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Zinc antagonizing effects of fish meal, wheat bran and a corn-soybean meal mixture when added to a phytate-and fiber-free casein-dextrose diet
NUTRITION RESEARCH, Vol. 8, pp. 213-218, 1988 0271-5317/88 $3.00 + .00 Printed in the USA. Copyright (c) 1988 Pergamon Journals Ltd. All rights reserved.
ZINC ANTAGONIZING EFFECTS OF FISH MEAL, WHEATBRANAND A CORN-SOYBEAN MEAL MIXTURE WHENADDEDTO A PHYTATE- AND FIBER-FREE CASEIN-DEXTROSE DIET David H. Bakeri, Ph.D. and Kevin M. Halpin 2, Ph.D. Department of Animal Sciences University of I l l i n o i s , Urbana, I l l i n o i s 61801 ABSTRACT Two levels of dietary zinc (Zn), 68 and 318 mg/kg, were fed to young chicks in the presence or absence of 10% dietary additions of fish meal (FM), wheat bran (WB) or a corn-soybean meal mixture (C-SBM). As determined by Zn deposition in pancreas, bone and l i v e r , Zn u t i l i z a t i o n was severely depressed by addition of FM, WB or C-SBM to the phytate- and fiber-free casein-dextrose basal diet. The increase in pancreatic Zn concentration upon supplementing the basal diet (68 mg/kg Zn) with 250 mg/kg Zn from ZnCO3 was only 1.7% (C-SBM), 4.8% (FM) and 2.0% (WB) of that which resulted when the same quantity of Zn was added to the phytate- and fiber-free basal diet. Tibia and l i v e r uptakes of Zn were also markedly depressed by feed ingredient supplementation. Liver Zn concentration doubled when 250 mg/kg Zn was added to the basal diet, but C-SBM, FM or WB addition t o t a l l y prevented the increase in l i v e r Zn resulting from Zn supplementation. With 318 mg/kg dietary Zn, chicks fed the diet with no feed ingredient supplementation had three times more Zn in bone than in l i v e r and over twice as much Zn in pancreas as bone. In the presence of any one of the supplemental feed ingredients, however, Zn concentration in bone actually exceeded that present in pancreatic tissue. The data support the conclusion that phytate- and/or fiber-furnishing feed ingredients markedly reduce Zn u t i l i z a t i o n , but not all tissue storage sites of Zn are affected similarly. KEY WORDS: Zinc, Phytate, Fiber, Bone, Pancreas, Liver INTRODUCTION I t is well established that dietary Zn u t i l i z a t i o n is poor when conventional diets containing phytic acid and fiber are fed (1-6). I t is also known that the Zn-antagonizing effects of phytic acid are exacerbated by elevated dietary intakes of calcium (3-6). Our previous investigations into manganese homeostasis as affected by phytate and f i b e r sources revealed that corn, soybean meal, wheat bran and fish meal are markedly antagonistic to manganese u t i l i z a t i o n by chicks (7-9). Although fish meal is generally considered to be devoid of both fiber and phytate, quantitative analysis revealed that i t contained 8.1% neutral detergent fiber (NDF), most of which probably existed as chitin and c h i t i n - l i k e materials (9). ICorrespondence should be addressed to: D. H. Baker, 317 Mumford Hall, 1301 W. Gregory Drive, Urbana, I l l i n o i s 61801. 2Present address: I l l i n o i s 60018
National Dairy Council, 6300 North River Road, Rosemont, 213
214
D.H. BAKERAND K.M. HALPIN
Because Zn, like manganese, is an essential nutrient for poultry and other animals, including man, we deemed i t important to ascertain the extent to which some common phytate- and fiber-containing feed ingredients might influence uptake of dietary Zn by the common and often measured Zn storage sites: pancreas, bone and liver. Triplicate groups of three male crossbred chicks were assigned at 8 days posthatching to eight dietary treatments consisting of two levels of Zn, basal level (68 mg/kg) and basal + 250 mg/kg Zn from ZnCO3 (318 mg/kg), each provided in the presence and absence of 10% C-SBM, 10% FM or 10% WB. Feed ingredients were added to the basal diet (Table I) at the expense of dextrose. The basal casein-dextrose diet was designed, specifically, to be devoid of both phytic acid and fiber. Nutrient analyses of the feed ingredients are shown in Table 2. Chicks were housed in conventional chick starter batteries (three chicks/pen) in an environmentally controlled laboratory room (30 C) with constant light. Diets and water were provided ad libitum during the period 8 to 22 days posthatching. Details of allotment procedures have been described elsewhere (7).
