Abstract

Phosphorus is essential for the growth of poultry, particularly for bone development. Eighty percent or more of the total P is in the form of phytate. Monogastrics, such as chickens and pigs, do not secrete the enzyme that breaks down phytates and separates P in grains or oil meals. Organic acids (OA) effectively check the growth of mold and bacteria. Furthermore, adding OA to feed can lower the gastric pH. Low gastric pH accelerates the conversion of pepsinogen to pepsin, which improves the absorption rate of proteins, amino acids, and minerals. This experiment was performed to examine the effect of adding OA to feeds with different available P (AP) levels in terms of egg productivity, egg quality, and IgY levels. Results suggest that the AP level in feed does not have to be higher than 0.3%, when compared with 0.4% AP in the diet. Supplementation of 0.2% OA to the 0.3% AP diet showed the best results in hen-housed egg production, soft-shell plus broken egg production, FCR, and egg yolk IgY. However, the best eggshell color was obtained in the 0.4% AP and 0.2% OA diet.

Primary Audience: Poultry Nutritionists, Commercial Producers, Researchers

DESCRIPTION OF PROBLEM

Phosphorus is essential for the growth of poultry, particularly for bone development. Poultry feeds are usually produced on a corn-soybean meal basis. Although a corn-soybean meal diet has a higher P content than other grains, 80% or more of the total P is in the form of phytic acid or phytate. Monogastrics such as chickens and pigs do not secrete the enzyme that breaks down phytates and separates P in grains or oil meals. Thus, organic P that is usable (available) to poultry is very limited [1, 2]. Therefore, dietary supplementation of available P (AP) in the form of nonphytate or inorganic P, which is available close to 100%, is essential. The NRC [3] specifies that laying hens need 0.25% nonphytin P (based on 100 g of feed/d), but this is the minimum requirement. To be safe, feed plants and poultry farms are using 0.3 to 0.4% AP formulas because of the uncertain content of nonphytate P. However, the addition of inorganic P for safety is costly. Moreover, modern poultry farming is managed intensively and a large P content in poultry manure poses an obstacle to the development of the poultry farming industry [4, 5].

Meanwhile, intense poultry farming increases disease propagation [6]. For example, endogenous respiratory diseases such as low pathogenic avian influenza and infectious bronchitis are causing the poultry industry many losses by lowering egg productivity, making eggshell color lighter, and increasing broken-egg production [7]. Organic acids (OA), which are generated from the animals, plants, or microorganisms in nature, are known to check harmful microorganisms in the respiratory and digestive organs of poultry. Approximately 60 OA classes have been reported, including lactic acid, citric acid, formic acid, fumaric acid, and various mixed agents. Organic acids have been used for food preservatives because they prevent the proliferation of pathogenic microorganisms in carcasses; as such, they are used during the processing of broilers [8]. Hwang and Beuchat [9] reported that feed with OA effectively checked the growth of mold and bacteria. Furthermore, adding OA to feed can lower the gastric pH [10, 11]. Low gastric pH accelerates the conversion of pepsinogen to pepsin, which improves the absorption rate of proteins, amino acids, and minerals [12–14]. Because of the biochemical characteristics of OA, they permeate the cell membranes of pathogenic bacteria and lower the pH value inside the cells. This kills pathogenic bacteria through the depletion of metabolic energy, the decline of cell membrane metabolism, the outflow of cell fluids, and the blockage of the use of nutrients [15]. To study the influence of dietary AP and OA, therefore, a feeding experiment was conducted to investigate their effects on the productivity and egg quality of laying hens.

