Biomedical subjects

R C Littell

Publications and source records attributed to R C Littell.

At least 19 recordsLinked to original sources

PubMed2006

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.

Animals↗

PubMed2006

Appropriate statistical methods to compare dose responses of methionine sources.

Two sources of methionine (Met) activity are frequently used in commercial feed formulation: DL-2-hydroxy-4-(methylthio) butanoic acid (HMTBA), most commonly available as an 88% solution with 12% water; and DL-methionine (DLM, 99% powder). Despite the fact that both compounds have been in commercial use for over 50 yr, controversy and confusion remain with respect to their relative bioefficacy (RBE). This paper presents a review of the use of a nonlinear common plateau asymptotic regression technique (NLCPAR) that has been used to compare the 2 Met sources with particular emphasis on the validity of the basic assumptions of that model. The thesis of this paper is that the controversy is due, at least in part, to the misapplication of this regression technique to estimate the RBE of HMTBA and DLM. The NLCPAR model is a bioassay with the key dependent assumptions that HMTBA is a dilution of DLM, and that each follows dose-response curves of the same form and approach a common plateau. Because both provide Met activity, it may be considered reasonable to accept these assumptions; however, specifically testing them demonstrated that the assumption of a common dose-response is not supported by data. The common plateau assumption was tested with an alternative approach of fitting nonlinear separate plateaus asymptotic regression (NLSPAR) to a set of 13 published broiler studies in which the NLCPAR model had been used to estimate RBE of HMTBA and DLM. The hypothesis of a common plateau was rejected (P < 0.01), meaning that the conclusion that HMTBA had lower bioefficacy than DLM based on the NLCPAR methodology was not valid. An example using published data demonstrated that the NLSPAR model was a significantly better fit than the NLCPAR model, and showed that HMTBA and DLM followed different dose responses. Consequently, there was no single value for RBE for the entire dose range; rather, the RBE of the 2 compounds varied with use level. The evidence presented here indicates that separate plateau models should be used when comparing these 2 products. These more valid models can then be used for predictions of differences between HMTBA and DLM at levels of expected use.

Animal Feed↗

PubMed2005

Effects of arsenic species and concentrations on arsenic accumulation by different fern species in a hydroponic system.

Two hydroponic experiments were conducted to evaluate factors affecting plant arsenic (As) hyperaccumulation. In the first experiment; two As hyperaccumulators (Pteris vittata and P. cretica mayii) were exposed to 1 and 10 mg L(-1) arsenite (AsIII) and monomethyl arsenic acid (MMA) for 4 wk. Total As concentrations in plants (fronds and roots) and solution were determined In the second experiment P. vittata and Nephrolepis exaltata (a non-As hyperaccumulator) were exposed to 5 mgL(-1) arsenate (AsV) and 20 mgL(-1) AsIIIfor 1 and 15 d. Total As and AsIII concentrations in plants were determined Compared to P. cretica mayii, P. vittata was more efficient in arsenic accumulation (1075-1666 vs. 249-627mg kg(-1) As in the fronds) partially because it is more efficient in As translocation. As translocation factor (As concentration ratio in fronds to roots) was 3.0-5.6 for P. vittata compared to 0.1 to 4.8 for P. cretica. Compared to N. exaltata, P. vittata was significantly more efficient in arsenic accumulation (38-542 vs. 4.8-71 mg kg(-1) As in thefronds) as well asAs translocation (1.3-5.6 vs. 0.2-0.5). In addition, P. vittata was much more efficient in As reduction from AsV to AsIII (83-84 vs. 13-24% AsIII in the fronds). Little As reduction occurred after 1-d exposure to AsV in both species indicates that As reduction was not instantaneous even in an As hyperaccumulator. Our data were consistent with the hypothesis that both As translocation and As reduction are important for plant As hyperaccumulation.

Arsenates↗

PubMed2005

Effect of fibrolytic enzymes on the fermentation characteristics, aerobic stability, and digestibility of bermudagrass silage.