TABLE 1 Composition of Phytate- and Fiber-Free Casein-Dextrose Basal Diet I
Ingredient
%
Dextrose Casein (92 % protein) Corn oil Mineral mixture 2 Vitamin mixture 3 Choline chloride DL-m-tocopheryl acetate, 20 mg/kg DL-methionine Glycine L-arginine NaHCO3
to 100.00 20.00 3.00 5.37 0.20 0.20 + 0.50 2.00 1.00 1.00
IContained 68 mg/kg Zn as determined by atomic absorption spectrophotometry. 2Mineral mixture provided per kilogram of diet: CaCO 3, 3.0 g; Ca3(P04)2, 28.0 g; K2HPO4,9.0 g; NaCl, 8.8 g; MgSO4.7H20,3.5 g; ferric citrate, 0.50 g; ZnCO3, 0.10 g; MnSO4.H20, 0.10 g; CuSO4.5H20, 20.0 mg; H3BO3, 9.0 mg; Na2MoO4-2H20, 9.0 mg; KI, 40.0 mg; CoSO4.7H20, 1.0 mg; Na2SeO3, 0.215 mg. 3Vitamin mixture provided per kilogram of diet: thiamin.HCl, 20 mg; niacin, 50 mg; riboflavin, 10 mg; D-Ca-pantothenate, 30 mg; vitamin B-12, 0.04 mg; pyridoxine.HCl, 6.0 mg; biotin, 0.6 mg; f o l i c acid, 4.0 mg; inositol, 100 mg; para-aminobenzoic acid, 2.0 mg; ascorbic acid, 250 mg; menadione, 2 mg; cholecalciferol (200,000 IU/g), 600 IU; retinyl acetate (650,000 IU/g), 5,200 IU.
ZINC UTILIZATION IN CHICKS
215
TABLE 2 Analytical Data on Menhaden Fish Meal (FM), Wheat Bran (WB) and the Corn-Soybean Meal Mixture (C-SBM)1
Item Crude protein 3, % NDF4, % Phytic acid5, % Ash6, % Calcium6, % Phosphorus6, % Zinc 6, mg/kg
C-SBM2
Feed ingredient FM
WB
23.20 10.30 1.66 3.10 0.15 0.80 35.20
59.70 8.10 -14.50 3.71 3.20 93.70
12.60 40.30 1.92 5.40 0.11 1.15 71.70
1Average of duplicate determinations; data expressed on an air-dry (as fed) basis. 257.33% corn and 42.67% soybean meal. 3Kjeldahl N x 6.25. 4Neutral detergent fiber (10). 5Determined according to procedures described by Thompson and Erdman (11). 6Standard AOACanalytical methodology (12).
At the end of the 14-day feeding period, all chicks were killed by cervical dislocation and their liver, pancreas and right tibia removed for subsequent analysis of Zn. Liver and pancreatic tissue samples were pooled by replicate (three/replicate; three replicates), dried at 100 C for 24 hours, weighed and then wet ashed with HNO3 and H202 (30%). Tibia samples were similarly pooled by replicate group and then ashed at 600 C for 24 hours. All three tissues were analyzed for Zn by atomic absorption spectrophotometry (Perkin-E]mer, Model 306). All data were analyzed statistically by appropriate analysis of variance procedures (13). Single degree-of-freedom comparisons were made to assess treatment differences. RESULTS Because all diets fed were adequate in all known essential nutrients, including Zn, chick growth was similar among treatments, with the exception that feed ingredient supplementation tended to increase consumption, a result observed previously in our laboratory (7-9). Thus, 14-day gains (g) were, basal level of Zn: 239 (basal), 262 (C-SBM), 263 (FM) and 257 (WB) at feed intakes (g) of 358 (basal), 374 (C-SBM), 364 (FM) and 379 (WB). Chicks fed diets containing 250 mg/kg added Zn gained 252 (basal), 264 (C-SBM), 273 (FM) and 253 (WB) g at 14-day feed intakes (g) of 362 (basal), 363 (C-SBM), 375 (FM) and 379 (WB). With no inorganic Zn added to the casein-dextrose basal diet (68 mg/kg Zn) all feed ingredients slightly depressed pancreatic and bone, but not liver, Zn concentration. With 250 mg/kg added Zn, however, all tissues examined accumulated much less Zn in the presence than in the absence of supplemental C-SBM, FM or WB.
