Abstract
A chick assay was conducted to determine the effects of Zn source on performance and to establish a Zn relative bioavailability value (RBV) for a new source of Zn hydroxychloride. In the assay, 8-day-old chicks were fed a Zn-deficient soy protein concentrate diet supplemented with 0, 7, and 15 mg Zn/kg from feed grade ZnSO4 monohydrate for 14 d to establish a standard response curve. The same basal diet was supplemented with 3, 7, and 10 mg Zn/kg from a new Zn hydroxychloride (SAMZn). A second source of Zn hydroxychloride (IBZn) was supplemented at 10 mg Zn/kg as a direct comparison to the highest level of SAMZn. Weight gain increased (P < 0.05) with increasing Zn level, regardless of source. Weight gain of chicks fed 7 mg Zn/kg from SAMZn was not different (P > 0.05) from chicks fed 15 mg Zn/kg from ZnSO4. Weight gain was not different (P > 0.05) when comparing the 2 sources of Zn hydroxychloride supplemented at 10 mg Zn/kg. Tibia ash Zn and total tibia Zn were increased (P < 0.05) by all Zn sources and responded linearly (P < 0.05) to Zn supplementation from ZnSO4 and SAMZn. Total tibia Zn concentration was not different (P > 0.05) for chicks fed 10 mg Zn/kg from either source of Zn hydroxychloride. Multiple linear regression of total tibia Zn on supplemental Zn intake (R2 = 0.95) resulted in a RBV of 115% for SAMZn compared with ZnSO4 (set at 100%). The RBV of SAMZn was higher (P < 0.05) than ZnSO4. In conclusion, relative bioavailability of Zn (based on tibia Zn) in Zn hydroxychloride from SAMZn was higher than feed grade ZnSO4 based on multiple regression slope-ratio analysis and was similar to that of IBZn Zn hydroxychloride based on tibia Zn responses to 10 mg/kg supplemental dietary Zn.
Key words: zinc sulfate, zinc hydroxychloride, growth, bioavailability, chick
INTRODUCTION
Zinc is a trace mineral essential for many biological processes in the body, such as growth, bone development, feathering, and optimal immune system function. Zinc is commonly supplemented in commercial poultry diets. Historically, the source of supplemental Zn is an inorganic salt, such as zinc oxide (ZnO) or zinc sulfate (ZnSO4). The Zn in ZnO has been reported to be less bioavailable for poultry compared with ZnSO4 (Sandoval et al., 1997); however, ZnSO4 is highly water soluble which can cause the breakdown of vitamins and degradation of fats, thus reducing the nutrient value of the diet (Batal et al., 2001). Other sources of trace minerals, such as hydroxychlorides, are useful in poultry diets as they may have greater bioavailability and are less reactive in feed than inorganic salts (Miles et al., 1998; Batal et al., 2001). Previous research has reported similar bioavailability of Zn from Zn hydroxychloride compared with ZnSO4 (Cao et al., 2000; Batal et al., 2001); however, research has also shown improvements in growth, meat yield, and bone breaking strength when feeding similar levels of Zn from Zn hydroxychloride compared with ZnSO4 (Olukosi et al., 2018; Nguyen et al., 2021).
New manufacturers are providing the industry with alternate suppliers of Zn hydroxychloride, and the efficacy of these new products should be evaluated. A novel Zn hydroxychloride (SAMZn) has been developed by SAM Nutrition (Bloomington, MN) and no studies have been conducted to evaluate the bioavailability of the Zn in this product for poultry. Thus, the primary objective of this study was to determine the relative bioavailability of Zn in SAMZn compared with the Zn in feed grade ZnSO4. A comparison of bone Zn responses for SAM Zn to those obtained from a commercially available source of Zn hydroxychloride (IBZn; Intellibond, Selko, Indianapolis, IN) was also included.
MATERIALS AND METHODS
General Procedures
All procedures were approved by the University of Illinois Committee on Laboratory (Animal Use Protocol 22048). A chick assay was conducted at the University of Illinois Poultry Research farm using male and female New Hampshire x Columbian Plymouth Rock/Delaware chicks. All chicks were pretested on a fully fortified corn-soybean meal diet containing 75 mg/kg supplemental Zn from ZnSO4 monohydrate for the first 3 days posthatching. All chicks were then switched to a Zn-deficient dextrose-cornstarch-soy protein concentrate basal diet until 7 days posthatching (Table 1). This diet was also the negative control diet with no supplemental Zn that was fed during the experimental period from 8 to 22 days posthatching. After an overnight feed withdrawal, chicks were weighed, wing-banded, and randomly allotted to pens such that each pen had a similar initial body weight and weight distribution.