The aim of this study was to determine if the nutritive value and aerobic stability of bermudagrass (Cynodon dactylon) silage could be improved by addition of proprietary, exogenous cellulase/hemicellulase enzyme preparations at ensiling. A 5-wk regrowth of Tifton 85 bermudagrass was conserved without treatment (control) or after treatment with exogenous fibrolytic enzymes including Promote NET (Pr), Biocellulase X-20 (X20), Biocellulase A-20 (A20), and Enzyme CT. The respective enzymes were applied at half the recommended rate, the recommended rate, or twice the recommended rate corresponding to 0.65, 1.3, and 2.6 g/kg of DM, 7.3, 14.5, and 29 mg/kg of DM, at 7.3, 14.4, and 29 mg/kg of DM, and 89, 178, and 356 mg/kg of DM, for Pr, X20, A20, and CT, respectively. The enzymes were sprayed on the bermudagrass at ensiling (not added at feeding as suggested by the manufacturers) to test the objectives of the study. Six 1-kg replicates of chopped (5 cm) forage were ensiled for 145 d in 2.8-L mini silos. Three silos per treatment were used for chemical analysis and 3 for aerobic stability monitoring. The silage juice was analyzed for organic acids, pH, water-soluble carbohydrates (WSC), ammonia-N, and soluble N. Freeze-dried samples were analyzed for crude protein (CP), neutral detergent fiber (NDF), and acid detergent fiber (ADF). In vitro digestibility of DM (IVDMD), NDF (IVNDFD), and ADF (IVADFD) were determined after digesting the silages in buffered rumen fluid for 6 or 48 h in 2 ANKOM(II) Daisy Incubators. Compared with the other silages, those treated with Pr had lower DM losses, and lower pH and ammonia-N concentration than control silages. Residual WSC concentration was greater in Pr- and CT-treated silages than in control silages and greater in Pr-treated silages than CT-treated silages. Compared with control silages, NDF concentration was lower in silages treated with Pr, X20, and CT, and ADF concentration was lower in silages treated with Pr, X20, and A20. Nevertheless, Pr-treated silages contained lower ADF and NDF concentrations than silages treated with the other enzymes. Enzyme-treated silages contained less acetic acid than control silages, and Pr-treated silages had the lowest concentrations of acetic acid. Aerobic stability was increased by enzyme treatment but microbial counts were not affected. The 6-h IVDMD was increased by treatment with Pr and A20, however only Pr increased the IVDMD and IVNDFD at 48 h. The 48-h IVADFD was also increased by treatment with Pr, CT, and A20. These results show that when applied at ensiling, certain fibrolytic enzymes (particularly Promote) can improve the digestibility, fermentation, and aerobic stability of bermudagrass silage.

Aerobiosis↗

PubMed2005

Performance of lactating dairy cows managed on pasture-based or in freestall barn-feeding systems.

The objective was to compare productive and metabolic responses of lactating dairy cows managed on 2 pasture-based systems using a concentrate supplement (n = 16) with those of a freestall housing system (n = 24). In a 259-d experiment, 3 multiparous Holstein cows were assigned at calving to each of 4 replicates of 2 pasture systems. For system 1, winter pastures were a mixture of rye, ryegrass, and crimson and red clover; summer pastures were pearl millet. Pasture system 2 included a rye-ryegrass mixture during winter and bermudagrass during summer. Pregraze herbage mass averaged 2.3 and 3.6 Mg/ha for winter and summer pastures, respectively; however, during August through September, pearl millet pregraze mass was reduced to about 1 Mg/ha. Daily dry matter intake by cows on pasture averaged 24.7 kg/d in winter and 19.0 kg/d in summer, of which 55% was from pasture; that of cows in confined-housing averaged 23.6 kg/d. Cows in confinement produced 19% more milk (29.8 vs. 25.1 kg/d) than those on pasture systems. Differences in concentration of milk fat, protein, or urea N were not detected among treatment groups. Grazing cows lost more body weight than confined cows (113 vs. 58 kg) and had lower concentrations of plasma glucose in the early weeks postpartum. Despite greater milk yield by cows housed in freestalls, milk income minus feed costs including that of pasture was similar for the 3 management systems. Although these pasture systems might be a viable management system in the southeastern US, extensive loss of body weight immediately postpartum for pasture-based cows are a potential concern.

Animal Feed↗

PubMed2004

Chemical analysis and sensory evaluation of mahi-mahi (Cryphaena hippurus) during chilled storage.

