British Poultry Science
ISSN: 0007-1668 (Print) 1466-1799 (Online) Journal homepage: http://www.tandfonline.com/loi/cbps20
Effects of dietary calcium and available phosphorus concentration on digesta pH and on the availability of calcium, iron, magnesium and zinc from the intestinal contents of meat chickens T. M. Shafey , M. W. McDonald & J. G. Dingle To cite this article: T. M. Shafey , M. W. McDonald & J. G. Dingle (1991) Effects of dietary calcium and available phosphorus concentration on digesta pH and on the availability of calcium, iron, magnesium and zinc from the intestinal contents of meat chickens, British Poultry Science, 32:1, 185-194, DOI: 10.1080/00071669108417339 To link to this article: http://dx.doi.org/10.1080/00071669108417339
Published online: 08 Nov 2007.
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Citing articles: 21 View citing articles
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Date: 15 October 2015, At: 03:39
British Poultry Science (1991) 32: 185-194
EFFECTS OF DIETARY CALCIUM AND AVAILABLE PHOSPHORUS CONCENTRATION ON DIGESTA pH AND ON THE AVAILABILITY OF CALCIUM, IRON, MAGNESIUM AND ZINC FROM THE INTESTINAL CONTENTS OF MEAT CHICKENS T. M. SHAFEY, M. W. McDONALD AND J. G. DINGLE Gatton College, University of Queensland, Lawes, Qld, 4343, Australia
Downloaded by [Universite Laval] at 03:39 15 October 2015
Received for publication 13th March 1990
Abstract 1. The effects of high calcium intakes on the pH and availability of calcium, iron, magnesium and zinc in the gastrointestinal tract (GIT) contents of meat chickens were studied in two experiments. 2. A high dietary concentration of calcium (25.3 vs 10.7 g/kg) increased the pH of crop and ileum contents, but did not influence the pH of the contents of other segments of the GIT. 3. The solubilities of minerals in GIT contents were reduced and the size of dissolved mineral complexes were increased as the digesta moved from the duodenum and jejunum to the ileum. 4. After feeding diets with calcium and available phosphorus concentrations (15.3 and 4.3 g vs 21.8 and 4.3 g vs 22.6 and 8.3 g/kg), centrifugation of GIT contents showed that most (70-92%) of the calcium, iron, magnesium and zinc was in an insoluble form. High calcium diets reduced the proportion of soluble zinc associated with small complexes, and high calcium and available phosphorus diets reduced the proportions of soluble magnesium and zinc associated with small complexes. 5. These findings explain the mechanism of the reduced availability of zinc and magnesium in high calcium and high available phosphorus diets. INTRODUCTION
A major effect of high calcium concentrations in poultry diets may be a reduction in the bioavailability of other minerals. Diets high in calcium have been found to result in deficiencies of phosphorus (Scott et al., 1982; Shafey, 1988), zinc (Morrison and Sarrett, 1958; Roberson and Schaible, 1960), magnesium (Nugara and Edward, 1963) and iron (Sell, 1965). Apart from the pH of intestinal contents (Annekov, 1982), little information is available on the factors which cause variation in the concentration of soluble forms of minerals in various segments of the digestive tract. The potential bioavailability of 185
186
T. M. SHAFEY, M. W. MCDONALD AND J. G. DINGLE
calcium was studied by Wien and Schwartz (1985). Using a modified Wien and Schwartz technique, two experiments were undertaken to investigate the effects of concentrations of dietary calcium and phosphorus on the pH and availability of calcium, iron, magnesium and zinc in the gastrointestinal tract (GIT) of broiler chickens. MATERIALS AND METHODS
Downloaded by [Universite Laval] at 03:39 15 October 2015
Experiment 1
