Meeting the Trce Minerl Needs of Diry Cows Mike T. Soch, Dn J. Tomlinson, Jeff M. Defrin nd Terry L. Wrd Zinpro Corportion 10400 Viking Dr., Ste. 240 Eden Pririe, MN 55374 msoch@zinpro.com Tke Home Messges Current Diry NRC (2001) requirements for coblt, mngnese nd zinc my not be sufficient to meet the needs of the cow. Trce minerl content of feedstuffs nd minerl content of wter cn be quite vrible. Antgonists nd stress ffect trce minerl bsorption nd utiliztion. Supplying portion of the trce minerls from minerl sources, in which the metl is bound to n mino cid, reduces the effect of ntgonists nd stress on minerl vilbility. 1. Introduction In Jnury 2001, the Seventh Revised Edition of the Diry NRC ws introduced nd in mny respects ws vst improvement over previous editions. For exmple, in the Sixth Revised Edition of the Diry NRC (1989), trce minerl requirements were the sme for 1700 lb mture mid-lcttion cow consuming 55 lb dry mtter (DM) nd producing 70 lb milk s for 1300 lb first clf heifer, 20 dys fresh, consuming 42 lb DM nd producing 100 lb milk. With the exception of coblt (Co) nd selenium (Se), the Seventh Revised Edition of the Diry NRC (2001) introduced fctoril pproch for determintion of trce minerl requirements (Tble 1). This consists of summing the trce minerl needs of wened diry cttle for mintennce, growth, pregnncy nd lcttion, then dividing this sum by the DM intke (DMI) to determine the required trce minerl concentrtion. An bsorption coefficient is then pplied to this sum to ccount for differences in biovilbility between trce minerl sources. This pproch ccounts for the impct of DMI on trce minerl intke, in ddition to differences in trce minerl needs due to level of milk production, growth rte nd stge of gesttion (Figure 1). Trce minerl requirements for unwened clves did not chnge substntilly from the Sixth Revised Edition. 2. Reserch Updte on Trce Minerl Requirements While the Seventh Revised Edition of the Diry NRC (2001) mde vst improvements concerning trce minerl requirements of diry cttle, recent reserch indictes tht current NRC (2001) requirements for some trce minerls my not be sufficient. 2.1 Zinc (Zn) Requirement for Dry Cows Required dietry Zn concentrtions for dry nd prefresh cows were reduced from 40 ppm (NRC, 1989) to 22 to 30 ppm (NRC, 2001), depending upon ge nd DMI. However, Tennessee reserchers (Cmpbell nd Miller, 1998), found tht feeding n dditionl 800 mg Zn (400 mg from Zn methionine (Met; ZIN- PRO zinc methionine) nd 400 mg from Zn sulfte) to lte gesttion cows, which were lredy receiving diet contining 102 ppm Zn, resulted in improved fertility nd helth postclving. Cows fed dditionl Zn preprtum hd fewer dys to first estrus, less udder edem when cows were fed diets high in iron, nd tended to hve fewer dys to first service. More recently, reserch with other species hs found tht feeding high levels of Zn to pregnnt nimls or injecting Zn into eggs improved gut development nd helth of offspring. Cndin reserchers found tht feeding sows n dditionl 250 ppm Zn from Zn mino cid (AA) complex (Avil Zn) during the lst trimester of pregnncy, resulted in improved intestinl development of pigs, s indicted by incresed villous height (Cine et l., 2001). Furthermore, intestinl defenses of these pigs ginst pthogens ppered to hve 2008 Penn Stte Diry Cttle Nutrition Workshop 61
been improved s indicted by n incresed number of intrepithelil lymphocytes. Similrly, North Crolin reserchers found tht injecting ZnMet (ZINPRO) in ovo t seventeen dys of incubtion resulted in significnt increses in brush-border enzymes nd trnsporters nd in jejunl villous surfce re (Tko et l., 2005). Results of these studies indicte tht incresing Zn supply to pregnnt diry cttle hs the potentil to improve gut helth nd development of young clves. 2.2 Mngnese (Mn) Requirement Required dietry Mn concentrtions were decresed from 40 ppm (NRC, 1989) to 13 to 22 ppm (NRC, 2001). It should be noted tht there ws limited mount of dt vilble to the NRC committee to ssist them in estblishing Mn requirement for diry cttle. Recently, reserch t The Ohio Stte University found the verge dry nd lctting cow must consume 580 mg Mn/d in order to mintin zero Mn blnce (equtes to 49 ppm Mn for dry cow diets nd 28 ppm Mn for lctting cow diets; Weiss nd Soch, 2005). While consuming 580 mg Mn/d resulted in the verge diry cow being in zero Mn blnce, number of cows consuming up to 1000 mg Mn/d were still in negtive Mn blnce (Figure 2). Furthermore, growing nd pregnnt diry cttle should be in positive Mn blnce due to tissue ccretion. Therefore nutritionists should formulte diets to provide in excess of 580 mg Mn/cow/d to ensure tht most cows in the diry herd re t lest mintining Mn blnce. One potentil benefit of incresing Mn supply to diry cttle is improved reproduction. Mngnese is necessry for synthesis of cholesterol, the precursor of the steroids, estrogen, progesterone nd testosterone (Underwood nd Suttle, 1999). Insufficient steroid production results in decresed circulting concentrtions of these reproductive hormones resulting in bnorml sperm production in mles nd irregulr estrous cycles in femles (Miller et l., 1988). The ovry is reltively rich in mngnese nd ppers to be prticulrly sensitive to dietry deficiencies of mngnese (Hidiroglou, 1979). In ddition, vginl Mn concentrtions re higher in cycling thn in nestrous ruminnts (Hidiroglou, 1976). North Crolin reserchers found tht incresing Mn supplementtion of growing beef heifers numericlly improved fertility. In this study, heifers were fed bsl