MATERIALS AND METHODS

Experimental Diets

The basal diet contained 16.0% CP and 2,760 kcal/kg of ME (Table 1). Other nutrients followed NRC (1994) [3] recommendations. The experiment was performed with 4 dietary treatments: AP 0.3% + OA 0.0% (AP 0.3 + OA 0.0), AP 0.3 + OA 0.2, AP 0.4 + OA 0.0, and AP 0.4 + OA 0.2. According to treatment, experimental diets were prepared with an AP content of 0.3 or 0.4% each, to which 0 or 0.2% OA was added (Table 1). Adjustment of AP was made by using dicalcium phosphate, and the OA was a commercial product, Lactacid [16], which is a 64% composite OA product. The OA treatment was supplemented with Lactacid at the 0.2% level, which provides 1,280 ppm of OA in Ca salt form. All feeds contained 0.5 mg of phytase/kg of diet, or 0.01% Phytase-5000 [17]. The feeds were mixed at 7-d intervals to maintain stability. Trace raw materials were premixed with a premixer, and the test feeds were mixed for 10 min in a vertical mixer with a 200-kg capacity.

Test Design, Test Period, and Feeding Method

The test animals were 1,216 Hy-Line Brown [18] 75-wk-old laying hens. Hens were fed a commercial layer diet (16.0% CP) until they were used for the experiment. To assign them into 4 treatments of 8 replications, they were housed in 2 units of 2-line and 2-tier A-shaped cage stands totaling 8 lines. Each line (block) was repeated with 4 treatments per block, 19 cages per treatment, and 2 birds per cage, totaling 152 birds (4 treatments × 19 cages × 2 birds) per line or 304 birds (8 replications × 19 cages × 2 birds) per treatment. Water and feed were given ad libitum, and the lighting cycle was fixed at 16L:8D. The feeding test period was 6 wk (42 d), and the average indoor temperature during the test period was 21°C.

Measurements

Productivity.

To evaluate productivity, hen-day egg production (number of eggs/number of live birds × 100), hen-housed egg production (number of eggs/number of birds housed × 100), egg weight, soft-shell plus broken eggs, ADFI, FCR, and mortality were measured. Egg production was measured at 1600 h every day after egg collection. The mean egg weight was measured by the weekly average weight of eggs, excluding abnormal eggs (soft-shell plus broken eggs). The ADFI was measured once per week (ADFI = supply quantity − remainder). The FCR was calculated by the grams of ADFI per gram of egg mass.

Egg Quality.

To evaluate egg quality, we randomly selected 320 eggs/wk (10 per replication, 80 per treatment) for examination of eggshell strength, eggshell thickness, eggshell color, yolk color, and Haugh units (HU). The measurements were taken once per week, 7 times in total (0, 1, 2, 3, 4, 5, and 6 wk). Eggshell strength was measured using a texture analyzer [19], and the eggshell thickness was measured using a dial pipe gauge [20]. The HU were calculated by the formula HU = 100 log[H −(1.7 × W0.37 + 7.57)] [21], where W refers to measurements of egg weight (g) and H refers to albumen height (mm), using an HU measuring instrument [22]. The eggshell color and yolk color were measured using color fans [23]. To measure the IgY inside the yolk, we removed the albumen with tissue paper in accordance with the method of Hatta [24, 25]. After removing the yolk membrane, the yolks were pooled and mixed. The yolk mixture was kept cool (2 to 8°C). On the measurement day, 5 g of yolk was diluted with 5 mL (1:1) of distilled water and then homogenized for 30 s with a homogenizer. Next, 20 mL of 0.1% λ-carrageenan was added and fixed for 30 min. After that, the mixture was centrifuged for 15 min at 7,000 × g to obtain the water-soluble fraction and was diluted (1:20,000). The IgY level in the water-soluble fraction of the yolk was measured using the sandwich ELISA method. For the IgY standard reference value, the chicken IgY [26] was measured using 25, 50, 100, 250, 500, and 1,000 ng/mL. The values were converted using a regression equation for each measurement.

Statistical Processing

A factorial analysis was conducted to test main effects (AP and OA) and their interactions using the SAS [27] statistics application of the 2-way ANOVA procedure. If F-test results were significant, differences in means among treatment groups were separated by the LSMEANS procedure with the Tukey option by using GLM [27].

