Effect of antibiotic growth promoters on broiler performance, intestinal growth parameters, and quantitative morphology.

The effects of addition of bacitracin methylene disalicylate (BMD) or virginiamycin (VM) to a corn-soybean meal diet on broiler performance and gastrointestinal tract (GIT) growth parameters and morphology were studied at various ages during growth and finishing. Male and female birds were killed at 1, 3, 5, or 7 wk of age for gross and histologic examination of the duodenum and ileum. Feeding either antibiotic increased BW and decreased intestinal length and weight at all times compared with control birds. However, intestinal length and weight decreases were greater in birds fed VM than BMD at 1 and 3 wk of age. The only change found in the duodenum resulting from dietary treatment was an increase in the number of villi per unit length in birds given VM but not BMD or control. In the ileum, the muscularis mucosa was thinner in birds given VM than in those fed the control diet. Chicks supplemented with VM had a smaller total villus area and shorter villus height and crypt depth in the ileum than birds fed the control diet or BMD. Physical changes in the intestine of birds given either antibiotic growth promoter, although not the same, resulted in improved performance.

Muraceins--muramyl peptides produced by Nocardia orientalis as angiotensin-converting enzyme inhibitors. I. Taxonomy, fermentation and biological properties.

Three muraceins , a family of muramyl peptides, were isolated from Nocardia orientalis as inhibitors of angiotensin-converting enzyme (ACE). Muracein A, the most potent inhibitor, inhibited ACE competitively with a Ki of 1.5 microM. Liver alcohol dehydrogenase and carboxypeptidase A, two other zinc-containing enzymes, were not inhibited at 150 microM. Inhibition of ACE could not be reversed by divalent cations.

Phenacein--an angiotensin-converting enzyme inhibitor produced by a streptomycete. I. Taxonomy, fermentation and biological properties.

Phanacein, 3,6-dihydroxy-1-phenazinecarboxylic acid, was a specific angiotensin-converting enzyme (ACE) inhibitor isolated from a member of the Streptomyces tanashiensis-zaomyceticus group. Phenacein acted as a pure competitive inhibitor with a Ki of 0.58 microM. ACE inhibition could be reversed by Zn++, but not by Co++, Ca++, or Mg++; therefore, phenacein may chelate the active site zinc of ACE. However, other zinc-containing enzymes were not inhibited at high phenacein concentrations. Phenacein exhibited weak activity against Gram-positive bacteria, but was not active against Candida sp. or Gram-negative organisms.

Interrelationship of dietary phosphorus, aluminum and iron on performance and tissue mineral composition in lambs.

A 76-d feeding trial was conducted with 24 wether lambs (31 kg, initially) to study the interrelationships among dietary P, Al and Fe. A 2 x 2 x 2 factorial arrangement of treatments included two concentrations of supplemental P (0 or .25%) with added P as NaH2PO4, two levels of supplemental Fe (0 or 760 ppm) with Fe added as ferric citrate and two levels of supplemental Al (0 or 1,450 ppm) with Al added as AlCl3 . 6H2O. The basal diet contained .17% P, 40 ppm Fe and 168 ppm Al. Phosphorus increased (P less than .01) feed consumption, but Fe (P less than .01), with added P improving and Fe or Al depressing gain. Additional P improved gain (P less than .05) and intake (P less than .01) in the presence of high Al and intake (P less than .05) when dietary Fe was high. Serum P was increased (P less than .01) by high dietary Fe and reduced (P less than .01) by Al. High dietary P increased (P less than .05) serum MG. High dietary Fe increased (P less than .01) hemoglobin and hematocrit and increased (P less than .01) Fe storage in liver, kidney, spleen and muscle but decreased (P less than .01) kidney Zn concentration. High dietary Al increased (P less than .01) liver Fe and kidney Zn levels but decreased kidney P and Mg (P less than .05) and bone ash and Mg (P less than .01). Based on these studies, additional dietary P appeared beneficial in overcoming the adverse effects of high dietary Al or Fe.

Statistical analysis of repeated measures data using SAS procedures.

Mixed linear models were developed by animal breeders to evaluate genetic potential of bulls. Application of mixed models has recently spread to all areas of research, spurred by availability of advanced computer software. Previously, mixed model analyses were implemented by adapting fixed-effect methods to models with random effects. This imposed limitations on applicability because the covariance structure was not modeled. This is the case with PROC GLM in the SAS System. Recent versions of the SAS System include PROC MIXED. This procedure implements random effects in the statistical model and permits modeling the covariance structure of the data. Thereby, PROC MIXED can compute efficient estimates of fixed effects and valid standard errors of the estimates. Modeling the covariance structure is especially important for analysis of repeated measures data because measurements taken close in time are potentially more highly correlated than those taken far apart in time.