diet contining 15.8 ppm of Mn supplemented with 0, 10, 30 nd 50 ppm Mn from Mn sulfte (Hnsen et l., 2006). Incresing supplementl Mn from 0 to 50 ppm numericlly incresed heifers showing estrus fter prostglndin injection from 40 to 50%, first service conception rtes from 45 to 60%, nd overll pregnncy rte from 60 to 75% (Tble 2). Inbility to detect significnt tretment effects despite sizble improvements in these mesurements my be ttributed to insufficient number of nimls ssigned to the study. Similrly, results from Nocek et l. (2006) indicte tht incresing Mn supplementtion of diry diets improves fertility. In this study, lctting diry cttle were either supplemented with Zn, Mn, copper (Cu) nd Co t 75% of NRC (2001) requirements using AA complexes nd glucoheptonte (75Z), 100% of NRC (2001) requirements for these trce minerls using either AA complexes nd glucoheptonte (100Z) or sulftes (100S), or combintion of sulftes, AA complexes nd glucoheptonte to provide lctting diry cttle with Zn nd Cu t 100% NRC (2001) requirements nd Mn nd Co t 3.3 nd 9.1 times NRC (2001) requirements, respectively (Z/S). Compred to the other tretments, cows fed the Z/S tretment hd fewer dys to first estrus in lcttions one nd two nd incresed first service conception rte nd pregnncy rte in lcttion two (Tble 3). While there were differences in trce minerl source nd coblt concentrtion between the 75Z, 100Z, 100S nd Z/S tretments, the most notble difference between the Z/S tretment nd the other tretments ws the mount of Mn supplemented during lcttion. 2.3 Coblt Requirement The Co requirement listed in the Diry NRC (2001) is 0.11 ppm DM. However, reserchers t Wshington Stte University found tht lctting cows, in prticulr multiprous cows, benefit from consuming diets with Co levels well in excess of NRC (2001) requirements (Kincid et l., 2003). In the study, incresing Co supplementtion from 0 to 25 mg/hd/d incresed 62 November 12-13 Grntville, PA
production of milk nd 3.5% ft-corrected milk in multiprous cows but not in primiprous cows. Lck of response by first clf heifers to dditionl Co my be due to first-clf heifers hving higher Co sttus thn mture cows, s indicted by higher liver Co nd serum vitmin B12 concentrtions (Co is required for the formtion of vitmin B12). Anlysis of diet nd milk Co concentrtions indicted tht cows were in negtive Co blnce, ssuming tht 2% of dietry Co ws bsorbed by the niml (Kincid et l., 2003; Tble 4). This ssumption is consistent with coblt bsorption estimtes reported in the literture (Looney et l., 1976). In order for cows to be in zero Co blnce, they would need to bsorb 37, 20 nd 11% of dietry Co, bsed upon the Co intkes of 8.8, 15.6 nd 29.9 mg/hd/d, respectively (Tble 4). Results of Kincid et l. (2003) re supported by Cndin reserch which found tht erly lcttion cows fed diets contining 0.66 ppm supplementl Co hd low serum vitmin B12 concentrtions (Girrd et l., 2005). Injecting cows weekly with 10 mg vitmin B12 incresed production of energy-corrected milk, milk solids nd milk ft (Girrd nd Mtte, 2005). In ddition to lcttion being drin on Co/vitmin B12, feeding high concentrte diets, typicl of those fed to lctting diry cows, ppers to increse the Co requirement. Reserch hs demonstrted tht incresing the concentrte to forge rtio reduces the mount of vitmin B12 flowing from continuous culture fermentors (Allen, 1986; concentrte portion of diet incresed from 30 to 60%) nd decreses true vitmin B12 content of solid nd liquid ssocited bcteri (Sntschi et l., 2005; concentrte portion of the diet incresed from 40 to 60%). Incresing supplementl Co concentrtion from 0.0 to 0.5 ppm incresed the mount of vitmin B12 flowing from continuous culture fermentors (Allen, 1986) when fermentors were fed 40% forge diet. The decrese in true vitmin B12 production with incresing levels of concentrte my be ttributed to incresing levels of nonfiber crbohydrtes (NFC). Schwb et l. (2004) found tht cows fed 40% NFC diet hd lower pprent ruminl vitmin B12 synthesis thn cows fed 30% NFC diet (73 vs. 100 mg/d). Nonfiber crbohydrte source my lso ffect ruminl production of vitmin B12 nd required dietry Co concentrtion. Incresing dietry Co concentrtion from 0 to 0.15 mg dded Co/kg DM incresed ruminl B12 concentrtions of steers fed corn-bsed diets but not steers fed brley-bsed diets (Tble 5; Tiffny nd Spers, 2005). Together, these studies indicte tht current NRC (2001) requirements pper to be insufficient to meet the Co requirements of erly lcttion diry cows nd tht Co requirements of diry cttle pper to be dependent upon level of milk production, NFC content of the diet nd NFC source. 3. Fctors Affecting Absorption Coefficients Other fctors tht need to be considered when using the NRC (2001) to determine the mount of trce minerls to dd to diets of diry cttle re the bsorption coefficients. In the Seventh Revised Edition of the Diry NRC (2001), bsorption coefficients were given for feedstuffs nd inorgnic sources of trce minerls. Absorption coefficients used to clculte required dietry concentrtions (Tble 1) were those pplied to endogenous trce minerls in feedstuffs. In most cses, supplementl sources of trce minerls hve higher bsorption coefficients, thus reducing required dietry concentrtions. In ddition, bsorption coefficients used to clculte requirements ssume norml intkes of elements tht ffect uptke of trce minerls. A sfety fctor is not included to ccount for vritions in consumption of ntgonists. Nutrition dvisors need to be wre of trce minerl nd ntgonist content of dietry ingredients nd djust their recommendtions ccordingly. Adjusting trce minerl recommendtions in response to chnges in intkes of trce minerls nd ntgonists cn be difficult becuse feedstuffs cn differ substntilly from lot to lot in trce minerl content. This is especilly true when forges nd commodities re cquired from severl sources. Agronomic prctices, hrvest methods nd soil types impct Zn, Cu nd 2008 Penn Stte Diry Cttle Nutrition Workshop 63