RESULTS AND DISCUSSION

Productivity

The productivity data of laying hens, including hen-day and hen-housed egg production, egg weight, soft-shell plus broken egg production, ADFI, and FCR are summarized in Table 2. There were no significant differences in hen-day egg production. However, AP levels significantly affected hen-housed egg production and a significant interaction existed between AP and OA. Hen-housed egg production was significantly higher in the AP 0.3 treatment group than in the AP 0.4 treatment group. Hen-day egg production was higher in the AP 0.3 + OA 0.2 treatment group than in the AP 0.4 + OA 0.0 treatment group, but was not significantly different from the AP 0.3 + OA 0.0 and the AP 0.4 + OA 0.2 treatment groups. There were no significant differences in egg weight among treatment groups. Soft-shell plus broken egg production decreased significantly, from 0.34 to 0.17%, when OA was added. The ratio of soft-shell plus broken egg production was small but the reduction in OA-supplemented groups was significant.

Available P or OA did not significantly affect ADFI. The FCR significantly decreased with the addition of 0.2% OA. The AP × OA interaction was significant as well. The FCR was lowest in the AP 0.3 + OA 0.2 treatment group, followed by the AP 0.4 + OA 0.2, AP 0.3 + OA 0.0, and AP 0.4 + OA 0.0 treatment groups. Available P or OA did not significantly affect mortality. Although the NRC [3] minimum requirement for nonphytate P in laying hens is 0.25%, the feed industry uses 0.3 to 0.4% because the lack of nonphytate P has a great influence on egg-laying productivity. According to the above results, decreasing the level of nonphytate P (or AP) from 0.4 to 0.3% did not decrease productivity at all. On the contrary, the AP 0.3 treatments were higher than the AP 0.4 treatments in hen-housed egg production. Boling-Frankenbach et al. [28] investigated the effect of OA addition according to the AP level and found that lowering the AP level (0.2% or less) and feeding OA decreased productivity, hen-day egg production, and the FCR. But supplementation of OA when the AP level was at 0.2% or higher improved productivity and FCR, similar to the results of the present experiment. Sohil and Roland [29] investigated the effect of P content in feed in Hy-Line W36 laying hens and found that increasing the level of AP (0.1 to 0.7%) significantly increased hen-housed egg production. However, AP levels at 0.3 to 0.4% did not produce significant differences in hen-housed egg production, similar to the results of this experiment. The addition of OA probably improved hen-housed egg production by decreasing soft-shell plus broken egg production, FCR, and mortality, which were not statistically significant. A possible explanation for the low soft-shell plus broken egg production is that OA in Ca salt form may have provided some extra Ca, or OA may have improved mineral absorption for shell formation [13]. Dhawale [30] reported that feeding OA lowered the production of soft-shell plus broken eggs and coarse-surface eggs. Soltan [31] conducted an experiment with supplementary OA at 260, 520, and 780 ppm and found that egg production (hen-day) of the 780-ppm treatment group was significantly higher than egg production in the control and other treatment groups. Although egg weight and ADFI were not different, Son et al. [32] reported that adding OA to the diet slowed the passage of feed through the digestive organs and that the increased digestion time improved the chickens’ use of nutrients. Izat et al. [33] reported that adding OA to the broiler diet improved productivity, and Woo et al. [34] reported that it decreased ADFI and FCR. However, Park et al. [35] reported that supplementary OA showed no significant differences in ADFI and FCR. In addition to the above results, many studies [36–40] reported that OA inhibited the proliferation of harmful bacteria in the intestines and increased the digestive absorption and use of nutrients in the feed.