The effect of a diet high in calcium on the pH of GIT contents was investigated in this experiment. Forty, one-d-old chicks were assigned to two equal groups. One group was fed on the control diet (Table 1), while the second group was fed on the control diet plus 40 g of limestone per kg to produce 25-3 g calcium/kg. Chickens were individually caged with a separate feeding trough in an electrically heated battery brooder. They were fed for 12 d, fasted overnight and on the following day, fed for about 3 h before the experiment began. During the experimental period food and water were supplied ad libitum. At the end of the feeding trial, 7 birds from each treatment were anaesthetised by an intra-peritoneal injection of sodium pentobarbitone solution with a dose of 50 mg/kg body weight. Ether was used when further anaesthesia was required. Chickens were placed on their backs and their limbs tied down loosely to avoid placing excessive pressure on the GIT. The GIT was immediately exposed by making an incision in the left side of the body from the pectoral girdle to the vent. In order to minimise the possibility of mixing between contents of the segments, the GIT was clamped with artery forceps to separate the crop, proventriculus, gizzard, duodenum, jejunum and ileum. An incision of about 2 cm was made in the proximal portion of each segment. A combined needle glass silver/silver chloride electrode with 3 mm diameter barrel (Type No. U402-M3, Ingold. Co) attached to a pH meter was inserted into the incision and directed toward the vent. The pH was read when a steady value was obtained. The chickens were then killed. Experiment 2
The objectives of this experiment were to investigate the effects of site of the intestine and different dietary concentrations of calcium and available phosphorus on the solubility of calcium, iron, magnesium and zinc in the GIT contents. A total of 60 one-d-old unsexed broiler chickens were weighed and randomly assigned into 3 groups of 20 chickens each. Three experimental diets, whose dietary calcium and available phosphorus concentrations respectively were 15-3 and 4-3 g, 21*8 and 4-3 g and 22*6 and 8-3 g/kg, were used. Each diet was assigned to one of the 3 groups of chickens. The chickens were housed in an electrically heated battery brooder and other experimental conditions were as previously described for experiment 1. The compositions of the basal
THE AVAILABILITY OF MINERALS IN CHICKENS
187
and experimental diets respectively are shown in Tables 1 and 2. Increased concentrations of calcium and available phosphorus respectively were achieved in the diets by the addition of limestone and dicalcium phosphate. TABLE 1
The composition of the basal diets (g/kg)
Experiment
Downloaded by [Universite Laval] at 03:39 15 October 2015
1
2
Ingredient Wheat 767-2 442-3 290 Sorghum 40 50 Cottonseed meal 80 80 Soyabean meal 60 50 Meat meal (53% protein) 40 40 Fish meal (65% protein) 30 Skim milk powder 2-6 Limestone 11-5 3-8 Dicalcium phosphate 1-4 Sodium1 chloride 1-2 5 5 Premix Analysis 206 213 Crude protein (n X 6-25) Calcium 10-7 15-3 6-7 6-9 Total phosphorus 4-6 4-3 Calculated available phosphorus2 Calculated metabolisable energy (MJ/kg) 12-3 12-1 1 The composition of vitamins and minerals in the premix (per tonne of diet): Retinol, 12 g; cholecalciferol, 4 g; D-L tocopheryl acetate, lOg; riboflavin, 3 g; biotin, 0-5 g; pyridoxine HC1, 0-5 g; menadione sodium bisulphate, 1-0 g; zinc bacitracin (100 g/kg), 2-0 g; manganese sulphate, 60 g; zinc oxide, 50 g; ethoxyquin (330 g/kg), 150 g; DL-methionine, 500 g; L-lysine hydrochloride, 1000 g; furazolidone, 100 g; carrier (pollard), to 5 kg. 2 Calculation is based on 30% availability for phosphorus in plant products.
TABLE 2
The mineral composition of the diets (Experiment 2)
Treatment 1
2
3
Mineral supplement Limestone Dicalcium phosphate
18-6
6
22-5
Analysis of diet:
Calcium (gAg) 15-3 21-8 22-6 Calculated 1 4-3 4-3 8-3 available phosphorus (gAg) 1-9 2-3 Magnesium (gAg)2 2-2 162 227 408 Iron (mgAg)22 39 39 43 Zinc (mgAg) 1 Calculation is based on 30% availability for phosphorus in plant products. 2 Dietary mineral contents were calculated from Evans (1985).