Mn s well s molybdenum (Mo), sulfur (S) nd iron (Fe) content of feedstuffs nd forges. Another fctor tht cn ffect trce minerl vilbility is soil consumption. British reserchers found tht plsm Cu levels of Cu deficient ewes incresed when supplemented with Cu (Suttle et l., 1976). However, plsm Cu levels of Cu deficient ewes did not increse when supplementl Cu ws dded to diets contining 10% soil, indicting tht the soil ws reducing Cu bsorption. Soil consumption on diries vries substntilly depending upon hrvest conditions, storge structures, conditions upon emptying of storge structures nd grzing conditions. In summry of 450 fresh, fll hrvested, lflf silge smples, sh content rnged from 4.9 to 16.0% DM (verge 10.2% DM; Figure 2; D. Tysom, Dirylnd Lbortories, St. Cloud, MN; personl communiction), indicting tht the degree of soil contmintion is vrible nd cn be potentilly quite high. In smpling of byproducts nd forges from Cliforni nd Minnesot, reserchers nd nutrition dvisors found tht Fe, Zn, Cu nd Mn content of feed ingredients cn devite severl fold (DePeters et l., 2000; Olson et l., 2002; Tble 6). For instnce, Fe content of lflf silge rnged from 116 to 866 ppm nd Cu content of whet mill run rnged from 2 to 153 ppm (Tble 6). Alflf silge fed t rte of 10 lb DM/hd/d, or 20% of DM, would contribute between 23 nd 173 ppm Fe. Feeding 4 lb/hd/d of whet mill run would contribute between 0.2 nd 12 ppm Cu. Thus minerl content of feed ingredients cn, in some situtions, increse the need for supplementl trce minerls nd in other situtions limit the mount of trce minerls tht cn sfely be dded to the diet. Minerls supplied by wter cn lso ffect bsorption of trce minerls. A summry of 3,651 wter smples indicted tht C, Cl, N, Mg, S, Fe nd Mn content of wter cn be vrible nd hve significnt effect on intke of these minerls (Soch et l., 2003; Tble 7). For instnce, S content of wter rnged from 0 to 1,197 ppm (Tble 7). Lctting diry cows drinking wter contining 250 ppm S would consume 31 g of dditionl S (ssuming cows re consuming 52.9 lb DM nd 31.6 gllons of wter). This trnsltes into n dditionl 0.13 percentge units of dietry S. Fortuntely, on most diries, there re only one or two sources of wter. Thus, most of the vrition is between diries, in contrst to feed ingredients tht cn vry from lot to lot within diry. 3.1 Absorption Coefficients Are Not Sttic Due to fluctutions in trce minerl nd ntgonist intke, true bsorption coefficients of trce minerls vry. This vrition impcts the mount of trce minerls needed to meet the true requirements of the niml. For exmple, incresing dietry S intke from 0.20% to 0.60% due to consumption of high S wter reduces Cu bsorption coefficient by 50% (NRC, 2001; Tble 8). Chnges in Mo intke lso impct dietry Cu requirements, but to lesser extent thn chnges in dietry S. Absorption coefficients reported for Cu in Tble 8 do not reflect the ntgonistic effects of high dietry levels of Fe nd Zn. 4. Formulting Diets to Meet Trce Minerl Requirements of the Animl Due to potentilly lrge fluctutions in dietry trce minerls nd ntgonists, formulting diets to meet the trce minerl requirements of diry cttle cn be difficult. Nutrition dvisors cn employ one of three methods to compenste for these vritions: 1. Implement n intensive feed nlysis progrm, nlyzing ll lots of commodities, feedstuffs nd forges, nd lter trce minerl fortifiction levels ccordingly. The logistics of this progrm would be extremely difficult; 2. Substntilly increse dietry concentrtions of inorgnic trce minerl sources. This strtegy does not ccount for potentil trce minerl interctions nd my, in relity, negtively impct niml performnce nd the environment; or 3. Feed levels of dietry trce minerls t or slightly bove NRC (2001) requirements nd include Zinpro Performnce Minerls t the recommended levels. 64 November 12-13 Grntville, PA
4.1 Feeding Lower Levels of Trce Minerls with Portion Supplied by Performnce Minerls Reduces the Risk for Trce Minerl Toxicity Trce minerls fed in excess of requirements my not only impede bsorption of other trce minerls, but my lso be toxic. For most trce minerls there is reltively lrge mrgin between mounts needed to meet requirements nd the mximum tolerble level. However, for Cu, the sfety mrgin is reltively low. Copper toxicities hve been reported in Jersey cttle t dietry levels of 37 ppm Cu, pproximtely three times the NRC (2001) requirement (Olson et l., 1999). 