Egg Quality

The eggshell color, yolk color, eggshell strength, eggshell thickness, HU, and IgY content are summarized in Table 3. As shown in the table, there were no significant differences in yolk color, eggshell strength, eggshell thickness, and HU among treatment groups. However, the interaction between AP and OA regarding the eggshell color (brown level) was significant. The AP 0.4 + OA 0.2 treatment group had significantly higher chromaticity than the other treatment groups. The pigments for brown eggshell is porphyrin, which is derived from blood hemoglobin. De novo synthesis of pigments may occur in the shell gland pouch [41]. Supplementation of OA may improve the integrity of the reproductive organs, such as the shell gland in the oviduct, resulting in an improvement in eggshell color. Park et al. [35] found that the eggshell strength and HU increased with OA treatment, which was different from the findings of this study. They also investigated yolk color and found that treatment with OA did not produce significant differences, which agrees with the results of the present experiment. The IgY levels significantly increased with the addition of OA, which seems related to the earlier finding [42] that adding OA to feed influences the digestive mucous membrane and improves immune function. However, more studies may be needed to verify the effects of OA on the IgY level and immune properties of poultry.

CONCLUSIONS AND APPLICATIONS

  1. Hen-housed egg production was improved with 0.3% AP compared with 0.4% AP. Soft-shell plus broken egg production and FCR were improved by OA. Hen-housed egg production was highest in the AP 0.3 + OA 0.2 treatment group and FCR was lowest in the AP 0.3 + OA 0.2 group.

  2. Chromaticity of brown eggshells was highest in the AP 0.4 + OA 0.2 group and IgY level of the egg yolk was increased by OA supplementation.

  3. Based on the production performance of hen-housed egg production and FCR, 0.3% AP in the layer diet was better than 0.4% AP. Supplementation with OA at the level of 0.2% showed better results in soft-shell plus broken egg production, FCR, and IgY concentration in egg yolks.

  4. In conclusion, addition of composite OA to the layer diet is beneficial. Dietary inorganic P at the level of 0.3% is sufficient for 75- to 80-wk-old layers.

Table 1

Formula and composition of layer diets with different available P (AP) and supplemental organic acids (OA)