216
D.H. BAKERAND K.M. HALPIN
Adding 250 mg/kg Zn to the basal diet caused Zn accumulation in all t i s sues examined, particularly pancreatic tissue where Zn concentration increased sixfold. With C-SBM, FM or WB in the diet, however, Zn supplementation caused only modest increases in pancreatic and bone Zn concentrations. Liver Zn did not increase in response to adding inorganic Zn to diets containing C-SBM, FM or WB.
TABLE 3 Tissue Zinc Concentrations in Chicks Fed a Phytate- and Fiber-Free Diet Supplemented With Fish Meal (FM), Wheat Bran (WB) or a Corn-Soybean Meal Mixture (C-SBM)1 Dietary Zn addition from ZnCO3 02 Ingredient supplemented
None
C-SBM (10%)5 FM (10%) WB (10%)
250 mg/kg
Zn intake
Pancreas Bone Liver Zn Zn Zn
Zn intake
Pancreas Bone Liver Zn Zn Zn
mg
~g/g dry tissue 3,4
mg
Ng/g dry tissue 3,4
24.34 26.74 28.17 28.50
149 129 127 120
219 210 202 193
78.1 85.4 82.8 89.7
115.1 116.7 122.8 123.2
929 142 166 136
431 236 252 217
143.9 80.4 87.2 81.7
IData are means of t r i p l i c a t e groups of three chicks/group that received the experimental diets during the 14-day period 8 to 22 days posthatching. 2The basal diet with no supplemental feed ingredients contained 68 mg/kg Zn of which 52 mg/kg came from ZnCO3 and 16 mg/kg came from casein. 3Heterogeneous variance precluded SEM determinations for pancreatic Zn. These data were therefore log transformed prior to s t a t i s t i c a l analysis. Pooled SEM for bone Zn and l i v e r Zn were 21.9 and 6.0 ~g/g, respectively. 4Statistical interactions of Zn level x C-SBM, Zn level x FM and Zn level x WB were significant (P
DISCUSSION Using data in Table 3, i t was possible to calculate the change in Zn concentration in tissues (0 vs. 250 mg/kg added Zn, cf. Table 3) per unit change in Zn intake (0 vs. 250 mg/kg added Zn). These calculated bioavaila b i l i t y (BV) values 3 provide interesting insight concerning the extent to which C-SBM, FM and WB decreased Zn u t i l i z a t i o n . The BV values expressed as a percent of basal values ( i . e . , no feed ingredient supplementation) resulted 3For pancreatic Zn, and using basal and C-SBM addition, for example, BV is calculated as follows: BV (basal) =
929-149 = 8.59; 115.1-24.34
BV (C-SBM) -
142-129 = 0.144 116.7-26.74
ZINC UTILIZATION IN CHICKS
217
in relative Zn BV estimates of 1.7%4 (C-SBM), 4.8% (FM) and 2.0% (WB) using pancreas, and 12.4% (C-SBM), 22.6% (FM) and 10.8% (WB) using t i b i a data. Since l i v e r Zn did not respond to 250 mg/kg Zn supplementation, BV calculations using this tissue were deemed inappropriate. Nonetheless, i t is of considerable interest that presence of 10% C-SBM or 10% WB in the diet t o t a l l y prevented an increase in Zn deposition in livers of chicks fed 250 mg/kg added inorganic Zn compared with those fed no supplemental Zn. Based upon data in Table 3, Zn u t i l i z a t i o n was markedly impaired by adding C-SBM, FM or WB to the phytate- and fiber-free basal diet in the range of dietary Zn levels of 68 to 318 mg/kg. Because Zn accumulation in tissues is not a linear function of Zn intake 5, one cannot assume that C-SBM, FM or WB would have similar quantitative effects on Zn uptake by tissues of chicks fed diets containing between 0 and 68 mg/kg Zn. Also, i t is not known whether addition of either FM or WB to a conventional C-SBM diet would depress Zn u t i l i z a t i o n more than that already occurring