Table 1.
Composition (as-fed basis) of the zinc-deficient basal diet.1
| Ingredient | Percentage |
|---|---|
| Soy concentrate (63.0% CP)2 | 31.00 |
| Dextrose | 36.92 |
| Cornstarch | 21.00 |
| Soybean oil | 5.00 |
| Zn-free salt mix3 | 5.37 |
| DL-Methionine | 0.20 |
| L-Threonine | 0.10 |
| Vitamin mix4 | 0.20 |
| Choline chloride (99%) | 0.20 |
| DL-α-Tocopheryl acetate | 0.002 |
| Ethoxyquin | 0.0125 |
Analyzed to contain 10.6 mg Zn/kg, 20.2% CP, 1.22% Ca, and 0.84% total P.
ADM Corp., Decatur, IL.
Provided (per kilogram of diet): Ca3(PO4)2, 28.0 g; K2HPO4, 9.0 g; NaCl, 8.89 g; MgSO4·H2O, 0.65 g; FeSO4·7H2O, 0.42 g; KI, 40 mg; CuSO4·5H2O, 20 mg; Na2MoO4·2H2O, 9 mg; H3BO3, CoSO4·7H2O, 1 mg; Na2SeO3, 0.22 mg.
Provided (per kilogram of diet): thiamine·HCl, 20 mg; niacin, 50 mg; riboflavin, 10 mg; D-Ca-pantothenate, 30 mg; vitamin B12, 0.04 mg; pyridoxine·HCl, 6 mg; D-biotin, 0.6 mg; folic acid, 4 mg; menadione dimethylpyridinol bisulfate, 2 mg; ascorbic acid, 250 mg; cholecalciferol, 15 μg; retinyl acetate, 1,789 μg.
Six replicate groups of 4 chicks (2 male and 2 female) were allowed ad libitum access to the experimental diets and water during the 14 d experimental period. Chicks were housed in heated, thermostatically controlled, stainless steel batteries (Petersime Incubator Co., Gettysburg, OH) with raised wire floors. To minimize Zn contamination from the environment, stainless steel feeders and waterers were also used. Chicks were exposed to constant fluorescent light 24 h/d.
The basal diet (Table 1) was formulated to contain approximately 20% CP and was adequate in all nutrients except Zn, which was present at an analyzed level of 10.6 mg/kg. The basal diet in Table 1 was analyzed for N, Ca, and total P at the Experiment Station Chemical Laboratories (University of Missouri, Columbia, MO) using procedures of AOAC International (2019). Treatment additions were made at the expense of cornstarch. Upon termination of the experiment, chicks and feeders were weighed, and chicks were euthanized with carbon dioxide gas. The right tibia bone was removed, autoclaved, cleaned of adhering tissue, and ashed in a muffle furnace. The basal diet, diets containing 10 to 15 mg/kg supplemental Zn, the feed grade ZnSO4, SAMZn, IBZn, and ashed bones were sent to the Experiment Station Chemical Laboratories (University of Missouri, Columbia, MO) for Zn analysis using optical emission spectroscopy according to AOAC procedures (AOAC International, 2019).
Chick Assay
The Zn-deficient basal diet was supplemented with 0, 7, 15 mg/kg Zn from feed grade ZnSO4 monohydrate (analyzed Zn = 35.5%) to establish a standard response curve. The same basal diet was supplemented with 3, 7, and 10 mg/kg Zn from SAMZn (analyzed Zn = 58%) and 10 mg/kg Zn from IBZn (analyzed Zn = 55%). The last dietary treatment was included to provide a comparison between the new SAMZn and a commercially available source of Zn hydroxychloride. Weight gain, feed intake, and feed efficiency (gain: feed) were calculated for each pen of chicks. Total tibia ash content (mg/tibia) and concentration (%) were calculated. In addition, supplemental Zn intake, tibia ash Zn concentration, and total tibia Zn were calculated. Total tibia Zn was then evaluated as a function of supplemental Zn intake, and multiple regression slope-ratio methodology was used to calculate a relative bioavailability value (RBV) for both sources of Zn hydroxychloride as described below. The levels of supplemental Zn from SAMZn were lower than those from ZnSO4 in attempt to ensure that tibia Zn responses to SAMZn would be within the boundaries of the ZnSO4 standard response curve (i. e., not exceed it) because it was expected that the bioavailability of the Zn in SAMZn might be higher than the Zn in ZnSO4.