4.2 Performnce Minerls Are Less Affected by Antgonists nd Stress Thn Inorgnic Sources The difference in bsorption of inorgnic sources of trce minerls such s Zn sulfte nd more biovilble complexed sources such s ZnMet (ZINPRO) re miniml when level of ntgonists re low, but increse when level of ntgonists re high. This is illustrted in study conducted by Wedekind et l. (1992). When chicks were fed diets formulted to contin only crystlline mino cids to minimize dietry fiber nd phytte levels, the differences in vilbility of Zn from Zn sulfte nd Zn from ZnMet were, lthough significnt, miniml (Figure 4). However, when chicks were fed commercil diets formulted with soyben mel s the source of mino cids nd hence contined higher dietry levels of ntgonists such s fiber nd phytte, the difference in vilbility of Zn from Zn sulfte nd ZnMet incresed drmticlly (Figure 4). Formulting diets contining lower levels of trce minerls with portion of the trce minerls supplied by orgnic sources increses the probbility tht trce minerl requirements of nimls will be met when dietry levels of ntgonists re high but minimizes the risk of toxicity when dietry levels of ntgonists re low. The bility of nimls to bsorb nd utilize trce minerls is ffected by not only ntgonists but lso by stress level. In study conducted t Colordo Stte University (Nockels et l., 1993), Cu blnce ws exmined prior to subjecting clves to Cu restricted diets nd induced stress. Clves then received Cu restricted diet for nine dys with stress being induced by feed nd wter restriction for three of the nine dys. Following the period of Cu restriction nd induced stress, Cu blnce ws mesured with clves receiving Cu supplied by either Cu sulfte or Cu lysine (CuLys; CuPLEX ). Results of the study showed tht prior to the period of Cu restriction nd induced stress, clves retined 3.6 mg or 8.1% of ingested Cu from Cu sulfte nd 6.5 mg or 14.3% of ingested Cu from CuLys. Following the period of Cu restriction nd stress, clves retined 1.5 mg or 3.3% of Cu from Cu sulfte nd 6.9 mg or 15.0% of Cu from CuLys, indicting tht stress hd greter impct on retention of Cu from inorgnic sources thn from CuLys. 4.3 Performnce Minerls Improve Animl Performnce Reserch hs shown tht replcing inorgnic sources of trce minerls with Performnce Minerls improves niml performnce. In summry of six diry trils, replcing 360 mg Zn from inorgnic Zn, 200 mg Mn from inorgnic Mn, 125 mg Cu from inorgnic Cu nd 12 or 25 mg Co from inorgnic Co with similr mounts from ZnMet, MnMet, CuLys nd Co glucoheptonte (4 Plex), resulted in improved fertility nd incresed production of milk, energy-corrected milk nd milk components (Kellogg et l., 2003; Ferguson et l., 2004; Kincid nd Soch, 2004; Tble 9). Control nd tretment diets in ll studies met or exceeded trce minerl requirements. Liver biopsies were collected in only two of the six studies, thus it cn only be ssumed tht cows ssigned to most of these studies hd dequte trce minerl sttus. A study completed in Florid indictes tht cows with dequte to high trce minerl sttus benefited when sulfte forms of Zn, Mn, Cu nd Co were replced with Zinpro Performnce Minerls (Bllntine et l., 2002). Despite control nd tretment diets contining 231%, 628%, 153% nd 1,364% of NRC (2001) requirements for Zn, Mn, Cu nd Co, respectively, cows fed Performnce Minerls (Avil 4) produced more milk nd energy-corrected milk, hd fewer dys open, tended to be more likely to be pregnnt t 150 d postprtum nd tended to hve fewer clw lesions t 75 dys postprtum. 2008 Penn Stte Diry Cttle Nutrition Workshop 65
5. Trce Minerl Recommendtions Diry cttle trce minerl recommendtions from Zinpro Corportion re provided in Tble 10. As noted bove, we believe tht the NRC (2001) Co nd Mn requirements for diry cttle nd the Zn requirements for dry nd prefresh cows re lower thn desired nd our recommendtions reflect these sentiments. For the other trce minerls, our recommendtions mirror NRC (2001) requirements. Agin, requirements given in the new NRC (2001) do not contin sfety fctor. However, severl sfety fctors hve been built into recommendtions given in Tble 10 including: 1. Recommendtions re supplementl, not totl diet. Requirements given in NRC (2001) re totl diet; 2. NRC requirements given in Tble 1 nd Figure 1 of this pper re clculted using bsorption coefficients given for feedstuffs. Absorption coefficients given for sulftes nd Performnce Minerls re higher thn those used for feedstuffs, reducing the mount of supplementl trce minerls needed; nd 3. Recommendtions include portion of the trce minerls being supplied by Performnce Minerls. Absorption of Performnce Minerls is less ffected by stress nd ntgonists. 6. Comments Regrding Iron Recommendtions In the NRC (2001), it is stted iron deficiency in dult cttle is very rre in prt becuse their requirement is reduced, but lso becuse iron is ubiquitous in the environment, nd soil contmintion of forges (nd soil ingested by nimls on psture) generlly ensures tht iron needs of the dult will be met or exceeded Thus mny nutritionists hve either reduced or removed supplementl iron from diets of dult diry cttle. It should be noted tht there is limited reserch vilble exmining the effect of feeding dult diry cttle supplementl iron. Most recently reserch hs exmined the effect of feeding steers nd diry cttle supplementl iron on gossypol bsorption. Adding 150, 300, 450 nd 600 ppm of iron from iron sulfte to diets of steers consuming pproximtely 10 g of gossypol per dy, reduced plsm totl gossypol concentrtions by 30.7, 27.0, 41.7 nd 53.3%, respectively (Sntos et l., 2005). Weight gin of steers ws unffected by tretment. Due to the potentil concerns with gossypol nd its effect on fertility (Sntos et l., 2003), there my be beneficil effects of supplementing diry cttle consuming diets contining lrge mounts of cottonseed with iron. McCughey et l. (2005) found tht supplementing diets of lctting diry cttle with 250 nd 500 ppm of iron from iron sulfte reduced totl plsm gossypol concentrtions by 23.7 nd 28.2%, respectively. While dding 250 nd 500 ppm of iron from iron sulfte decresed milk yield by 3.87 nd 7.63%, respectively, milk energy output incresed 0.7% when cows were fed the diet contining 250 ppm iron. In humns, iron deficiency is common nutritionl