Biogenic amines, total volatile base-nitrogen (TVB-N), and sensory evaluation are some of the indicators used for fish quality determination. Our objective was to evaluate the relationship among histamine, cadaverine, putrescine, TVB-N, and sensory evaluation as quality assessment tools. Two groups of six mahi-mahi fillets were refrigerated at 7 degrees C and sampled on days 0, 2, 4, 6, 8, and 10. On day 3, histamine, cadaverine, and putrescine levels reached 5, 3, and 0.5 mg/100 g, respectively, whereas TVB-N reached 30 mg/100 g. Sensory scores were 6 to 6.5 (10 very fresh and 1 very spoiled) for odor, appearance, texture, and color. Correlations were 0.78 and 0.72 between histamine and cadaverine and histamine and putrescine, 0.74 and 0.80 between TVB-N and cadaverine and TVB-N and putrescine, and 0.75 and 0.78 between odor and putrescine and odor and cadaverine. AromaMaps showed distinct trends for deteriorating mahi-mahi (Coryphaena hippurus) quality.

Animals↗

PubMed2003

A likelihood approach for mapping growth trajectories using dominant markers in a phase-unknown full-sib family.

Dominant markers have been commonly used in mapping quantitative trait loci (QTLs) in outcrossing species, in which not much prior genome information is available. But the dominant nature of these markers may lead to reduced QTL mapping precision and power. A new statistical method is proposed to incorporate growth laws into a QTL mapping framework, under which the use of the efficiency of dominant markers can be increased. This new method can be used to identify specific QTLs affecting differentiation in growth trajectories, and further estimate the timing of a QTL to turn on, or turn off, affecting growth during the entire ontogeny of a species. Using this method based on dominant markers we have successfully mapped a QTL for stem height growth trajectories to a linkage group in a forest tree. The implications of this method for the understanding of the genetic architecture of growth using dominant markers are discussed.

Chromosome Mapping↗

PubMed2001

A general polyploid model for analyzing gene segregation in outcrossing tetraploid species.

Polyploidy has played an important role in higher plant evolution and applied plant breeding. Polyploids are commonly categorized as allopolyploids resulting from the increase of chromosome number through hybridization and subsequent chromosome doubling or autopolyploids due to chromosome doubling of the same genome. Allopolyploids undergo bivalent pairing at meiosis because only homologous chromosomes pair. For autopolyploids, however, all homologous chromosomes can pair at the same time so that multivalents and, therefore, double reductions are formed. In this article, we use a maximum-likelihood method to develop a general polyploid model for estimating gene segregation patterns from molecular markers in a full-sib family derived from an arbitrary polyploid combining meiotic behaviors of both bivalent and multivalent pairings. Two meiotic parameters, one describing the preference of homologous chromosome pairing (expressed as the preferential pairing factor) typical of allopolyploids and the other specifying the degree of double reduction of autopolyploids, are estimated. The type of molecular markers used can be fully informative vs. partially informative or dominant vs. codominant. Simulation studies show that our polyploid model is well suited to estimate the preferential pairing factor and the frequency of double reduction at meiosis, which should help to characterize gene segregation in the progeny of autopolyploids. The implications of this model for linkage mapping, population genetic studies, and polyploid classification are discussed.

Crosses, Genetic↗

PubMed2001

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).

Animals↗

PubMed2000

Modelling covariance structure in the analysis of repeated measures data.

The term 'repeated measures' refers to data with multiple observations on the same sampling unit. In most cases, the multiple observations are taken over time, but they could be over space. It is usually plausible to assume that observations on the same unit are correlated. Hence, statistical analysis of repeated measures data must address the issue of covariation between measures on the same unit. Until recently, analysis techniques available in computer software only offered the user limited and inadequate choices. One choice was to ignore covariance structure and make invalid assumptions. Another was to avoid the covariance structure issue by analysing transformed data or making adjustments to otherwise inadequate analyses. Ignoring covariance structure may result in erroneous inference, and avoiding it may result in inefficient inference. Recently available mixed model methodology permits the covariance structure to be incorporated into the statistical model. The MIXED procedure of the SAS((R)) System provides a rich selection of covariance structures through the RANDOM and REPEATED statements. Modelling the covariance structure is a major hurdle in the use of PROC MIXED. However, once the covariance structure is modelled, inference about fixed effects proceeds essentially as when using PROC GLM. An example from the pharmaceutical industry is used to illustrate how to choose a covariance structure. The example also illustrates the effects of choice of covariance structure on tests and estimates of fixed effects. In many situations, estimates of linear combinations are invariant with respect to covariance structure, yet standard errors of the estimates may still depend on the covariance structure.

Analysis of Variance↗

PubMed2000

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.