as a result of the ingestion of corn and soybean meal. The ingredients selected for use in this study provided a cross section of factors thought to be involved in antagonism of trace-mineral u t i l i z a t i o n . Thus, C-SBM contained a modest amount of NDF and very l i t t l e calcium, but i t provided considerable phytic acid. Likewise, WB provided considerable phytate, and very l i t t l e calcium; NDF (mostly cellulose and hemicellulose), however, was plentiful in WB. Fish meal, on the other hand, was devoid of phytate, but rich in calcium. I t was also devoid of cellulose and hemicellulose, but nonetheless was analyzed to contain 8.10% NDF, probably a reflection o f i t s chitin and c h i t i n - l i k e material content. That all feed ingredients depressed Zn accumulation in tissues suggests that factors other than phytate and (conventional) fiber may be involved in the Zn-antagonizing effects of common feed ingredients. Indeed, addition of these ingredients to our purified diet, despite providing from 3.5 (C-SBM) to 9.4 (FM) mg/kg Zn, actually depressed tissue concentrations of Zn. This suggests that the ingredients in question not only provided no bioavailable Zn, but they also reduced u t i l i zation of the inorganic (and casein-derived) Zn present in the basal diet. I t seems obvious, therefore, that the minimal dietary need for Zn must be considerably higher when a conventional diet is fed than when a purified diet is fed. Also, because FM was found to antagonize Zn u t i l i z a t i o n , i t must be concluded that plant-source phytate and f i b e r are not the only contributors to poor Zn u t i l i z a t i o n when conventional food and feed ingredients are consumed. In an experiment such as that reported here, addition of feed ingredients to a purified diet provides a plethora of chemical e n t i t i e s other than fiber, phytate and calcium. I t is not known what effect, i f any, these other components may have had on Zn u t i l i z a t i o n . Previous work from our laboratory, however, indicated that both the ash and NDF components of FM and WB, but only the NDF portion of C-SBM, would impart antagonizing effects on Mn u t i l i z a t i o n (9). 40.144 8.59 x 100 = 1.7% 5Unpublished data from our laboratory have led to the conclusion that Zn concentration in tissues and plasma is not a straight-line function of Zn intake, whether working below or above the chick's minimal Zn requirement of 15 mg/kg when a phytate- and fiber-free diet is fed (14).
218
D.H. BAKERAND K.M. HALPIN
REFERENCES 1.
O'Dell BL, Miller ER, Miller WJ. Copper and Zinc in Poultry, Swine and Ruminant Nutrition. Natl. Feed Ingred. Assn., West Des Moines, Iowa. 1979; pp. 24-57.
2.
O'Dell BL, Savage JE. Effect of phytic acid on zinc availability. Proc. Soc. Exp. Biol. Med. 1960; 103:304-6.
3.
O'Del] BL, Yohe JM, Savage JE. Zinc a v a i l a b i l i t y in the chick as affected by phytate, calcium and ethylene diamine-tetra-acetate. Poul. Sci. 1964; 43:415-9.
4.
Bafundo KW, Baker DH, Fitzgerald PR. Zinc utilization in the chick as influenced by dietary concentrations of calcium and phytate and by Eimeria aoervulina infection. Poul. Sci. 1984; 63:2430-7.
5.
Erdman JW. Oilseed phytates: Chem. Soc. 1979; 56:736-41.
6.
Fordyce EJ, Forbes RM, Robbins KR, Erdman JW. Phytate x calcium molar ratios: are they predictive of zinc bioavailabi]ity? J. Food Sci. 1987; 52:440-4.
7.