Effects of high dietary manganese as manganese oxide or manganese carbonate in sheep.

Twenty-four crossbred Florida native wether lambs, 28 kg initially, were assigned randomly to a basal diet (31 ppm Mn dry matter basis) supplemented with either 0, 500, 1,000, 2,000 or 4,000 ppm Mn from feed grade MnO or 2,000, 4,000 or 8,000 ppm Mn from reagent grade MnCO3. There were three sheep/treatment, with ad libitum access to feed and tap water. After 84 d, all animals were slaughtered and tissues removed for analysis. Dietary Mn at the highest levels from either source reduced (P less than .05) average daily feed intake and average daily gain. Hemoglobin and hematocrit were not affected by dietary Mn. Manganese concentration in kidney, spleen, heart, skeletal muscle, bone, serum (P less than .01) and liver (P less than .05) increased as dietary Mn increased. Kidney P was reduced (P less than .05) as dietary Mn increased; however, no other tissue minerals were affected. At comparable levels of supplementation, sheep fed feed-grade MnO exhibited numerically greater tissue Mn concentration than did those fed reagent-grade MnCO3 and regression analysis indicated higher rates of tissue uptake in MnO-supplemented sheep. Reduced feed intake and gain and apparent Mn homeostatic failure in liver were the only observed effects that may have been related to Mn toxicosis.

Vanadium metabolism in sheep. II. Effect of dietary vanadium on performance, vanadium excretion and bone deposition in sheep.

Sixteen ram lambs were fed 0, 50 or 200 ppm supplemental vanadium daily as NH4VO3 for 90 d and coccygeal vertebrae were sampled at 0, 15, 30, 60 and 90 d after the imposition of dietary treatments. Vertebral vanadium content was elevated (P less than .05) after exposure to 200 ppm added vanadium in the diet of 15 d, but nonsignificant increases occurred thereafter. Increasing dietary vanadium increased bone ash vanadium concentration from .4 to 1.7 and 3.8 ppm in sheep fed 0, 50 and 200 ppm supplemental vanadium, respectively. In a balance study, urinary concentrations of the element also were related directly to dietary intake. A trend toward elevated urine volume with increased intake of vanadium was also observed.

Effects of time and dietary selenium concentration as sodium selenite on tissue selenium uptake by sheep.

Thirty crossbred wethers (60 kg avg initial wt) were used to study the time-dose response to dietary Se as sodium selenite (Na2SeO3). Sheep were fed a basal diet (.20 mg/kg Se, M basis) for 10 d; three wethers were killed and tissues were collected for controls. The remaining 27 sheep were assigned randomly to diets supplemented with either 3, 6 or 9 mg/kg Se (as-fed basis) from reagent grade Na2SeO3 and fed for 10, 20 or 30 d. Feed offered was restricted to 1,200 g daily and tap water was available ad libitum. Sheep were stunned and killed by exsanguination and liver, kidney, muscle, heart and spleen were removed and frozen for Se analysis. No toxic effects were noted as expressed by feed intake or hemoglobin concentration. Added dietary Se increased Se linearly (P less than .01) in liver, kidney, and serum. Selenium in liver, kidney and serum also increased (P less than .01) as time advanced. Serum, liver and kidney were more sensitive to dietary Se than were muscle, heart and spleen. Ten days appeared to be an adequate length of time for further Se bioassay studies of this nature. Reagent grade Na2SeO3 was nontoxic when fed to sheep for 30 d at levels up to 90 times the Se requirement.

Estimation of the relative biological availability of inorganic selenium sources for ruminants using tissue uptake of selenium.

