HS 0.07 Day 7 to Day 14 to Day 0 to a Data are means of five pens of four pigs with an average initial body weight of 6.2 kg during a 21-d growth assay. b During a 7-d postweaning pretest period (21 to 28 d of age), all pigs had access to the basal diet containing no added ZnO or antimicrobial agents. c W = Waelz-processed ZnO (low Zn bioavailability); HS = hydrosulfide-processed ZnO (high Zn bioavailability). d = not significant P >

6 Table 2. Effects of ZnO source on growth performance of postweaned pigs fed diets without antimicrobial agents (Exp. 2) a Dietary treatment b Contrasts, P-value b, c Item No added ZnO 1,500 mg Zn/kg (Waelz) 1,500 mg Zn/kg (Hydrosulfide) SEM None vs ZnO W vs HS a Data are means of four pens of four pigs with an average initial body weight of 5.4 kg and an average initial age of 21 ± 2 d during a 17-d feeding period. b W = Waelz-processed ZnO (low Zn bioavailability); HS = hydrosulfide-processed ZnO (high Zn bioavailability). c = not significant P > Table 3. Effects of ZnO source on growth performance of nursery pigs fed diets containing antimicrobial agents (Exp. 3) a, b Item Day 0 to 6 No added ZnO Dietary treatment c 1,500 mg Zn/kg 1,500 mg Zn/kg (Waelz) (Hydrosulfide) SEM Contrasts, P-value c, d None vs ZnO W vs HS 0.10 Day 0 to a Data are means of five pens of four pigs with an average initial body weight of 6.2 kg during an 11- d growth period. b During a 7-d postweaning pretest period (21 to 28 d of age), all pigs had access to the basal diet containing no added ZnO but containing antimicrobial agents. c W = Waelz-processed ZnO (low Zn bioavailability); HS = hydrosulfide-processed ZnO (high Zn bioavailability). d = not significant P >

7 Table 4. Effects of increasing doses of zinc from zinc oxide or tetrabasic zinc chloride on growth performance of postweaned pigs fed diets without antimicrobial agents (Exp. 4) a Treatments b 1. No added Zn (control) 2. 1,500 mg Zn/kg from ZnO 3. 3,000 mg Zn/kg from ZnO 4. 1,500 mg Zn/kg from TBZC 5. 3,000 mg Zn/kg from TBZC Pooled SEM Contrasts, P-valine c Control vs added Zn ZnO vs TBZC ZnO linear ZnO quadratic TBZC linear TBZC quadratic 0.07 a Data are means of five pens of six pigs with an average initial body weight of 5.2 kg and an average initial age of d during a 21-d feeding period. b ZnO (Waelz) vs. tetrabasic Zn chloride (TBZC). c = not significant P > Table 5. Effects of 1,500 ppm of zinc from zinc oxide or tetrabasic zinc chloride on growth performance of postweaned pigs fed diets with an antimicrobial agent (Exp. 5) a Treatments b 1. No added Zn (control) 2. 1,500 mg Zn/kg from ZnO 3. 1,500 mg Zn/kg from TBZC Pooled SEM Contrasts, P-valine c Control vs ZnO ZnO vs TBZC a Data are means of eight pens of six pigs with an average initial body weight of 5.2 kg and an average initial age of during a 19-d feeding period. b ZnO (Waelz) vs. tetrabasic Zn chloride (TBZC) c = not significant P >