P. R. Henry

Statistical evaluation of bioavailability assays

Publisher Summary Bioavailability of a nutrient in a test substance, relative to its bioavailability in a standard substance, is usually defined as the ratio of the amounts of the standard and test substances required to produce equivalent responses. Bioavailability assays are based on experimental data, and properly designed experiments should be conducted to obtain valid and efficient assays. The slope ratio assay is the most common form of assay used in recent bioavailability experiments. Values of independent and dependent variables are determined from each experimental unit. For relative bioavailability value (RBV) estimates must be meaningful, and the assumptions regarding linearity and intersection of the regression lines must hold. Statistical tests can be used to check the validity of the assumptions. The three-point design, as the name implies, relies on only three design points to estimate RBV. It can be used in the case of either the assumption for the slope ratio or the parallel lines assays, but it must be known in advance which assumption is valid. The standard curve assay is a compromise between the three-point assay and the slope ratio or parallel lines assays. It requires more than three data points, but usually not as many as the slope ratio or parallel lines assays. Some experiments have been conducted in which two or more sources of a nutrient were tested without a basal control group, which is needed to make a three-point comparison.

Relative bioavailability of copper in a copperlysine complex for chicks and lambs

Abstract Two experiments were conducted to study the relative bioavailability of Cu in a Cu-lysine complex with that of reagent grade CuSO 4 ·5H 2 O for chicks and lambs. Chicks were fed a basal diet (11 mg kg −1 Cu, dry matter (DM) basis) or the basal diet supplemented with 150, 300 or 450 mg kg −1 Cu from either of the two Cu sources for 18 days. Birds were killed and liver Cu concentrations determined. Liver biopsy samples were collected from wether lambs who were then fed the basal diet (9.5 mg kg −1 Cu DM) or the basal diet supplemented with 60, 120 or 180 mg kg −1 Cu from either source for 10 days. Copper in the initial biopsy was used as a covariate in the multiple linear regression of log 10 final liver Cu concentration on added dietary Cu concentration. Slope ratio comparisons gave relative Cu bioavailability values of 99 and 68 for Cu-lysine in chicks and lambs, respectively, compared with 100 for CuSO 4 ·5H 2 O for both species.

Estimation of the relative bioavailability of copper sources in chicks fed on conventional dietary amounts

Abstract 1. Tissue accumulation of Cu from dietary additions of 0, 5, 10, or 20 mg/kg Cu as reagent grade Cu acetate and feed grade Cu carbonate was determined in day‐old chicks fed on conventional maize‐soyabean meal starter diets (5.41 mg/kg Cu as‐fed basis) for 3 weeks. 2. Average daily food intake, daily weight gain and food conversion were similar among treatments. 3. There were linear increases in plasma and liver Cu concentrations (P< 0.01) as dietary Cu increased. 4. Bioavailability of Cu as carbonate was 0.66 that of Cu in the acetate based on the multiple regression slope ratio of liver Cu concentration on added dietary Cu. Although responses for the two Cu sources did not differ significantly, the relative bioavailability of the Cu carbonate was similar (0.66 vs 0.68) to that obtained in an earlier study (Ledoux et al., 1991) with greater dietary Cu contents (150, 300 and 450 mg/kg) in which the slopes of the equations representing the two sources differed (P<0.05).

Estimation of the relative bioavailability of zinc from inorganic zinc sources for sheep

Abstract Two experiments were conducted to study bioavailability of reagent (RG) and feed (FG) grade sources of Zn for sheep based on tissue Zn uptake and liver metallothionein (MT) concentration. In both experiments, 42 crossbred wether lambs were given a practical basal diet containing 44 mg kg −1 Zn (Exp. 1) or 64 mg kg −1 Zn (Exp. 2) for a 7 day adjustment period followed by experimental diets for 23 days. In Exp. 1, the basal diet was supplemented with 0, 700, 1400, or 2100 mg kg −1 Zn as RG ZnSO 4 · 7H 2 O (standard) or 1400 mg kg −1 Zn as RG Zn basic carbonate, Zn oxide, or metallic Zn. Based on multiple linear regression slope ratios of log 10 transformed accumulation of Zn in pancreas, liver and kidney on dietary Zn concentration, relative bioavailability estimates were sulfate 100, carbonate 106, oxide 106, and metal 76. In Exp. 2, added concentrations were the same and sources were FG sulfate-A (standard) or FG sulfate-B, oxide-A, and oxide-B. Bioavailability estimates on the same basis were 100, 86, 87, and 79 respectively. Use of liver MT as the response criterion gave estimates of 100, 88, 88, and 77 respectively.