Halpin I~M, Baker DH. Manganese u t i l i z a t i o n in the chick: effects of corn, soybean meal, fish meal, wheat bran and rice bran on tissue uptake of manganese. Poul. Sci. 1986; 65:995-1003.
8.
Ha]pin KM, Baker DH. Long-term effects of corn, soybean meal, wheat bran and fish meal on manganese u t i l i z a t i o n in the chick. Poul Sci. 1986; 65:1371-4.
9.
Ha]pin KM, Baker DH. Mechanism of the tissue manganese-lowering effect of corn, soybean meal, fish meal, wheat bran and rice bran. Poul. Sci. 1987; 66:332-40.
nutritional implications.
J. Am. Oil
10.
Van Soest PJ, Wine RH. Use of detergents in the analysis of fibrous feeds. IV. Determination of plant cell-wall constituents. J. Assn. Official Anal. Chem. 1967; 50:50-5.
11.
Thompson DB, Erdman JW. Phytic acid determination in soybeans. Food S c i . 1982; 47:513-7.
12.
A.O.A.C. Official Methods of Analysis, 8th ed., Association of Official Agricultural Chemists, Washington, D.C. 1975.
13.
Steel RGD, Torrie JH. Principles and Procedures of Statistics: A Biometrical Approach. 2nd ed. McGraw-Hill Book Co., Inc. New York, NY.
14.
Southern LL, Baker DH. Zinc t o x i c i t y , zinc deficiency and zinc-copper interrelationship in Eimeria acervuZina-infected chicks. J. Nutr. 1983; 113:688-96.
Accepted for publication September 9, 1987
J.
ZINC ANTAGONIZING EFFECTS OF FISH MEAL, WHEATBRANAND A CORN-SOYBEAN MEAL MIXTURE WHENADDEDTO A PHYTATE- AND FIBER-FREE CASEIN-DEXTROSE DIET David H. Bakeri, Ph.D. and Kevin M. Halpin 2, Ph.D. Department of Animal Sciences University of I l l i n o i s , Urbana, I l l i n o i s 61801 ABSTRACT Two levels of dietary zinc (Zn), 68 and 318 mg/kg, were fed to young chicks in the presence or absence of 10% dietary additions of fish meal (FM), wheat bran (WB) or a corn-soybean meal mixture (C-SBM). As determined by Zn deposition in pancreas, bone and l i v e r , Zn u t i l i z a t i o n was severely depressed by addition of FM, WB or C-SBM to the phytate- and fiber-free casein-dextrose basal diet. The increase in pancreatic Zn concentration upon supplementing the basal diet (68 mg/kg Zn) with 250 mg/kg Zn from ZnCO3 was only 1.7% (C-SBM), 4.8% (FM) and 2.0% (WB) of that which resulted when the same quantity of Zn was added to the phytate- and fiber-free basal diet. Tibia and l i v e r uptakes of Zn were also markedly depressed by feed ingredient supplementation. Liver Zn concentration doubled when 250 mg/kg Zn was added to the basal diet, but C-SBM, FM or WB addition t o t a l l y prevented the increase in l i v e r Zn resulting from Zn supplementation. With 318 mg/kg dietary Zn, chicks fed the diet with no feed ingredient supplementation had three times more Zn in bone than in l i v e r and over twice as much Zn in pancreas as bone. In the presence of any one of the supplemental feed ingredients, however, Zn concentration in bone actually exceeded that present in pancreatic tissue. The data support the conclusion that phytate- and/or fiber-furnishing feed ingredients markedly reduce Zn u t i l i z a t i o n , but not all tissue storage sites of Zn are affected similarly. KEY WORDS: Zinc, Phytate, Fiber, Bone, Pancreas, Liver INTRODUCTION I t is well established that dietary Zn u t i l i z a t i o n is poor when conventional diets containing phytic acid and fiber are fed (1-6). I t is also known that the Zn-antagonizing effects of phytic acid are exacerbated by elevated dietary intakes of calcium (3-6). Our previous investigations into manganese homeostasis as affected by phytate and f i b e r sources revealed that corn, soybean meal, wheat bran and fish meal are markedly antagonistic to manganese u t i l i z a t i o n by chicks (7-9). Although fish meal is generally considered to be devoid of both fiber and phytate, quantitative analysis revealed that i t contained 8.1% neutral detergent fiber (NDF), most of which probably existed as chitin and c h i t i n - l i k e materials (9). ICorrespondence should be addressed to: D. H. Baker, 317 Mumford Hall, 1301 W. Gregory Drive, Urbana, I l l i n o i s 61801. 