Downloaded by [Universite Laval] at 03:39 15 October 2015
188
T. M. SHAFEY, M. W. MCDONALD AND J. G. DINGLE
At 12 d of age, 12 chickens per diet were selected, starved for 6 h then allowed to eat for 3 h. Each group of 12 was divided into three replicates of four chickens per diet; each bird was then killed by cardiac injection of pentobarbitone sodium diluted with an equal volume of water to prevent cardiac spasm observed when the anaesthetic is used undiluted. Badawy (1964) found that pentobarbitone sodium minimises the peristaltic movement of the contents of the GIT and the amount of mucosal shedding associated with other methods of killing. The small intestine was removed immediately after death and divided into duodenum+jejunum and ileum. The duodenum +jejunum was that portion from gizzard to the yolk stalk and the ileum was that portion from the yolk stalk to the ileocecal junction. The contents of each segment were pooled with replicates by squeezing into cleaned pre-weighed 50 ml centrifuge tubes. The samples were then weighed and mixed thoroughly for analysis. Fractionation of calcium, iron, magnesium and zinc was carried out using the combined techniques of centrifugation (to measure the potential bioavailability of these minerals) and ultrafiltration of the supernatant (to define the potential bioavailability of these minerals more precisely) (Wien and Schwartz, 1985). A known amount was taken for total calcium, iron, magnesium and zinc measurement, and the remainder of the intestinal contents were centrifuged at 10,000 g, at 4°C for 30 minutes. A known volume of supernatant was introduced into the ultrafiltration cell. An Amicon stirred cell 10 ml capacity was used at 4°C under continuous stirring with 95% nitrogen and 5% carbon dioxide mixture (30kPa), until 2 ml filtrate had been collected. Three membranes (with 100,000, 30,000 and 5000 molecular weight cut-offs (MWCO)) were used in the filtration process to measure the size of soluble mineral complexes in the digesta. Percent filterable mineral was calculated as— (//g mineral/ml of filtrate)/(//g mineral/ml intestinal supernatant) X 100. Samples from GIT contents were dried at 70°C before ashing at 600°C overnight. The ashed samples were digested according to AOAC methods (Hurwitz, 1980). Calcium, iron, magnesium and zinc were determined by atomic absorption spectrophotometry. Data was subjected to analysis of variance (Steel and Torrie, 1980). Where significant variance ratios were detected, differences between treatment means were tested using the least significant difference (LSD) procedure.
RESULTS
Experiment 1
The effects of increased calcium in the diet on the pH of the GIT contents are shown in Table 3. The higher dietary calcium concentration significantly increased the pH of the crop (P
ISSN: 0007-1668 (Print) 1466-1799 (Online) Journal homepage: http://www.tandfonline.com/loi/cbps20
Effects of dietary calcium and available phosphorus concentration on digesta pH and on the availability of calcium, iron, magnesium and zinc from the intestinal contents of meat chickens T. M. Shafey , M. W. McDonald & J. G. Dingle To cite this article: T. M. Shafey , M. W. McDonald & J. G. Dingle (1991) Effects of dietary calcium and available phosphorus concentration on digesta pH and on the availability of calcium, iron, magnesium and zinc from the intestinal contents of meat chickens, British Poultry Science, 32:1, 185-194, DOI: 10.1080/00071669108417339 To link to this article: http://dx.doi.org/10.1080/00071669108417339
Published online: 08 Nov 2007.
Submit your article to this journal
Article views: 39
View related articles
Citing articles: 21 View citing articles
Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=cbps20 Download by: [Universite Laval]
Date: 15 October 2015, At: 03:39
British Poultry Science (1991) 32: 185-194
EFFECTS OF DIETARY CALCIUM AND AVAILABLE PHOSPHORUS CONCENTRATION ON DIGESTA pH AND ON THE AVAILABILITY OF CALCIUM, IRON, MAGNESIUM AND ZINC FROM THE INTESTINAL CONTENTS OF MEAT CHICKENS T. M. SHAFEY, M. W. McDONALD AND J. G. DINGLE Gatton College, University of Queensland, Lawes, Qld, 4343, Australia
Downloaded by [Universite Laval] at 03:39 15 October 2015
Received for publication 13th March 1990
Abstract 1. The effects of high calcium intakes on the pH and availability of calcium, iron, magnesium and zinc in the gastrointestinal tract (GIT) contents of meat chickens were studied in two experiments. 2. A high dietary concentration of calcium (25.3 vs 10.7 g/kg) increased the pH of crop and ileum contents, but did not influence the pH of the contents of other segments of the GIT. 3. The solubilities of minerals in GIT contents were reduced and the size of dissolved mineral complexes were increased as the digesta moved from the duodenum and jejunum to the ileum. 4. After feeding diets with calcium and available phosphorus concentrations (15.3 and 4.3 g vs 21.8 and 4.3 g vs 22.6 and 8.3 g/kg), centrifugation of GIT contents showed that most (70-92%) of the calcium, iron, magnesium and zinc was in an insoluble form. High calcium diets reduced the proportion of soluble zinc associated with small complexes, and high calcium and available phosphorus diets reduced the proportions of soluble magnesium and zinc associated with small complexes. 5. These findings explain the mechanism of the reduced availability of zinc and magnesium in high calcium and high available phosphorus diets. INTRODUCTION