Bioavailability of cobalt sources for ruminants. 2. Estimation of the relative value of reagent grade and feed grade cobalt sources from tissue cobalt accumulation and vitamin B12 concentrations

Abstract Three experiments were conducted to estimate the bioavailability of cobalt (Co) in reagent grade and feed grade Co sources for sheep. In Experiments 1 and 2, 27 mature sheep were assigned randomly to nine treatment groups. Treatments were the basal diet supplemented with 0, 20, 40, or 60 ppm reagent grade (RG) Co sulfate (standard) or 40 ppm Co as either RG Co oxide or Co carbonate or feed grade (FG) Co oxide, Co carbonate, or a Co oxide by-product (BP). Sheep were fed the experimental diets for 20 days. In Experiment 1, liver, kidney, heart, muscle, and spleen were collected. In Experiment 2, liver, kidney, and serum were collected. In Experiment 3, lambs were fed the basal control diet or basal supplemented with 0, 20, 40, or 60 ppm Co as RG Co sulfate or FG Co glucoheptonate for 16 days and liver, kidney, and serum were collected. Vitamin B 12 was determined in serum and liver in Experiment 3. Cobalt concentration was determined on all other samples. There was no effect of Co treatment on feed intake in any of the experiments. Tissue Co concentrations increased with Co supplementation in all three trials. In Experiment 1, serum and liver vitamin B 12 concentrations increased with increasing Co up to 40 ppm added Co. In Experiment 3, vitamin B 12 concentrations were variable but generally decreased with increasing Co as did total corrinoid concentrations. Based on liver and kidney Co concentrations the Co in Co sulfate, both carbonates and the glucoheptonate was more available than that in any of the three oxide forms.

Effect of high dietary zinc concentration and length of zinc feeding on feed intake and tissue zinc concentration in sheep

Abstract Two experiments were conducted to study the effect of high dietary Zn concentration and length of Zn feeding on feed intake and tissue Zn concentration in sheep. In Experiment 1, 24 whethers were fed a basal diet containing 41 mg kg −1 Zn dry matter (DM) basis and supplemented with 0, 500, 1000, 1500, 2000, or 2500 mg kg −1 Zn as reagent grade ZnSO 4 · 7H 2 O for 10 days and voluntary feed intake was measured daily. There was no difference in average feed intake among treatment groups. Intake of feed decreased between Day 2 and Day 5 for sheep given most diets, but recovered thereafter. In Experiment 2, 27 wethers were supplemented with 700, 1400, or 2100 mg kg −1 Zn added to the basal diet containing 30 mg kg −1 Zn (DM basis) for either 10, 20, or 30 days, in a 3 × 3 factorial arrangment of treatments. Three additional sheep were killed at the start of the experiment to serve as controls for tissue Zn concentration. Feed intake did not differ among treatments. There was no difference in bone, heart, or muscle Zn due to dietary treatment or time. Liver and kidney Zn increased with increasing dietary Zn and length of feeding period. Spleen Zn also increased with dietary Zn. The best fits to a linear model were found for liver and kidney Zn concentration at 20 days. These tissues appear to be the most sensitive for future Zn bioavailability studies with ruminants.

9 – Iron bioavailability

Publisher Summary The essentiality of iron has been known since ancient times and its beneficial effect on blood formation was recognized in the 17th century. There are two kinds of organic iron: hemal and nonhemal. Iron content of the body varies with species, age, sex, nutrition, and state of health and is controlled by adjustment in absorption rate. Attempts were made to determine bioavailability of iron sources by measuring hemoglobin regeneration dates back to the early 20th century. Amine and colleagues used a similar approach but compared slope ratios from the response of hemoglobin to graded concentrations of standard and test sources. It has already been reported that rats were more sensitive in detecting differences among iron sources than the chicks. In the first half of the 20th century, iron sources were often chosen for food enrichment based on their light color and chemical inertness rather than for the bioavailability of their iron. Extrinsic and intrinsic radiolabels with 59Fe have been used to study inorganic and nonheme iron bioavailability. Ferrous sulfate, ferric chloride, ferrous carbonate, and ferric oxide labeled with 59Fe were given to calves and lambs. Iron forms including iron dextran, iron dextrin, and gleptoferron have been effective sources of iron when administered as single intramuscular injections to baby pigs in the first 3 days of life. The importance of iron in human nutrition and the prevalence of iron deficiency among human populations have stimulated research on the bioavailability of iron in potential supplements of the element.