problem despite iron being one of the most common elements on erth (Dllmn, 1990). Possible explntions include common forms of iron being reltively insoluble nd poorly bsorbed nd phytte nd fiber, in diets contining whole grins nd legumes, reducing iron vilbility (Dllmn, 1990). In ddition, iron found in soil ppers to be of limited vilbility. New Zelnd reserchers found tht feeding sheep diets contining 712 to 978 ppm of iron from soil for 76 dys did not increse significntly iron content of liver (Grce et l., 1996). Children nd women of child bering ge pper to be most prone to iron deficiency (Dllmn, 1990). With pregnncy, erythrocyte volume increses s much s 18 to 30% in the lter stges of gesttion (King nd Weininger, 1990). Clerly more reserch is needed to determine if cttle in lte pregnncy re prone to iron deficiency or to determine if supplementing diry cttle with low to moderte levels of iron cn reduce gossypol bsorption while mintining or enhncing performnce of cttle. 7. Comments Regrding Iodine Recommendtions In My, 2000, FDA Office of Regultory Affirs revised the Complince Policy Guide for ethylenedimine dihydroiodide (EDDI) llowing producers to feed cttle 49.9 mg EDDI (provides pproximtely 66 November 12-13 Grntville, PA
40 mg iodine) per dy. However, in October, 2000, Shron Benz from FDA sent out n emil noting tht while diry producers were llowed to feed 49.9 mg of EDDI, it is the producer s responsibility to mke sure tht the milk is sfe. She noted tht...up to 30 mg of EDDI/dy could be fed without cusing unsfe iodine levels in the milk. In summry of studies, Irish reserchers found tht diry cttle needed to receive 30 to 60 mg iodine per dy to mintin dequte iodine sttus s noted by plsm inorgnic iodine concentrtions (Rogers, 1999). It should be noted tht in severl of these studies, potssium iodide ws the source of supplement iodine. As compred to EDDI, iodine voltiliztion tends to be greter with potssium iodide (NRC, 2001). Thus higher levels of iodine from potssium iodide my need to be fed to provide diry cttle with the sme mount of bsorbble iodine s compred to providing supplementl iodine in the form of EDDI. In the Irish studies, milk iodine levels rnged from 0.02 ppm to 0.4 ppm (Rogers, 1999). According to current guidelines, humns cn sfely consume up to 1000 μg I per dy (Hetzel, 1990). Diry products commonly provide bout 50% of the totl iodine consumed by humns (Rogers, 1999). Milk iodine concentrtions greter thn 0.3 ppm re considered high (Rogers, 1999) with milk processors tking ction with producers when milk iodine levels exceed 0.8 ppm. Clerly more reserch needs to be conducted with iodine to determine how much EDDI needs to be fed to mintin dequte iodine sttus in diry cttle nd how much EDDI cn be fed to cows while mintining sfe levels of iodine in milk. 8. Summry The Seventh Revised Edition of the Diry NRC (2001) mde significnt positive improvements in identifying the trce minerl requirements of diry cttle. However, more recent reserch indictes tht (NRC, 2001) Mn nd Co requirements for lte gesttion nd lctting diry cttle nd Zn requirements for lte gesttion cttle my not be dequte. Furthermore, the bsorption coefficients used to clculte requirements ccount for limited ntgonistic reltionships between minerls. The tsk of rtion formultion is further complicted by substntil vrition in trce minerl nd ntgonist content of feedstuffs nd wter. These fluctutions cn hve significnt impct on bsorption coefficients, ffecting the trce minerl requirements of the niml, s well s the mount of trce minerls tht cn sfely be dded to the diet. Nutrition dvisors cn compenste for fluctutions in trce minerl nd ntgonist content of feedstuffs by either substntilly incresing fortifiction levels with inorgnic sources or by feeding trce minerls t or slightly bove NRC (2001) requirements with portion of the minerls supplied by Performnce Minerls. By supplementing trce minerls t or slightly bove NRC (2001) requirements nd including Performnce Minerls t the recommended levels, nutrition dvisors: 1. Increse the probbility of meeting requirements when consuming high levels of ntgonist; 2. Increse the probbility of meeting requirements of the cow during stress; 3. Reduce the risk of trce minerl toxicity; nd 4. Improve niml performnce. 9. References Allen, M. 1986. Effect of coblt supplementtion on crbohydrte nd nitrogen utiliztion by ruminl bcteri in continuous culture. M.S. Thesis, University of Minnesot. Bllntine, H. T., M. T. Soch, D. J. Tomlinson, A. B. Johnson, A. S. Fielding, J. K. Sherer nd S. R. vn Amstel. 2002. Effects of feeding complexed zinc, mngnese, copper nd coblt to lte gesttion nd lctting diry cows on clw integrity, reproduction nd lcttion performnce. Prof. Anim. Sci. 18:211-218. Cine, W., M. McFll, B. Miller, D. Onderk, R. Kirkwood, S. Jikrn nd T. Fkler. 2001. Intestinl development of wened pigs from zinc mino cid complex supplemented gestting sows. Bnff Pork Seminr, vol. 12. Cmpbell, M. H. nd J. K. Miller. 1998. Effect of supplementl dietry vitmin E nd zinc on reproductive performnce of diry cows nd heifers fed excess iron. J. Diry Sci. 81:2693-2699. 2008 Penn Stte Diry Cttle Nutrition Workshop 67