An experiment was conducted to estimate the relative bioavailability of inorganic Se sources based on tissue Se deposition following supplementation at high dietary levels. Twenty-eight crossbred wethers averaging 50 kg initial weight were assigned randomly to seven treatments that were fed for 10 d. The basal diet contained .18 mg/kg Se (DM basis). Dietary Se was added at 0, 3, 6 or 9 mg/kg as reagent grade sodium selenite (Na2SeO3) and 6 mg/kg from either calcium selenite (CaSeO3), Na2SeO3 + fumed amorphous carrier or sodium selenate (Na2SeO4). There were four sheep per treatment group, housed in individual, raised pens with slatted floors. Daily feed intake was restricted to 1,200 g and tap water was available ad libitum. The basal diet was fed for a 10-d adjustment period, then sheep were fed experimental diets for 10 d. At the termination of the experiment, blood samples were taken; sheep were stunned and killed, and livers and kidneys were removed and frozen for Se analysis. There was a linear (P less than .001) uptake of Se in liver, kidney and serum. The CaSeO3 and Na2SeO4 sources resulted in greater (P less than .05) Se concentrations in liver and kidney than did Na2SeO3, but these differences were not significant when the analyzed dietary Se concentrations were used as a covariate in the statistical model. Based on linear and multiple linear regression slopes and average increases in serum, liver and kidney Se concentrations, estimated relative bioavailability values corrected for analyzed dietary concentration, were 100, 101, 90 and 133 for Na2SeO3, CaSeO3, Na2SeO3 + carrier and Na2SeO4, respectively.

Estimation of the relative bioavailability of manganese sources for sheep.

The relative biological availability of Mn in reagent-grade (RG) Mn sources was tested using 41 Rambouillet crossbred wether lambs in a completely randomized design. Lambs were fed a basal corn-soybean meal-cottonseed hull diet (37.6 ppm Mn, DM basis) or this basal diet supplemented with 0, 1,500, 3,000 or 4,500 ppm Mn from RG MnSO4.H20 or 3,000 ppm Mn from RG MnO, MnO2 and MnCO3. Feed intake was restricted to 1,000 g/hd daily during the 21-d experimental period. There was a decrease (P less than .01) in daily feed intake by sheep fed 4,500 ppm Mn from MnSO4. Liver, kidney and bone Mn concentrations increased (P less than .05) with MnSO4 supplementation. Liver was most responsive to dietary Mn, followed by kidney and bone. Based on multiple linear regression slopes for liver, kidney and bone Mn concentrations, relative bioavailability of Mn from MnO, MnO2 and MnCO3 averaged 57.7, 32.9 and 27.8%, compared with 100% for MnSO4.

Effects of dietary phosphorus, soil ingestion and dietary intake level on performance, phosphorus utilization and serum and alimentary tract mineral concentrations in lambs.

Two experiments were conducted with lambs fed concentrate-based diets to study the effects of dietary P and soil ingestion on performance, P utilization and mineral composition of serum and alimentary tract contents. In Exp. 1, 20 wether lambs were fed diets for 21 d in a 2 X 2 factorial arrangement of treatments with .2 or .3% total dietary P and O or 9% added Florida Ultisol (highly weathered soil with high P-fixation capacity) containing 4,600 and 6,400 mg/kg total Al and Fe, respectively. True P absorption increased (P less than .05) from 30 to 42% and from 37 to 54% when soil was added to the basal and high P diets, respectively. In Exp. 2, 24 wether lambs were assigned randomly to a 2 X 2 X 2 factorial arrangement of treatments. Lambs were fed during a 70-d period using diets described previously on either a restricted or an ad libitum basis. Soil increased Fe concentration in ruminal fluid (P less than .05) and ash percentage (P less than .001) in ruminal solids and feces. Aluminum concentration in ruminal solids and feces and Fe in ruminal solids were increased (P less than .001) by soil addition, whereas concentrations of Ca, Mg, P, Zn, Cu and Mn in ruminal solids and feces were decreased (P less than .01) by soil addition. There were time X P interactions on serum inorganic P (P less than .01) and Mg (P less than .05) concentrations. Although high in P-fixing capacity, soil fed to lambs in these experiments improved P utilization. Lambs appeared to be able to adapt to changes in intake of dietary minerals in soil, possibly through adaptation of ruminal microflora or a redistribution of body mineral pools.

Relative bioavailability of supplemental inorganic zinc sources for chicks.