Bioavailability of cobalt sources for ruminants. 1. Effects of time and dietary cobalt concentration on tissue cobalt concentration

Abstract An experiment was conducted with 27 mature wethers initially averaging 59.8 ± 5.6 kg in body weight to study the effect of time and dietary Co concentration on tissue Co concentrations as a potential bioassay for Co sources. The 3 × 3 factorial arrangement of treatments included 0, 20, or 40 ppm added Co as reagent grade CoSO 4 ·H 2 O added to a basal diet containing 0.17 ppm Co and fed for 20, 40, or 60 d. Sheep were offered diets and tap water ad libitum. At the end of each period sheep were weighed and killed for tissue collection. At 20 d only livers were taken; thereafter kidney, spleen, skeletal muscle, and heart were also collected. There was no effect of time (P=0.07) or dietary Co (P=0.84) on average daily feed intake. Cobalt increased in liver (P

Relative bioavailability of copper in a copper-lysine complex or copper sulfate for ruminants as affected by feeding regimen

Abstract An experiment was conducted with 40 crossbred wether lambs to compare the relative bioavailability of Cu from a Cu-lysine complex with that from Cu sulfate under two feeding regimens. Liver biopsy samples were collected by a laparotomy technique and lambs were given 12 days to recover and adapt to individual pens. Lambs were fed either a control basal diet (9.8 mg kg −1 Cu dry matter (DM) basis) or basal supplemented with 180 mg kg −1 Cu as either reagent grade CuSO 4 · 5H 2 O or a feed-grade Cu-lysine complex. There were 12 lambs fed control diet and 14 lambs fed each Cu-supplemented diet. Half of the lambs given each diet were fed 1.0 kg of their respective diet once daily at 08:00 h. The remaining half were fed 1.0 kg in equal portions (166 g) six times during a 24 h period at 04:00 h, 08:00 h, 12:00 h, 16:00 h, 20:00 h and 24:00 h. Lambs were fed experimental diets for 10 days, then killed and livers removed for Cu analysis. Lambs fed once daily accumulated more ( P P > 0.10). Based on multiple linear regression slope ratio of log 10 transformed final liver Cu concentration on total intake of Cu (mg day −1 ) with the initial liver biopsy Cu concentration as a covariate, bioavailability of Cu from Cu-lysine relative to Cu sulfate was 93.4% ( P > 0.05) for combined feeding regimens.

6 – Cobalt bioavailability

Publisher Summary Gastrointestinal microflora of livestock synthesize vitamin B12 and its analogs from dietary cobalt, and, for ruminants and certain other animals, the quantities synthesized can be great enough to meet the host animals vitamin B12 requirement. Cobalt may be one of the mineral elements for which an in vitro assay may be more indicative of true availability than in vivo methods, because vitamin B12 production by the microflora is the actual physiological response to cobalt. Few studies exist in which comparisons in bioavailability among cobalt sources were made. Several authors have suggested that various cobalt compounds would be suitable as supplemental sources without providing research data. In general, studies with cobalt sources have consisted of supplementing deficient animals with a single source, possibly at a few added levels, and often under field conditions. The toxicity of a mineral element is related to its bioavailability. Ely and colleagues fed calves 500 mg of cobalt daily as cobalt chloride, sulfate, and carbonate for 30 days. Dietary factors that seem to have the greatest effect on ruminal production of vitamin B12 are cobalt concentration, roughage content of the diet, and total feed intake. The dietary addition of inorganic sulfate or cyanide in sheep decreased liver cobalt stores, but added dietary molybdenum increased liver cobalt. Very few critical tests of bioavailability of cobalt sources for ruminants have been made. The carbonate, chloride, sulfate, nitrate, and glucoheptonate forms of cobalt have been indicated to be effective supplemental sources of cobalt for ruminants, but not always with support of comparative data.