Dllmn, P. R. 1990. Iron. Pges 241-250 in Present Knowledge in Nutrition. M. L. Brown, ed. Interntionl Life Sciences Institute Nutrition Foundtion, Wshington, D.C. DePeters, E. J., J. G. Fdel, M. J. Arn, N. Ohnesin, M. A. Etchebrne, C. A. Hmilton, R. Hinders, M. D. Mloney, C. A. Old, T. J. Riordn, H. Perez-Monti nd J. W. Pres. 2000. Vribility in the chemicl composition of seventeen selected by-product feedstuffs used by the Cliforni Diry Industry. Prof. Anim. Sci. 16:69 99. Ferguson, J. D., D. J. Tomlinson, nd M. T. Soch. 2004. Effects of inorgnic nd orgnic (4-Plex ) trce minerl supplementtion on milk production nd reproduction. J. Diry Sci. 87(Suppl. 1):117 bstrct Girrd, C. L., nd J. J. Mtte. 2005. Effects of intrmusculr injections of vitmin B12 on lcttion performnce of diry cows fed dietry supplements of folic cid nd rumen-protected methionine. J. Diry Sci. 88:671 676. Girrd, C. L., H. Lpierre, J. J. Mtte nd G. E. Lobley. 2005. Effects of dietry supplements of folic cid nd rumen-protected methionine on lcttionl performnce nd folte metbolism of diry cows. J. Diry Sci. 88:660 670. Grce, N. D., J. R. Rounce nd J. Lee. 1998. Effect of soil ingestion on the storge of Se, vitmin B12, Cu, Cd, Fe, Mn, nd Zn in the liver of sheep fed Lucerne pellets. NZ J. Agric. Res. 39:325-331. Hnsen, S. L., J. W. Spers, K. E. Lloyd, nd C. S. Whisnnt. 2006. Growth, reproductive performnce, nd mngnese sttus of heifers fed vrying concentrtions of mngnese. J. Anim. Sci. 84:3375-3380. Hetzel, B. S. 1990. Iodine deficiency: An interntionl public helth problem. Pges 308-313 in Present Knowledge in Nutrition. M. L. Brown, ed. Interntionl Life Sciences Institute Nutrition Foundtion, Wshington, D.C. Hidiroglou, M. 19769. Concentrtion of mngnese in the tissue of cycling nd nestrous ewes. Cn. J. Comp. Med. 40:306-309. Hidiroglou, M. 1979. Trce element deficiencies nd fertility in ruminnts: A review. J. Diry Sci. 62:1195-1206. Kellogg, D. W., M. T. Soch, D. J. Tomlinson nd A. B. Johnson. 2003. Review: Effects of feeding coblt glucoheptonte nd metl specific mino cid complexes of zinc, mngnese, nd copper on lcttion nd reproductive performnce of diry cows. Prof. Anim. Sci. 19:1 9. Kincid, R. L., L. E. Lefebvre, J. D. Cronrth, M. T. Soch nd A. B. Johnson. 2003. Effect of dietry coblt supplementtion on coblt metbolism nd performnce of diry cttle. J. Diry Sci. 86:1405 1414. Kincid, R. L. nd M. T. Soch. 2004. Inorgnic versus complexed trce minerl supplements on performnce of diry cows. Prof. Anim. Sci. 20:66-73 King, J. C. nd J. Weininger. 1990. Pregnncy nd lcttion. Pges 314-319 in Present Knowledge in Nutrition. M. L. Brown, ed. Interntionl Life Sciences Institute Nutrition Foundtion, Wshington, D.C. Looney, J. W., G. Gille, R. L. Preston, E. R. Grhm, nd W. H. Pfnder. 1976. Effects of plnt species nd coblt intke upon coblt utiliztion nd rtion digestibility by sheep. J. Anim. Sci. 42:693 698. McCughey, K. M., E. J. DePeters, P. H. Robinson, J. E. P. Sntos, J. W. Pres, nd S. J. Tylor. 2005. Impct of feeding Uplnd cottonseed, with or without crcked Pim cottonseed with incresing ddition of iron sulfte, on productivity nd plsm gossypol of lctting diry cttle. Anim. Feed Sci.Tech. 122:241-256. Miller, J. K., N. Rmsey nd F. C. Mdsen. 1988. The trce elements. In: The Ruminnt Animl. D. C. Church, ed. Prentice Hll, Englewood Cliffs, NJ, pp. 342-400 Ntionl Reserch Council. 1989. Nutrient Requirements of Diry Cttle. 6th rev. ed. Ntl. Acd. Sci. Wshington, D.C. Ntionl Reserch Council. 2001. Nutrient Requirements of Diry Cttle. 7th rev. ed. Ntl. Acd. Sci. Wshington, D.C. Nocek, J. E, M. T. Soch nd D. J. Tomlinson. 2006. The effect of trce minerl fortifiction levels nd source performnce of diry cttle. J. Diry Sci. 89:2679-2693. Nockels, C. F., J. DeBonis nd J. Torrent. 1993. Stress induction ffects copper nd zinc blnce in clves fed orgnic nd inorgnic copper nd zinc sources. J. Anim. Sci. 71:2539 2545. Olson, W. G., M. Murphy, N. J. Auz, J. G. Linn nd D. Shw. 1999. Review of copper toxicity in diry cttle. In: Proceedings of Minnesot Diry Helth Conference, Bloomington, MN, pp. 167-173 Olson, W. G., N. J. Auz, M. Schmitt, H. Chester-Jones, J. Linn nd M. Murphy. 2002. Survey of copper nd other minerls in Minnesot Holstein Diry Cttle: Soil, feed nd liver concentrtions. In: Proceedings of Minnesot Diry Dys, University of Minnesot, St. Pul, pp 79 84 Rogers, P. A. M. 1999. Iodine supplementtion of cttle. Finl report for Europen Union Structurl Funds Beef Production Series No. 20. Sntschi, D. E., J. Chiquette, R. Berthiume, R. Mrtineu, J. J. Mtte, A. F. Mustf nd C. L. Girrd. 2005. Effects of the forge to concentrte rtio on B-vitmin concentrtions in different ruminl frctions of diry cows. Cn. J. Anim. Sci. 85:389-399. Sntos, J. E. P., H. Men, J. T. Huber, nd M. Trzon. 2005. Effects of source of gossypol nd supplementl iron on plsm gossypol in Holstein steers. J. Diry Sci. 88:3563-3574. 68 November 12-13 Grntville, PA
Sntos, J. E., M. Villsenor, P. H. Robinson, E. J. DePeters, nd C. A. Holmberg. 2003. Type of cottonseed nd level of gossypol in diets of lctting diry cows: Plsm gossypol, helth, nd reproductive performnce. J. Diry Sci. 86:892-905. Schwb, E. C., C. G. Schwb, C. L. Girrd, R. D. Shver, D. E. Putnm, nd N. L. Whitehouse. 2004. Effects of dietry forge nd non-fiber crbohydrte concentrtions on pprent B-vitmin synthesis in diry cows. J. Diry Sci. 87 (Suppl. 1):339 (Abstr.) Soch, M. T., S. M. Ensley, D. J. Tomlinson nd A. B. Johnson. 2003. Vribility of wter composition nd potentil impct on niml performnce. In: Proceedings from the Intermountin Nutrition Conference, Slt Lke City, UT. pp. 85 96. Suttle, N. F., 1975. An effect of soil ingestion on the utiliztion of dietry copper by sheep. J. Agri. Sci. 84:249-254. Tko, E., P. R. Ferkert nd Z. Uni. 2005. Chnges in chicken intestinl zinc exporter mrna expression nd smll intestinl functionlity following intr-mniotic zinc-methionine dministrtion. J. Nutr. Biochem. 16:339 346. Tiffny, M. E. nd J. W. Spers. 2005. Differentil response to dietry coblt in finishing steers fed corn- versus brley-bsed diets. J. Anim. Sci. 83:2580 2589. Underwood, E. J. nd N. F. Suttle. 1999. Mngnese. Pges 397 to 420 in The Minerl Nutrition of Livestock, 3rd Edition. CABI Publishing, Oxon, UK. pp 397 420. Wedekind, K. J., A. E. Hortin nd D. H. Bker. 1992. Methodology for ssessing zinc biovilbility: Efficcy estimtes for zinc-methionine, zinc sulfte nd zinc oxide. J. Anim. Sci. 70:178 187. Weiss, W. P. nd M. T. Soch. Dietry mngnese for dry nd lctting Holstein cows. J. Diry Sci. 88:2517 2523. 2008 Penn Stte Diry Cttle Nutrition Workshop 69