A major effect of high calcium concentrations in poultry diets may be a reduction in the bioavailability of other minerals. Diets high in calcium have been found to result in deficiencies of phosphorus (Scott et al., 1982; Shafey, 1988), zinc (Morrison and Sarrett, 1958; Roberson and Schaible, 1960), magnesium (Nugara and Edward, 1963) and iron (Sell, 1965). Apart from the pH of intestinal contents (Annekov, 1982), little information is available on the factors which cause variation in the concentration of soluble forms of minerals in various segments of the digestive tract. The potential bioavailability of 185
186
T. M. SHAFEY, M. W. MCDONALD AND J. G. DINGLE
calcium was studied by Wien and Schwartz (1985). Using a modified Wien and Schwartz technique, two experiments were undertaken to investigate the effects of concentrations of dietary calcium and phosphorus on the pH and availability of calcium, iron, magnesium and zinc in the gastrointestinal tract (GIT) of broiler chickens. MATERIALS AND METHODS
Downloaded by [Universite Laval] at 03:39 15 October 2015
Experiment 1
The effect of a diet high in calcium on the pH of GIT contents was investigated in this experiment. Forty, one-d-old chicks were assigned to two equal groups. One group was fed on the control diet (Table 1), while the second group was fed on the control diet plus 40 g of limestone per kg to produce 25-3 g calcium/kg. Chickens were individually caged with a separate feeding trough in an electrically heated battery brooder. They were fed for 12 d, fasted overnight and on the following day, fed for about 3 h before the experiment began. During the experimental period food and water were supplied ad libitum. At the end of the feeding trial, 7 birds from each treatment were anaesthetised by an intra-peritoneal injection of sodium pentobarbitone solution with a dose of 50 mg/kg body weight. Ether was used when further anaesthesia was required. Chickens were placed on their backs and their limbs tied down loosely to avoid placing excessive pressure on the GIT. The GIT was immediately exposed by making an incision in the left side of the body from the pectoral girdle to the vent. In order to minimise the possibility of mixing between contents of the segments, the GIT was clamped with artery forceps to separate the crop, proventriculus, gizzard, duodenum, jejunum and ileum. An incision of about 2 cm was made in the proximal portion of each segment. A combined needle glass silver/silver chloride electrode with 3 mm diameter barrel (Type No. U402-M3, Ingold. Co) attached to a pH meter was inserted into the incision and directed toward the vent. The pH was read when a steady value was obtained. The chickens were then killed. Experiment 2
The objectives of this experiment were to investigate the effects of site of the intestine and different dietary concentrations of calcium and available phosphorus on the solubility of calcium, iron, magnesium and zinc in the GIT contents. A total of 60 one-d-old unsexed broiler chickens were weighed and randomly assigned into 3 groups of 20 chickens each. Three experimental diets, whose dietary calcium and available phosphorus concentrations respectively were 15-3 and 4-3 g, 21*8 and 4-3 g and 22*6 and 8-3 g/kg, were used. Each diet was assigned to one of the 3 groups of chickens. The chickens were housed in an electrically heated battery brooder and other experimental conditions were as previously described for experiment 1. The compositions of the basal
THE AVAILABILITY OF MINERALS IN CHICKENS
187
and experimental diets respectively are shown in Tables 1 and 2. Increased concentrations of calcium and available phosphorus respectively were achieved in the diets by the addition of limestone and dicalcium phosphate. TABLE 1
The composition of the basal diets (g/kg)
Experiment
Downloaded by [Universite Laval] at 03:39 15 October 2015
1
2
Ingredient Wheat 767-2 442-3 290 Sorghum 40 50 Cottonseed meal 80 80 Soyabean meal 60 50 Meat meal (53% protein) 40 40 Fish meal (65% protein) 30 Skim milk powder 2-6 Limestone 11-5 3-8 Dicalcium phosphate 1-4 Sodium1 chloride 1-2 5 5 Premix Analysis 206 213 Crude protein (n X 6-25) Calcium 10-7 15-3 6-7 6-9 Total phosphorus 4-6 4-3 Calculated available phosphorus2 Calculated metabolisable energy (MJ/kg) 12-3 12-1 1 The composition of vitamins and minerals in the premix (per tonne of diet): Retinol, 12 g; cholecalciferol, 4 g; D-L tocopheryl acetate, lOg; riboflavin, 3 g; biotin, 0-5 g; pyridoxine HC1, 0-5 g; menadione sodium bisulphate, 1-0 g; zinc bacitracin (100 g/kg), 2-0 g; manganese sulphate, 60 g; zinc oxide, 50 g; ethoxyquin (330 g/kg), 150 g; DL-methionine, 500 g; L-lysine hydrochloride, 1000 g; furazolidone, 100 g; carrier (pollard), to 5 kg. 2 Calculation is based on 30% availability for phosphorus in plant products.