Statistical Analysis
Pen means were subjected to ANOVA procedures for a completely randomized design in SAS (SAS Institute; Cary, NC) and then the least significant difference (LSD) procedure of SAS was used to establish differences among individual treatment means. The RBV was determined using slope-ration methodology (Finney, 1978). The multiple linear regression model consisted of 2 regression lines with a common intercept. The dependent variable, total tibia Zn, was regressed on supplemental Zn intake from ZnSO4 and SAMZn. The RBV was calculated by dividing the regression coefficient in the multiple linear regression equation for SAMZn by the regression coefficient for ZnSO4. Significance was determined at P < 0.05. The calculated dietary levels of added or supplemental Zn were used for the regression in the regression analysis.
RESULTS AND DISCUSSION
The basal diet (Table 1) was analyzed to contain 20.2% CP, 1.22% Ca, 0.84% total P, and 10.6 mg/kg Zn. The diets containing 15 mg/kg supplemental Zn from ZnSO4 or 10 mg/kg supplemental Zn from SAMZn or IBZn were analyzed to contain 31.9, 20.1, and 25.5 mg/kg Zn, respectively. These values agreed reasonably well with the calculated levels of 25.6, 20.6, and 20.6 mg/kg, respectively.
Growth Parameters
Weight gain increased by a maximum of 100% (P < 0.05) with increasing dietary Zn concentration from the Zn sources (Table 2). Previous research demonstrated similar weight gain improvements as Zn was added to a Zn-deficient soy concentrate diet (Batal et al., 2001). Interestingly, the weight gain of chicks fed 7 or 10 mg Zn/kg from SAMZn or 10 mg Zn/kg from IBZn was similar (P > 0.05) to chicks fed the diet containing 15 mg Zn/kg from ZnSO4 (Table 2). Similarly, M'Sadeq et al. (2018) reported higher (P < 0.05) weight gain when broiler chickens were fed diets supplemented with Zn hydroxychloride at a Zn concentration lower than the inorganic Zn level in the basal diet. Feeding either source of Zn hydroxychloride (SAMZn and IBZN) at 10 mg Zn/kg resulted in similar (P > 0.05) weight gains.
Table 2.
Growth and bone analysis responses to increasing levels of Zn.1
| Supplemental Zn |
||||||||
|---|---|---|---|---|---|---|---|---|
| Source2 | Level, mg/kg | Intake, mg | Weight gain, g | Feed intake, g | Gain:feed, g/kg | Tibia ash Zn, μg/g bone ash | Total tibia Zn, μg3 | Zn RBV, %4 |
| — | 0 | 0.00 | 146e | 305e | 477d | 56.9e | 20.9e | – |
| FG ZnSO4 | 7 | 2.89 | 247c | 413c | 597b | 77.3d | 39.9c | – |
| FG ZnSO4 | 15 | 6.99 | 281ab | 466a | 602b | 119.5a | 65.4a | 100b |
| Zn hydroxychloride (SAMZn) | 3 | 1.14 | 205d | 381d | 537c | 71.5d | 30.9d | – |
| Zn hydroxychloride (SAMZn) | 7 | 3.06 | 271b | 437bc | 620ab | 83.9c | 44.0c | – |
| Zn hydroxychloride (SAMZn) | 10 | 4.45 | 290a | 446ab | 653a | 102.4b | 53.4b | 115a |
| Zn hydroxychloride (IBZn) | 10 | 4.57 | 292a | 458ab | 639a | 96.6b | 52.4b | |
| Pooled SEM | 0.079 | 5.5 | 9.1 | 11.7 | 2.19 | 1.57 | ||
Means within a column with no common superscripts differ (P < 0.05).
Data are means of 6 pens of 4 chicks (2 male, 2 female) fed the experimental diets for 14 d (d 8–d 22 posthatching).
Feed-grade (FG) ZnSO4 contained 35.5% Zn, Zn hydroxychloride sources contained 58% Zn (SAMZn) and 55% Zn (IBZn).
Multiple linear regression of total tibia Zn (Y, μg) on supplemental Zn intake (X, mg) was Y = 21.72 + 6.25 ± 0.27 X1 + 7.20 ± 0.40 X2, R2 = 0.95, where X1 = FG ZnSO4 and X2 = SAMZn.
Relative bioavailability value (RBV) for SAMZn was calculated by dividing the regression coefficient in the multiple regression equation for SAMZn by the regression coefficient for ZnSO4. Statistical difference between RBV values is based on significance of differences between the regression coefficients in the multiple regression equation in footnote 3.