Tble 1. Exmple of NRC (2001) trce minerl requirements of cows in different stges of the lifecycle Animl Description Dry Cow Prefresh Cow b Entering 1 st Entering 2 nd Fresh Cow c Lctting Cow d lcttion lcttion Milk lb/d - - - 55 77 77 99 120 DMI, lb/d 31.7 23.4 30.2 29.7 34.3 51.9 59.2 66 Trce Minerl, ppm DM Coblt 0.11 0.11 0.11 0.11 0.11 0.11 0.11 0.11 Copper e 12 16 13 16 16 11 11 11 Iodine f 0.4 0.4 0.4 0.88 0.77 0.50 0.44 0.40 Iron 13 26 13 19 22 15 17 18 Mngnese 16 22 18 21 21 14 13 13 Selenium 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 Zinc 21 30 22 65 73 48 52 55 Holstein cow: BW, with conceptus 1609 lb, mture BW without conceptus 1499 lb, body condition score (BCS) = 3.3, 57 mos. of ge, 240 d pregnnt, clf weight = 99 lb, gining 1.5 lb with conceptus. b Holstein cow: 270 dys pregnnt, mture BW 1499 lb, BCS = 3.3, Entering 1 st lcttion, BW 1378 lb with conceptus gining 2.1 lb with conceptus; Entering 2 nd lcttion or greter, BW 1656 lb with conceptus. c Holstein cow: BW 1499 lb, mture BW 1499 lb, BCS = 3.3, 58 mos. of ge, milk ft = 3.5%, milk true protein = 3.0%, milk lctose = 4.8%, dys in milk = 11. d Holstein cow: BW 1499 lb, mture BW 1499 lb, BCS = 3.0, 65 mos. of ge, milk ft = 3.5%, milk true protein = 3.0%, milk lctose = 4.8%, dys in milk = 90. e High dietry molybdenum, sulfur, nd iron cn interfere with copper bsorption, incresing the requirement. f Diets high in goitrogenic substnces or nitrtes increse the iodine requirement. Tble 2. Effect of dietry mngnese on reproductive performnce of beef heifers (Hnsen et l., 2006) Item Supplementl Mngnese b, mg/kg 0 10 30 50 Estrus fter PGF 2αc, % 40 40 47 50 1 st service conception rte, % 45 40 47 60 Overll pregnncy rte d, % 60 50 67 75 Heifers strted the tril t 10 months of ge; Control diet contined 15.8 mg/kg Mn. b Supplied by Mn sulfte. c Response to prostglndin ws bsed upon two doses of prostglndin given t 13 mos of ge. d Rectl plption nd/or ultrsound t d 196 of the study. 70 November 12-13 Grntville, PA
Tble 3. Effect of trce minerl level nd source on reproductive performnce (Nocek et l., 2006) Item Tretments 75Z 100S 100Z Z/S Lcttion One b Dys to fi rst estrus 56 z 54 z 54 z 47 y Services/conception 2.3 2.4 2.2 1.9 Dys open 120 118 115 104 Lcttion Two b Dys to fi rst estrus 57 z 56 z 56 z 50 y First service conception rte, % 31.7 yz 29.6 y 33.5 yz 36.9 z Services/conception 2.6 2.5 2.7 2.2 Dys open 129 132 135 116 Pregnnt by 159 d, % 60.7 y 61.4 y 61.0 y 70.6 z 75Z nd 100Z tretments: Zn, Mn, Cu nd Co supplied ZINPRO ZnMet, MANPRO MnMet, CuPLEX CuLys nd COPRO Co glucoheptonte t 75 nd 100% of NRC (2001) requirements for erly lcttion cows; 100S tretment: Zn, Mn, Cu nd Co supplied by ZnSO 4, MnSO 4, CuSO 4 nd CoSO 4 t 100% of NRC (2001) requirements; Z/S tretment: Zn, Mn, Cu nd Co supplied by 4-Plex nd ZnSO 4, MnSO 4, CuSO 4 nd CoSO 4 t Zinpro Corportion recommendtions. Cows received tretments beginning in the dry period through lcttion 1, dry period through 200 d in lcttion 2. b For lcttion 1, includes only cows which completed lcttion 1 nd begn lcttion 2. For lcttion 2, includes only cows which completed 200 d in lcttion 2 nd were not designted s do not breed. yz LS mens lcking common superscript letter differ, P < 0.05. Tble 4. Coblt (Co) blnce of erly lcttion diry cows fed vrying mounts of Co (Kincid et l., 2003) Mesurement Dietry Tretments Low Coblt Medium Coblt High Coblt Coblt intke, mg/d 8.8 15.6 29.9 Milk coblt output, mg/d 3.3 3.1 3.3 Absorbed coblt t 2% effi ciency, mg/d 0.18 0.31 0.60 Absorbed coblt minus milk coblt, mg/d -3.1-2.8-2.7 Absorption effi ciency needed to = output, % 37 20 11 Low Co diet supplied 8.8 mg Co/d; medium Co diet, 15.6 mg Co/d; nd high Co diet, 29.9 mg Co/d. Additionl Co supplied by COPRO Co glucoheptonte. 2008 Penn Stte Diry Cttle Nutrition Workshop 71
Tble 5. Effect of coblt (Co) supplementtion nd grin source on ruminl vitmin B 12 concentrtion of fi nishing steers (Tiffny nd Spers, 2005) Item Added Co, mg/kg DM 0 0.05 0.15 Overll ruminl B 12b, pmol/ml 1.35 1.40 2.28 Corn bsed diets, ruminl B 12, pmol/ml 1.37 1.70 3.37 Brley bsed diets, ruminl B 12, pmol/ml 1.34 1.10 1.18 Added in the form of Co crbonte. Corn-bsed diet contined 0.04 ppm Co nd the brley bsed diet contined 0.02 ppm Co. b Grin source effect, P < 0.05; Level effect, 0.05 vs. 0.15 mg Co/kg DM, P < 0.05. Tble 6. Iron (Fe), zinc (Zn), copper (Cu) nd mngnese (Mn) content of selected feedstuffs Ingredient Fe, ppm DM Zn, ppm DM Cu, ppm DM Mn, ppm DM Avg Rnge Avg Rnge Avg Rnge Avg Rnge Alflf hy 273 96 822 26 19 45 9 6 19 63 23 169 Alflf silge 321 116 866 46 20 368 9 5 20 54 34 81 Almond hulls 222 74 709 15 7 30 3 1 15 18 11 35 Beet pulp, dry 290 204 447 29 21 43 2 0 6 52 43 66 Beet pulp, wet 262 183 324 29 18 37 4 1 7 58 41 94 Brewers grin, dry 123 103 154 94 78 161 17 15 21 49 43 71 Brewers grin, wet 138 108 163 88 75 105 11 7 18 49 46 56 Cnol mel 230 203 295 61 56 65 4 3 5 58 56 60 Citrus pulp, wet 61 46 79 8 6 11 3 2 4 6 5 13 Corn gluten feed 122 80 152 56 46 76 4 3 5 19 14 27 Corn silge 138 51 384 23 13 52 4 2 11 32 14 64 Distillers grin, dried 176 141 217 53 50 55 2 0 6 39 33 45 Grss silge (Dutch) 402 110 1400 41 20 74 8 5 12 113 30 195 Hominy feed 111 75 182 45 33 53 3 1 4 15 11 22 Molsses 171 123 277 18 4 77 5 2 13 80 22 121 Ot, brley silge - - 25 17 31 25 5 49 52 32 64 Rice brn 116 74 266 57 51 61 4 1 9 194 172 219 Sffl ower mel 308 258 414 112 76 346 26 20 46 80 27 510 Soy hulls 523 145 847 38 15 44 7 4 9 22 11 43 Whet mill run 187 58 433 70 22 82 23 2 153 117 34-151 Adpted from DePeters et l., 2000 nd Olson et l., 2002 72 November 12-13 Grntville, PA