Three experiments were conducted to investigate the relative bioavailability of reagent-grade (RG) and feed grade (FG) Zn sources for 1-d-old broiler chicks. In Exp. 1, 13 treatments included a basal corn-soybean meal diet (63 ppm Zn) or the basal diet supplemented with 400, 800, or 1,200 ppm Zn from RG sulfate, basic carbonate, oxide, or metal and fed for 20 d. Using multiple regression slope ratios with Zn sulfate set at 100%, bioavailability estimates were 78, 77, and 46% for carbonate, oxide, and metal, respectively. In Exp. 2, chicks were allotted randomly to 16 treatments that included a basal corn-soybean meal diet (75 ppm Zn) or basal diet supplemented with 300, 600, or 900 ppm Zn as either RG sulfate, FG sulfate-A, FG sulfate-B, FG oxide-A, or FG oxide-B and fed for 21 d. Multiple linear regression slope ratios gave relative estimates of 99, 81, 78, and 54% for sulfate-A, sulfate-B, oxide-A, and oxide-B sources, respectively, with RG sulfate set at 100%. In Exp. 3, chicks were fed a basal corn-soybean meal diet (35 ppm Zn) or the basal diet supplemented with 40, 80, or 120 ppm Zn from RG Zn sulfate, FG sulfate, or FG oxide and fed for 20 d. Multiple regression slope ratios with RG sulfate set at 100% gave relative bioavailability estimates of 94 and 74% for the FG sulfate and oxide, respectively. Bioavailability estimates were similar when Zn was supplemented to diets at high or low concentrations.

Estimation of the relative bioavailability of inorganic copper sources for chicks using tissue uptake of copper.

An experiment was conducted with 208 day-old male Cobb feather-sexed chicks to study tissue accumulation of Cu as an estimate of biological availability of inorganic Cu sources for chicks. Chicks were allotted randomly to dietary treatments that included an unsupplemented basal corn-soybean meal diet (11.1 mg/kg Cu, DM basis) or this basal diet supplemented with 150, 300 or 450 mg/kg Cu either as reagent-grade acetate or feed grade oxide, carbonate or sulfate. Chicks were housed in batteries and allowed ad libitum access to feed and tap water for 21 d. Liver Cu was not affected by dietary Cu from the oxide source, but it increased (P less than .001) with increasing dietary Cu from all other sources. Bone Cu was lower (P less than .05) in chicks fed 150 mg/kg Cu compared to other dietary levels of Cu but was not influenced (P greater than .10) by Cu source. Using the slope-ratio technique from regression of log liver Cu on mean daily Cu intake with Cu from acetate set at 100%, the relative biological availability values were estimated to be 88.5 and 54.3% for sulfate and carbonate, respectively, and oxide was essentially unavailable.

Vanadium metabolism in sheep. III. Influence of dietary vanadium on kinetics of 48V administered orally or intravenously and comparison of compartmental and graphical models.

Radiotracer techniques were used to investigate the influence of dietary stable V on the excretion, distribution and blood clearance kinetics of 48V in 14 rams averaging 58 kg body weight. Rams were fed a basal diet with added levels of 0, 50 or 200 mg/kg V as NH4 VO3 for 25 wk before either oral or iv administration of the isotope. A three-compartment model was determined by graphical logarithmic analysis of blood disappearance data from iv-dosed rams and compared with a simultaneous multicompartment model, which made it possible to ascribe physiological processes to the components of the graphical model. The principal route of excretion of 48V administered iv was via urine, whereas the isotope given orally was excreted almost entirely by way of feces, resulting in low tissue and urinary 48V levels. Increasing dietary V increased (P less than .05) the percentage of dose excreted in urine regardless of dosing route, but dietary V had no effect on 48V excreted in feces. Stable dietary V had no effect on blood clearance rates of orally or iv-dosed rams. Dietary V addition decreased 48V concentration in kidney (P less than .01), liver, spleen, testes and muscle (P less than .05) of iv-dosed rams, but had no effect in rams dosed orally. Kidney, bone, liver and spleen retained the highest levels of 48V activity 144 h after dosing. Dietary V appeared to have a minimal effect on V kinetics in rams.

Estimation of relative bioavailability of nutrients using SAS procedures.

The General Linear Models procedure (PROC GLM) in SAS/STAT software can be programmed to perform the standard statistical analyses used for relative bioavailability studies. The first steps are validity checks to test for statistical validity (linearity), fundamental validity (intersection of regression lines at 0 supplemental level), and equality of the basal diet mean to the point of intersection. The CLASS variable capabilities of PROC GLM can be exploited to expedite these tests. After the validity checks, the GLM procedure can be used to obtain parameter estimates for calculation of relative bioavailability. Optional output provides an inverse matrix to calculate standard errors of slopes and slope ratios. Logarithmic and other transformations of the dependent variable to reduce variance heterogeneity or achieve linearity for subsequent calculation of appropriate bioavailability values also can be accomplished within the SAS System. When nonlinear regression models are more appropriate than linear models, the NLIN procedure can be used.

Influence of dietary lead and calcium on tissue lead accumulation and depletion, lead metabolism and tissue mineral composition in sheep.