2Present address: I l l i n o i s 60018
National Dairy Council, 6300 North River Road, Rosemont, 213
214
D.H. BAKERAND K.M. HALPIN
Because Zn, like manganese, is an essential nutrient for poultry and other animals, including man, we deemed i t important to ascertain the extent to which some common phytate- and fiber-containing feed ingredients might influence uptake of dietary Zn by the common and often measured Zn storage sites: pancreas, bone and liver. Triplicate groups of three male crossbred chicks were assigned at 8 days posthatching to eight dietary treatments consisting of two levels of Zn, basal level (68 mg/kg) and basal + 250 mg/kg Zn from ZnCO3 (318 mg/kg), each provided in the presence and absence of 10% C-SBM, 10% FM or 10% WB. Feed ingredients were added to the basal diet (Table I) at the expense of dextrose. The basal casein-dextrose diet was designed, specifically, to be devoid of both phytic acid and fiber. Nutrient analyses of the feed ingredients are shown in Table 2. Chicks were housed in conventional chick starter batteries (three chicks/pen) in an environmentally controlled laboratory room (30 C) with constant light. Diets and water were provided ad libitum during the period 8 to 22 days posthatching. Details of allotment procedures have been described elsewhere (7).
TABLE 1 Composition of Phytate- and Fiber-Free Casein-Dextrose Basal Diet I
Ingredient
%
Dextrose Casein (92 % protein) Corn oil Mineral mixture 2 Vitamin mixture 3 Choline chloride DL-m-tocopheryl acetate, 20 mg/kg DL-methionine Glycine L-arginine NaHCO3
to 100.00 20.00 3.00 5.37 0.20 0.20 + 0.50 2.00 1.00 1.00
IContained 68 mg/kg Zn as determined by atomic absorption spectrophotometry. 2Mineral mixture provided per kilogram of diet: CaCO 3, 3.0 g; Ca3(P04)2, 28.0 g; K2HPO4,9.0 g; NaCl, 8.8 g; MgSO4.7H20,3.5 g; ferric citrate, 0.50 g; ZnCO3, 0.10 g; MnSO4.H20, 0.10 g; CuSO4.5H20, 20.0 mg; H3BO3, 9.0 mg; Na2MoO4-2H20, 9.0 mg; KI, 40.0 mg; CoSO4.7H20, 1.0 mg; Na2SeO3, 0.215 mg. 3Vitamin mixture provided per kilogram of diet: thiamin.HCl, 20 mg; niacin, 50 mg; riboflavin, 10 mg; D-Ca-pantothenate, 30 mg; vitamin B-12, 0.04 mg; pyridoxine.HCl, 6.0 mg; biotin, 0.6 mg; f o l i c acid, 4.0 mg; inositol, 100 mg; para-aminobenzoic acid, 2.0 mg; ascorbic acid, 250 mg; menadione, 2 mg; cholecalciferol (200,000 IU/g), 600 IU; retinyl acetate (650,000 IU/g), 5,200 IU.
ZINC UTILIZATION IN CHICKS
215
TABLE 2 Analytical Data on Menhaden Fish Meal (FM), Wheat Bran (WB) and the Corn-Soybean Meal Mixture (C-SBM)1
Item Crude protein 3, % NDF4, % Phytic acid5, % Ash6, % Calcium6, % Phosphorus6, % Zinc 6, mg/kg
C-SBM2
Feed ingredient FM
WB
23.20 10.30 1.66 3.10 0.15 0.80 35.20
59.70 8.10 -14.50 3.71 3.20 93.70
12.60 40.30 1.92 5.40 0.11 1.15 71.70
1Average of duplicate determinations; data expressed on an air-dry (as fed) basis. 257.33% corn and 42.67% soybean meal. 3Kjeldahl N x 6.25. 4Neutral detergent fiber (10). 5Determined according to procedures described by Thompson and Erdman (11). 6Standard AOACanalytical methodology (12).