Feed intake increased by a maximum of 53% (P < 0.05) with increasing dietary Zn concentrations. Similar to weight gain, feed intake of chicks fed 10 mg Zn/kg from either Zn hydroxychloride source was similar (P > 0.05) to chicks consuming the diet containing 15 mg Zn/kg from ZnSO4. The gain: feed ratio generally increased (maximum increase of 37%) with increasing Zn supplementation. Chicks fed 10 mg Zn/kg from either Zn hydroxychloride source had a higher gain: feed ratio (P < 0.05) when compared with chicks fed either level of ZnSO4. Olukosi et al. (2018) reported a significantly greater gain: feed ratio in broiler chickens fed Zn hydroxychloride compared with ZnSO4. Additionally, M'Sadeq et al. (2018) reported a greater (P < 0.05) gain: feed ratio when broiler chickens were fed diets supplemented with Zn hydroxychloride compared with a diet supplemented with inorganic Zn.
Bone Analysis
Tibia ash Zn concentration and total tibia Zn increased (P < 0.05) with increasing supplemental Zn, regardless of source (maximum increase of 110 and 213%, respectively). These data agree with another study using a Zn-deficient basal diet to establish a RBV (Batal et al., 2001). Both tibia ash Zn concentration and total tibia Zn were not different (P > 0.05) for chicks fed 10 mg Zn/kg from either source of Zn hydroxychloride. Tibia ash Zn concentration was greater (P > 0.05) for chicks fed 7 mg/kg Zn from SAMZn compared with chicks fed the same level of Zn from ZnSO4.
Regression Analysis
Total tibia Zn (Y, μg/tibia) regressed on supplemental Zn intake (X, mg) yielded the multiple linear regression equation: Y = 21.72 + 6.25 ± 0.27 X1 + 7.21 ± 0.40 X2 (R2 = 0.95; Table 2), where X1 = ZnSO4 and X2 = SAMZn. Using this equation, the RBV for ZnSO4 and SAMZn were calculated to be 100 and 115%, respectively. The RBV of SAMZn was higher (P < 0.05) than ZnSO4. Research by Cao et al. (2000) and Batal et al. (2001) reported no significance difference in RBV estimates of Zn hydroxychloride relative to ZnSO4. Both of those studies used analytical-grade ZnSO4, whereas the current study utilized feed grade ZnSO4. Batal et al. (2001) hypothesized if they had used feed grade ZnSO4, the RBV of their source of Zn hydroxychloride would have been higher at an estimated 122% relative to feed grade ZnSO4. Possible reasons for the higher relative bioavailability of Zn in SAMZN in the current study are 1) manufacturing procedures which yield smaller particle size, increased surface area, thereby possibly improving intestinal absorption of the Zn, 2) a manufacturing procedure which results in only marginal solubility in water but complete solubility in weak acid so that it dissolves more slowly in the digestive tract and increases its release at the absorptive sites in the small intestine, and 3) upregulation of gene expression of tight junction proteins in the jejunum (Miles et al., 1998; Nguyen et al., 2021; Olukosi et al., 2018).
The RBV of the 2 Zn sources herein was determined using a soy protein concentrate diet. Wedekind et al. (1992) reported that type of diet may influence RBV of different Zn sources. They determined bioavailability of Zn in Zn-methionine relative to ZnSO4 using 3 different diets which were purified crystalline amino acid, semi purified soy isolate, and corn soybean meal diets. The results showed numerical differences in RBV of Zn among diets with the major difference being between the purified crystalline amino acid diet and the other 2 diets. We used a soy protein concentrate diet herein, which is most similar to the soy isolate diet used by Wedekind et al. (1992). The soy concentrate diet was used in the current study because it is more deficient in Zn than a corn soybean meal diet so it is more sensitive and responsive to added Zn. The soy concentrate diet also yields a large growth response to added Zn (Table 2) whereas a corn soybean meal diet generally yields little or no growth response to added Zn (Wedekind et al.,1992).
In conclusion, the results of this study indicated that the bioavailability of Zn (based on tibia ash) in SAMZn was relatively higher than bioavailability of Zn in feed grade ZnSO4. The study also demonstrated that, based on tibia Zn responses to 10 mg/kg supplemental Zn, bioavailability of Zn in SAMZn was similar to that in the commercially available Zn hydroxychloride source IBZn.
DISCLOSURES
There is no conflict of interest on manuscript.
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