Two experiments were conducted to study the metabolism and tissue accumulation and depletion of dietary Pb in sheep. In Exp. 1, a feeding trial, 33 wethers, 56 kg initially, were assigned randomly to two dietary treatments: .25% Ca plus 1,000 ppm Pb or .50% Ca plus 1,000 ppm Pb. Supplemental Ca and Pb were supplied as reagent grade calcium carbonate or reagent grade lead acetate. The experiment was divided into two phases of 75 and 180 d; during the first phase, diets contained 1,000 ppm supplemental Pb and during the second phase, diets contained 3 ppm Pb. Calcium level remained constant within treatments throughout both phases. Sheep were slaughtered at various intervals during both phases and tissue samples taken. Lead increased in all tissues during the accumulation period and decreased during the depletion period; however, kidney was the only tissue in which Pb concentration declined to control values by 180 d. Dietary Ca reduced (P less than .05) the concentration of Pb deposited in liver, but not in other tissues. Interactions of dietary Ca and Pb on tissue concentration of various minerals occurred. In Exp. 2, a balance trial, 27 wethers, 53 kg initially, were allotted randomly to four treatments in a 2 X 2 factorial arrangement. Diets contained either 0 or 1,000 ppm supplemental Pb as reagent grade lead acetate and .25 or .50% total Ca with supplemental Ca from calcium carbonate. Increasing dietary Pb increased (P less than .05) percentage of Pb retained and increased (P less than .01) whole blood Pb concentration (1.0 vs 1.42 micrograms/ml).

Vanadium metabolism in sheep. I. Comparative and acute toxicity of vanadium compounds in sheep.

Twelve Florida native wethers were given ammonium metavandate, calcium orthovanadate and calcium pyrovanadate by capsule in a study to examine the toxicity of the compounds. The initial daily dosage of 100 mg elemental vanadium was increased by 50 mg at 2-d intervals for an assessment not only of the toxic effects, but also to determined the amount that caused a decline in feed intake to 25% of that of control animals. The initial decline in feed intake was observed at 400 to 500 mg vanadium/d (9.6 to 12 mg/kg body weight, 310 to 350 ppm); a rapid decline in feed intake was accompanied by diarrhea. One sheep fed 550 mg vanadium as calcium orthovanadate died 3 d after dosing. One animal on each of the other three treatments was killed and necropsied for immediate comparison. Extensive mucosal hemorrhage of the small intestine and diffuse or petechial subcapsular hemorrhages of the kidneys were observed for sheep fed all compounds. The three vanadium compounds appeared to be similar in toxicity, as determined by abrupt declines in feed intake and pathological changes of the intestine and kidney. For a determination of acute toxicosis, three sheep were given 40 mg/kg body weight of vanadium as NH4VO3 in gelatin capsules and two sheep were included as controls. Two of the treated animals died within 80 h after administration and the other three were killed at 96 h. Vanadium content of kidney, liver, bone, spleen, lung and muscle was elevated by treatment.

Effect of dietary zinc source and method of oral administration on performance and tissue trace mineral concentration of broiler chicks.

Two experiments were conducted with chicks to examine the effect of high dietary levels of soluble sources of Zn on tissue Zn, Cu, and Fe concentrations as influenced by two methods of oral Zn administration from 14 to 21 d of age. Treatments included the basal diet (62 ppm Zn), basal diet supplemented with 1,000 ppm Zn from Zn sulfate, acetate, or chloride fed continuously, or basal diet plus crop intubation with a single oral dose of water (control) or 1,000 ppm Zn dietary equivalent from the sources based on feed intake from the previous day. In Exp. 2, crop-intubated doses were administered daily from 14 to 21 d of age. In Exp. 1, chicks given Zn by gavage decreased (P < .0001) feed intake at 24 h after oral dose compared with chicks fed either the control or high-Zn diets. After the gavage dosing stopped, feed intake was similar among treatments. Bone Zn was increased (P < .0001) by Zn source and was greater at 24 than at 168 h after dosing by gavage. In chicks given a single gavage dose of Zn, liver and kidney Zn measured at 24 h after oral dosing was greater (P < .0001) than at 168 h. In birds given a single oral dose of Zn, time x Zn source interactions were observed in pancreas (P < .0001), mucosal cells (P < .01), and remaining intestinal tract segments (P < .001). In Exp. 2, greater bone, pancreas, kidney (P < .0001), and liver (P < .001) Zn accumulations were observed in chicks given daily gavage doses of Zn compared with those fed Zn in diets. Zinc from the four sources was absorbed and stored in tissues to a similar extent.