At the end of the 14-day feeding period, all chicks were killed by cervical dislocation and their liver, pancreas and right tibia removed for subsequent analysis of Zn. Liver and pancreatic tissue samples were pooled by replicate (three/replicate; three replicates), dried at 100 C for 24 hours, weighed and then wet ashed with HNO3 and H202 (30%). Tibia samples were similarly pooled by replicate group and then ashed at 600 C for 24 hours. All three tissues were analyzed for Zn by atomic absorption spectrophotometry (Perkin-E]mer, Model 306). All data were analyzed statistically by appropriate analysis of variance procedures (13). Single degree-of-freedom comparisons were made to assess treatment differences. RESULTS Because all diets fed were adequate in all known essential nutrients, including Zn, chick growth was similar among treatments, with the exception that feed ingredient supplementation tended to increase consumption, a result observed previously in our laboratory (7-9). Thus, 14-day gains (g) were, basal level of Zn: 239 (basal), 262 (C-SBM), 263 (FM) and 257 (WB) at feed intakes (g) of 358 (basal), 374 (C-SBM), 364 (FM) and 379 (WB). Chicks fed diets containing 250 mg/kg added Zn gained 252 (basal), 264 (C-SBM), 273 (FM) and 253 (WB) g at 14-day feed intakes (g) of 362 (basal), 363 (C-SBM), 375 (FM) and 379 (WB). With no inorganic Zn added to the casein-dextrose basal diet (68 mg/kg Zn) all feed ingredients slightly depressed pancreatic and bone, but not liver, Zn concentration. With 250 mg/kg added Zn, however, all tissues examined accumulated much less Zn in the presence than in the absence of supplemental C-SBM, FM or WB.
216
D.H. BAKERAND K.M. HALPIN
Adding 250 mg/kg Zn to the basal diet caused Zn accumulation in all t i s sues examined, particularly pancreatic tissue where Zn concentration increased sixfold. With C-SBM, FM or WB in the diet, however, Zn supplementation caused only modest increases in pancreatic and bone Zn concentrations. Liver Zn did not increase in response to adding inorganic Zn to diets containing C-SBM, FM or WB.
TABLE 3 Tissue Zinc Concentrations in Chicks Fed a Phytate- and Fiber-Free Diet Supplemented With Fish Meal (FM), Wheat Bran (WB) or a Corn-Soybean Meal Mixture (C-SBM)1 Dietary Zn addition from ZnCO3 02 Ingredient supplemented
None
C-SBM (10%)5 FM (10%) WB (10%)
250 mg/kg
Zn intake
Pancreas Bone Liver Zn Zn Zn
Zn intake
Pancreas Bone Liver Zn Zn Zn
mg
~g/g dry tissue 3,4
mg
Ng/g dry tissue 3,4
24.34 26.74 28.17 28.50
149 129 127 120
219 210 202 193
78.1 85.4 82.8 89.7
115.1 116.7 122.8 123.2
929 142 166 136
431 236 252 217
143.9 80.4 87.2 81.7
IData are means of t r i p l i c a t e groups of three chicks/group that received the experimental diets during the 14-day period 8 to 22 days posthatching. 2The basal diet with no supplemental feed ingredients contained 68 mg/kg Zn of which 52 mg/kg came from ZnCO3 and 16 mg/kg came from casein. 3Heterogeneous variance precluded SEM determinations for pancreatic Zn. These data were therefore log transformed prior to s t a t i s t i c a l analysis. Pooled SEM for bone Zn and l i v e r Zn were 21.9 and 6.0 ~g/g, respectively. 4Statistical interactions of Zn level x C-SBM, Zn level x FM and Zn level x WB were significant (P
DISCUSSION Using data in Table 3, i t was possible to calculate the change in Zn concentration in tissues (0 vs. 250 mg/kg added Zn, cf. Table 3) per unit change in Zn intake (0 vs. 250 mg/kg added Zn). These calculated bioavaila b i l i t y (BV) values 3 provide interesting insight concerning the extent to which C-SBM, FM and WB decreased Zn u t i l i z a t i o n . The BV values expressed as a percent of basal values ( i . e . , no feed ingredient supplementation) resulted 3For pancreatic Zn, and using basal and C-SBM addition, for example, BV is calculated as follows: BV (basal) =
929-149 = 8.59; 115.1-24.34
BV (C-SBM) -