TABLE 2
The mineral composition of the diets (Experiment 2)
Treatment 1
2
3
Mineral supplement Limestone Dicalcium phosphate
18-6
6
22-5
Analysis of diet:
Calcium (gAg) 15-3 21-8 22-6 Calculated 1 4-3 4-3 8-3 available phosphorus (gAg) 1-9 2-3 Magnesium (gAg)2 2-2 162 227 408 Iron (mgAg)22 39 39 43 Zinc (mgAg) 1 Calculation is based on 30% availability for phosphorus in plant products. 2 Dietary mineral contents were calculated from Evans (1985).
Downloaded by [Universite Laval] at 03:39 15 October 2015
188
T. M. SHAFEY, M. W. MCDONALD AND J. G. DINGLE
At 12 d of age, 12 chickens per diet were selected, starved for 6 h then allowed to eat for 3 h. Each group of 12 was divided into three replicates of four chickens per diet; each bird was then killed by cardiac injection of pentobarbitone sodium diluted with an equal volume of water to prevent cardiac spasm observed when the anaesthetic is used undiluted. Badawy (1964) found that pentobarbitone sodium minimises the peristaltic movement of the contents of the GIT and the amount of mucosal shedding associated with other methods of killing. The small intestine was removed immediately after death and divided into duodenum+jejunum and ileum. The duodenum +jejunum was that portion from gizzard to the yolk stalk and the ileum was that portion from the yolk stalk to the ileocecal junction. The contents of each segment were pooled with replicates by squeezing into cleaned pre-weighed 50 ml centrifuge tubes. The samples were then weighed and mixed thoroughly for analysis. Fractionation of calcium, iron, magnesium and zinc was carried out using the combined techniques of centrifugation (to measure the potential bioavailability of these minerals) and ultrafiltration of the supernatant (to define the potential bioavailability of these minerals more precisely) (Wien and Schwartz, 1985). A known amount was taken for total calcium, iron, magnesium and zinc measurement, and the remainder of the intestinal contents were centrifuged at 10,000 g, at 4°C for 30 minutes. A known volume of supernatant was introduced into the ultrafiltration cell. An Amicon stirred cell 10 ml capacity was used at 4°C under continuous stirring with 95% nitrogen and 5% carbon dioxide mixture (30kPa), until 2 ml filtrate had been collected. Three membranes (with 100,000, 30,000 and 5000 molecular weight cut-offs (MWCO)) were used in the filtration process to measure the size of soluble mineral complexes in the digesta. Percent filterable mineral was calculated as— (//g mineral/ml of filtrate)/(//g mineral/ml intestinal supernatant) X 100. Samples from GIT contents were dried at 70°C before ashing at 600°C overnight. The ashed samples were digested according to AOAC methods (Hurwitz, 1980). Calcium, iron, magnesium and zinc were determined by atomic absorption spectrophotometry. Data was subjected to analysis of variance (Steel and Torrie, 1980). Where significant variance ratios were detected, differences between treatment means were tested using the least significant difference (LSD) procedure.
RESULTS
Experiment 1
The effects of increased calcium in the diet on the pH of the GIT contents are shown in Table 3. The higher dietary calcium concentration significantly increased the pH of the crop (P