Chemical characteristics and relative bioavailability of supplemental organic zinc sources for poultry and ruminants.

Eight commercially available organic Zn products and reagent-grade ZnSO4 x 7H2O (Zn Sulf) were evaluated by polarographic analysis, and solubility in .1 M K2HPO4-KH2PO4 buffer (pH 5), .2 M HCl-KCl buffer (pH 2), and deionized water. Fractions from these solubility tests were evaluated by gel filtration chromatography for structural integrity. Degree of chelation was generally positively related to chelation effectiveness determined by polarography. The organic sources were Zn methionine complex A (Zn MetA), Zn methionine complex B (Zn MetB), Zn polysaccharide complex (Zn Poly), Zn lysine complex (Zn Lys), Zn amino acid chelate (Zn AA), Zn proteinate A (Zn ProA), Zn proteinate B (Zn ProB), and Zn proteinate C (Zn ProC). Three experiments were conducted to estimate the relative bioavailability of Zn from the organic Zn supplements for chicks and lambs when added at high dietary levels to practical diets. Bone Zn concentration increased (P < .001) as dietary Zn increased in both experiments. When Zn Sulf was assigned a value of 100% as the standard, multiple linear regression slope ratios of bone Zn from chicks fed 3 wk regressed on dietary Zn intake gave estimated relative bioavailability values of 83 +/- 14.6 and 139 +/- 16.9 for Zn AA and Zn ProA, respectively, in Exp. 1 and 94 +/- 11.6, 99 +/- 8.8, and 108 +/- 11.4 for Zn Poly, Zn ProB, and Zn ProC, respectively, in Exp. 2. In Exp. 3, 42 lambs were fed diets containing Zn Sulf, Zn ProA, Zn AA, or Zn MetB for 21 d. Based on multiple linear regression slope ratios of liver, kidney, and pancreas Zn and liver metallothionein concentrations on added dietary Zn, bioavailability estimates relative to 100% for Zn Sulf were 130, 110, and 113 for Zn ProA, Zn AA, and Zn MetB, respectively. Except for Zn ProA, which was greater, the organic Zn supplements had bioavailability values similar to that of Zn Sulf for chicks and lambs. Bioavailability of organic Zn products was inversely related to solubility of Zn in pH 5 buffer in chicks (r2 = .91) and pH 2 buffer in lambs (r2 = .91), but not to an estimate of degree of chelation.

Chemical characteristics and relative bioavailability of supplemental organic copper sources for poultry.

Five commercially available organic Cu products and reagent-grade CuSO4 x 5H2O (Cu Sulf) were evaluated by polarographic analysis and solubility in 0.1 M K2HPO4-KH2PO4 buffer (pH 5), 0.2 M HCl-KCl buffer (pH 2), or deionized water. Fractions from these solubility tests were evaluated by gel filtration chromatography for structural integrity. The organic sources were Cu lysine complex (Cu Lys), Cu amino acid chelate (Cu AA), Cu proteinate A (Cu ProA), Cu proteinate B (Cu ProB), and Cu proteinate C (Cu ProC). Separation of peaks in the chromatograms for the soluble Cu fraction from deionized water indicated that 77, 31, 69, 94, and 16% of the Cu remained chelated for the above sources, respectively. Two experiments were conducted to estimate the relative bioavailability of Cu from the organic Cu supplements for chicks when added at high dietary concentrations to practical corn-soybean meal diets. Liver Cu concentration increased (P < 0.0001) as dietary Cu increased in both experiments. When Cu Sulf was assigned a value of 100% as the standard, linear regression slope ratios of log10 liver Cu concentration regressed on added dietary Cu concentration gave estimated relative bioavailability values of 124 +/- 5.1, 122 +/- 5.3, and 111 +/- 6.0 for Cu Lys, Cu AA, and Cu ProC, respectively, in Exp. 1. The bioavailability estimates for Cu Lys and Cu AA were greater (P < 0.05) than that for Cu Sulf. Values in Exp. 2 were 111 +/- 7.6, 109 +/- 8.4, and 105 +/- 7.5 for Cu Lys, Cu ProA, and Cu ProB, respectively, and all sources were similar in value for chicks. Solubility of Cu in pH 2 buffer provided the best prediction of bioavailability (r2 = 0.924). Other indicators of chelation integrity and solubility had little value as predictors of bioavailability (r2 < or = 0.445).