Tble 7. Vrition in minerl content of 3651 wter smples nd mount of minerl supplied by wter s percent of minerl requirements (Soch et l., 2003) Minerl Minerl Content of Wter, ppm % of NRC (2001) Requirements Supplied By Wter Men Mximum Men Mximum Clcium 65 590 5.0 45.3 Mgnesium 24 682 5.0 141.0 Chloride 59 727 9.1 111.8 Potssium 4 33 0.2 1.3 Sodium 46 1556 9.0 303.3 Sulfur 27 1197 5.6 248.2 Copper 0.07 11.00 2.8 443.4 Iron 0.79 123.00 19.7 3065.0 Mngnese 0.17 12.70 5.5 413.6 NRC (2001) requirements for lctting cow, BW 1499 lb, 0 d pregnnt, body condition score 3, 30 dys in milk, third lcttion, 13 month clving intervl, 110 lb milk/d, 3.8% ft, 3.0% true protein, 68 F, no grzing. Tble 8. Impct of vrying sulfur nd molybdenum concentrtion on bsorption coeffi cient of copper (NRC 2001) Sulfur, % DM Molybdenum, ppm DM Absorption Coeffi cient for Dietry Copper 0.20 1 0.046 0.40 1 0.031 0.60 1 0.021 0.25 0.5 0.043 0.25 1 0.042 0.25 2 0.039 0.25 5 0.031 0.25 10 0.022 0.25 20 0.010 0.25 100 0.003 2008 Penn Stte Diry Cttle Nutrition Workshop 73
Tble 9. Summry of diry trils evluting Performnce Minerls, iso trils (Kellogg et l., 2003; Ferguson et l., 2004; Kincid nd Soch, 2004) Mesurement n b Control Performnce Minerls c P = d Milk, lb/d 6 79.7 81.4 0.07 ECM e, lb/d 6 80.6 82.6 0.01 3.5% FCM f, lb/d 6 80.8 82.7 0.02 Ft, lb/d 6 2.86 2.92 0.04 Protein, lb/d 6 2.43 2.50 0.01 Solids (ft+protein), lb/d 6 5.29 5.43 0.01 Ft, % 6 3.61 3.62 0.82 Protein, % 6 3.06 3.09 0.33 SCC, 1000s/mL 4 256 267 0.64 Dys to fi rst service 4 71 66 0.07 Dys open 5 143 130 0.10 Services/conception 4 2.7 2.4 0.18 Cows pregnnt t 150 d postprtum, % 2 56.5 69.5 0.07 4-Plex, Zinpro Corportion, Eden Pririe, MN. b Number of trils in which dt were vilble on selected prmeter, verges presented s LS mens. c In two studies, the control diet provided 360 mg Zn/hd/d from zinc methionine; in fi ve studies, both diets contined equivlent mounts of Zn, Mn, Cu nd Co; in one study, both diets supplied equivlent mounts of Zn, Mn nd Cu, but the 4-Plex diet supplied n dditionl 13 mg Co/hd/d. d Model for sttisticl nlysis included effect of tril (block) nd tretment within tril (experimentl unit). e Energy-corrected milk, 3.5% ft nd 3.0% true protein. f Ft-corrected milk, 3.5% ft. Tble 10. Trce minerl recommendtions for dry nd erly, mid nd lte lcttion cows Trce Minerl Dry or Erly Lcttion Cows Supplementl, ppm DM Mid to Lte Lcttion Cows Performnce / Orgnic Zinc 75 to 85 55 to 65 360 mg Mngnese 55 to 75 40 to 55 200 mg Copper 14 to 16 10 to 12 125 mg Coblt 0.8 to 1.2 0.6 to 0.9 25 mg Iodine 0.9 to 1.1 0.7 to 0.8 100% (EDDI) Iron 0 to 10 0 to 10 0 Selenium 0.3 0.3 Holstein cow, clving BW, 1400 lb; pek milk, 110 lb; 8% decline in milk yield fter pek, pek milk 2 months fter clving, 365 d milk yield, 30,714 lb; NRC predicted DMI; defult environmentl conditions; conception dte, 5 months fter clving; verge milk ft, 3.5%; verge dily gin with conceptus, 0.4 lb/d. 74 November 12-13 Grntville, PA
Zinc Mngnese Copper Iron 80 60 ppm 40 20 0-2 1 3 5 7 9 11 13 Month Reltive to Clving Figure 1. Effect of lcttion nd gesttion on Zn, Mn, Cu nd Fe requirements (ppm DM bsis). Requirements bsed upon Holstein cow, clving BW, 1400 lb; pek milk, 110 lb/d; pek milk two months fter clving; 365 dy milk yield, 30,174 lb; NRC predicted DMI; defult environmentl conditions; conception dte fi ve months fter clving; verge milk ft, 3.5%; verge dily gin with conceptus, 0.4 kg. Cows re dried off t 12 months postclving. Figure 2. The reltionship between Mn intke nd pprent Mn blnce in dry nd lctting diry cows. Ech point represents cow or cow-period nd re djusted for rndom tril effects. The circles represent lctting cows nd the tringles represent dry cows. The red line represents the reltionship between Mn intke nd Mn blnce. Anlysis indictes tht Mn blnce equls zero when Mn intke equls 580 mg/d (Weiss nd Soch, 2005). 2008 Penn Stte Diry Cttle Nutrition Workshop 75
Figure 3. Effect of prity nd level of coblt supplementtion on 3.5% FCM yield (Kincid et l., 2003). During lcttion, mounts of Co/d were low Co diet, 8.8 mg; medium Co diet, 15.6 mg; nd high Co diet, 29.9 mg. Additionl Co supplied by CoPRO Co glucoheptonte. Tretment by prity by week interction (P < 0.01). 250 200 177 z 206 z ZnSO 4 ZnMet b Reltive Vlue 150 100 100 w 117 x 100 y 100 y 50 0 Amino Acid Soy Isolte Corn-SBM Figure 4. Biovilbility of zinc (Zn) from Zn methionine (Met; Zinpro Corportion, Eden Pririe, MN) reltive to Zn from Zn sulfte (Wedekind et l., 1992). Biovilbility estimted using multiple regression nlyses of totl tibi Zn in chicks; zinc sulfte set to 100. wx Mens lcking common superscript letter differ (P < 0.05). yz Within diet type, mens lcking common superscript letter differ (P < 0.01). 76 November 12-13 Grntville, PA