142-129 = 0.144 116.7-26.74
ZINC UTILIZATION IN CHICKS
217
in relative Zn BV estimates of 1.7%4 (C-SBM), 4.8% (FM) and 2.0% (WB) using pancreas, and 12.4% (C-SBM), 22.6% (FM) and 10.8% (WB) using t i b i a data. Since l i v e r Zn did not respond to 250 mg/kg Zn supplementation, BV calculations using this tissue were deemed inappropriate. Nonetheless, i t is of considerable interest that presence of 10% C-SBM or 10% WB in the diet t o t a l l y prevented an increase in Zn deposition in livers of chicks fed 250 mg/kg added inorganic Zn compared with those fed no supplemental Zn. Based upon data in Table 3, Zn u t i l i z a t i o n was markedly impaired by adding C-SBM, FM or WB to the phytate- and fiber-free basal diet in the range of dietary Zn levels of 68 to 318 mg/kg. Because Zn accumulation in tissues is not a linear function of Zn intake 5, one cannot assume that C-SBM, FM or WB would have similar quantitative effects on Zn uptake by tissues of chicks fed diets containing between 0 and 68 mg/kg Zn. Also, i t is not known whether addition of either FM or WB to a conventional C-SBM diet would depress Zn u t i l i z a t i o n more than that already occurring as a result of the ingestion of corn and soybean meal. The ingredients selected for use in this study provided a cross section of factors thought to be involved in antagonism of trace-mineral u t i l i z a t i o n . Thus, C-SBM contained a modest amount of NDF and very l i t t l e calcium, but i t provided considerable phytic acid. Likewise, WB provided considerable phytate, and very l i t t l e calcium; NDF (mostly cellulose and hemicellulose), however, was plentiful in WB. Fish meal, on the other hand, was devoid of phytate, but rich in calcium. I t was also devoid of cellulose and hemicellulose, but nonetheless was analyzed to contain 8.10% NDF, probably a reflection o f i t s chitin and c h i t i n - l i k e material content. That all feed ingredients depressed Zn accumulation in tissues suggests that factors other than phytate and (conventional) fiber may be involved in the Zn-antagonizing effects of common feed ingredients. Indeed, addition of these ingredients to our purified diet, despite providing from 3.5 (C-SBM) to 9.4 (FM) mg/kg Zn, actually depressed tissue concentrations of Zn. This suggests that the ingredients in question not only provided no bioavailable Zn, but they also reduced u t i l i zation of the inorganic (and casein-derived) Zn present in the basal diet. I t seems obvious, therefore, that the minimal dietary need for Zn must be considerably higher when a conventional diet is fed than when a purified diet is fed. Also, because FM was found to antagonize Zn u t i l i z a t i o n , i t must be concluded that plant-source phytate and f i b e r are not the only contributors to poor Zn u t i l i z a t i o n when conventional food and feed ingredients are consumed. In an experiment such as that reported here, addition of feed ingredients to a purified diet provides a plethora of chemical e n t i t i e s other than fiber, phytate and calcium. I t is not known what effect, i f any, these other components may have had on Zn u t i l i z a t i o n . Previous work from our laboratory, however, indicated that both the ash and NDF components of FM and WB, but only the NDF portion of C-SBM, would impart antagonizing effects on Mn u t i l i z a t i o n (9). 40.144 8.59 x 100 = 1.7% 5Unpublished data from our laboratory have led to the conclusion that Zn concentration in tissues and plasma is not a straight-line function of Zn intake, whether working below or above the chick's minimal Zn requirement of 15 mg/kg when a phytate- and fiber-free diet is fed (14).
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D.H. BAKERAND K.M. HALPIN
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Accepted for publication September 9, 1987
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