Animal Feed↗

PubMed1999

HPLC method for analysis of free amino acids in fish using o-phthaldialdehyde precolumn derivatization.

Precolumn derivatization applying o-phthaldialdehyde (OPA) was used to analyze free lysine, histidine, and ornithine, precursors of the respective biogenic amines cadaverine, histamine, and putrescine, which are considered indicators of fish quality and safety. This method uses 75% methanol to eliminate the use of strong acids as the extraction solution. Each analysis took 35 min, was reproducible, and allowed separation of primary amino acids in fish samples. A binary solvent delivery system coupled with a fluorescence detector and an Ultrasphere ODS column were utilized for HPLC separation. Linearity of the calibration curves was very good (r(2) = 0.99) for the amino acids of interest. Minimum concentrations of detection were 40 pmol/mL for histidine and lysine and 70 pmol/mL for ornithine. Average recoveries were 72% for lysine, 93% for histidine, and 98% for ornithine. This method used solvent gradient elution to study the levels of these analytes in mahi-mahi, bigeye tuna, and flounder.

Amino Acids↗

PubMed1999

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.

Administration, Oral↗

PubMed1999

Genetic trends for milk yield of Jerseys and correlated changes in productive and reproductive performance.

Estimates of genetic trends in 24 measures of milk and constituent yields, somatic cell counts, and reproduction were obtained from 935 records of 374 Jerseys in a single herd. Data were obtained from a designed project for single-trait selection from 1969 through 1987. One line was subjected to selection solely for milk yield and included 259 cows; an unselected control line included 115 cows. Estimates of trends were based on differences in linear phenotypic trends between lines for first lactations, all lactations, and for 305-d and total records. The genetic changes in milk yield for these four data sets were 1.22 to 1.48%/yr (36.8 to 41.0 kg per cow yr) and 0.54 to 1.64%/yr for five constituent yields. Except for the percentages of minerals plus lactose, all constituent percentages decreased by 0.05 to 0.60%/yr. The ratios of protein to fat and solids-not-fat to fat increased 0.30 to 0.54%/yr, respectively. The number of services required per conception increased (0.17%) in first parity records and in all data (0.69%). The intervals from parturition to first estrus and from parturition to first service decreased in first lactation (1.19 and 0.82%) annually but increased (1.25 and 0.01%) in all data. Age of heifers at first estrus decreased by 0.44% annually. Most of the five measures of somatic cells decreased in first lactations but increased for all data. Estimates of realized genetic correlations of 14 measures of constituent yield and composition (four correlations each) agreed well with values expected from the literature. The results quantified change in milk yield, constituent yields and percentages, reproductive performance, and somatic cell counts in a single herd and should prove useful in the development of selection programs for dairy cattle.

Aging↗

PubMed1998

Performance and tissue zinc and metallothionein accumulation in chicks fed a high dietary level of zinc.

Four experiments were conducted to identify several factors that might improve the accuracy and reproducibility of Zn bioavailability assays for chicks. Response of tissue Zn and metallothionein (MT) concentrations to various elevated levels and soluble sources of dietary Zn were measured, as well as the effect of delaying high Zn administration until 7 d posthatching to alleviate the detrimental effect of Zn sulfate on feed intake to 3 wk of age. Bone Zn increased (P < 0.01) in all experiments in response to increasing dietary Zn concentrations. Liver and pancreas MT were affected (P < 0.01) by a source by age interaction and variability that made this criterion unsuitable for bioavailability assays. Lastly, 1-d-old chicks were used to study the effect of delaying feeding of a high-Zn diet up to 7 d of age. The basal diet was fed continuously for 21 d as a control. A diet containing 1,000 ppm Zn was either fed continuously from Day 1, or started on Day 3, 5, or 7. Chicks given high Zn on Day 3, 5, or 7 decreased (P < 0.01) feed intake within 24 h of feeding. Delayed feeding of high dietary Zn might help to alleviate decreased feed intake observed in previous studies. Delaying the onset of high Zn feeding by several days may help alleviate feed intake problems observed with Zn sulfate. Use of either Zn gluconate or Zn acetate as a standard in assays or use of MT synthesis as a bioavailability criterion will probably not be useful to improve accuracy of the estimates.

Aging↗

PubMed1998

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.

Analysis of Variance↗

PubMed1997

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.

Animals↗

PubMed1997

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.

Animals↗