Item AP 0.3% + OA 0.0% AP 0.3% + OA 0.2% AP 0.4% + OA 0.0% AP 0.4% + OA 0.2% 
1Rhodimet (methionine hydroxy analog 88%, liquid, Adisseo Co., Antony, France). 
2Vitamin premix provided (per kg of diet): vitamin A, 13,500 IU; vitamin D3, 3,150 IU; vitamin E, 22.5 IU; menadione, 3.0 mg; vitamin B12, 0.0225 mg; riboflavin, 6.0 mg; pantothenic acid, 12.75 mg; niacin, 30 mg; thiamine, 2.25 mg; pyridoxine, 4.5 mg; folic acid, 0.9 mg; biotin, 0.1155 mg. 
3Mineral premix provided (per kg of diet): copper, 5.25 mg; iodine, 0.9 mg; iron, 60 mg; manganese, 82.5 mg; selenium, 0.195 mg; zinc, 75 mg. 
4Phytase-5000 [5,000 μg/g (phytase/powder), Fujian Fuda Biotech Co., Fuzhou City, Fujian, P. R. China]. 
5Sintox [toxin binder (SiO2 48.0%, Al2O3 18.0%), ENT Co., Daejeon-si, Korea]. 
6Lactacid (Ca-formate 17%, Ca-propionate 5%, Ca-lactate 15%, citric acid 27%, and carrier 36%), Eunjin Bio. Co., Cheonan-si, Korea. 
Ingredient, % 
    Corn, ground (US no. 3) 61.71 61.71 61.44 61.44 
    Soybean meal (44%, local) 18.40 18.40 18.40 18.40 
    Rapeseed meal 1.50 1.50 1.50 1.50 
    Perilla meal 2.50 2.50 2.50 2.50 
    Corn gluten meal 2.78 2.78 2.78 2.78 
    Animal fat 2.18 2.18 2.18 2.18 
    Salt, dehydrated 0.20 0.20 0.20 0.20 
    Dicalcium phosphate (18.5% P) 1.00 1.00 1.60 1.60 
    Limestone (2 mm) 9.08 9.08 8.75 8.75 
    Rhodimet1 (88%, liquid) 0.11 0.11 0.11 0.11 
    Choline chloride (50%, liquid) 0.08 0.08 0.08 0.08 
    Vitamin premix2 0.15 0.15 0.15 0.15 
    Mineral premix3 0.15 0.15 0.15 0.15 
    Phytase-50004 0.01 0.01 0.01 0.01 
    Sintox5 0.15 0.15 0.15 0.15 
    Lactacid6 — 0.20 — 0.20 
    Total 100.0 100.2 100.0 100.2 
Calculated composition, % 
    ME, kcal/kg 2,760 2,760 2,760 2,760 
    CP 16.00 16.00 16.00 16.00 
    Fat 4.63 4.63 4.63 4.63 
    Fiber 2.77 2.77 2.77 2.77 
    Ash 13.05 13.13 13.05 13.13 
    Ca 3.80 3.88 3.80 3.88 
    Available P 0.30 0.30 0.40 0.40 
Item AP 0.3% + OA 0.0% AP 0.3% + OA 0.2% AP 0.4% + OA 0.0% AP 0.4% + OA 0.2% 
1Rhodimet (methionine hydroxy analog 88%, liquid, Adisseo Co., Antony, France). 
2Vitamin premix provided (per kg of diet): vitamin A, 13,500 IU; vitamin D3, 3,150 IU; vitamin E, 22.5 IU; menadione, 3.0 mg; vitamin B12, 0.0225 mg; riboflavin, 6.0 mg; pantothenic acid, 12.75 mg; niacin, 30 mg; thiamine, 2.25 mg; pyridoxine, 4.5 mg; folic acid, 0.9 mg; biotin, 0.1155 mg. 
3Mineral premix provided (per kg of diet): copper, 5.25 mg; iodine, 0.9 mg; iron, 60 mg; manganese, 82.5 mg; selenium, 0.195 mg; zinc, 75 mg. 
4Phytase-5000 [5,000 μg/g (phytase/powder), Fujian Fuda Biotech Co., Fuzhou City, Fujian, P. R. China]. 
5Sintox [toxin binder (SiO2 48.0%, Al2O3 18.0%), ENT Co., Daejeon-si, Korea]. 
6Lactacid (Ca-formate 17%, Ca-propionate 5%, Ca-lactate 15%, citric acid 27%, and carrier 36%), Eunjin Bio. Co., Cheonan-si, Korea. 
Ingredient, % 
    Corn, ground (US no. 3) 61.71 61.71 61.44 61.44 
    Soybean meal (44%, local) 18.40 18.40 18.40 18.40 
    Rapeseed meal 1.50 1.50 1.50 1.50 
    Perilla meal 2.50 2.50 2.50 2.50 
    Corn gluten meal 2.78 2.78 2.78 2.78 
    Animal fat 2.18 2.18 2.18 2.18 
    Salt, dehydrated 0.20 0.20 0.20 0.20 
    Dicalcium phosphate (18.5% P) 1.00 1.00 1.60 1.60 
    Limestone (2 mm) 9.08 9.08 8.75 8.75 
    Rhodimet1 (88%, liquid) 0.11 0.11 0.11 0.11 
    Choline chloride (50%, liquid) 0.08 0.08 0.08 0.08 
    Vitamin premix2 0.15 0.15 0.15 0.15 
    Mineral premix3 0.15 0.15 0.15 0.15 
    Phytase-50004 0.01 0.01 0.01 0.01 
    Sintox5 0.15 0.15 0.15 0.15 
    Lactacid6 — 0.20 — 0.20 
    Total 100.0 100.2 100.0 100.2 
Calculated composition, % 
    ME, kcal/kg 2,760 2,760 2,760 2,760 
    CP 16.00 16.00 16.00 16.00 
    Fat 4.63 4.63 4.63 4.63 
    Fiber 2.77 2.77 2.77 2.77 
    Ash 13.05 13.13 13.05 13.13 
    Ca 3.80 3.88 3.80 3.88 
    Available P 0.30 0.30 0.40 0.40 
Table 2

Effect of level of available P (AP) and supplemental organic acids (OA) on productivity of laying hens1

Diet Hen-day egg production, % Hen-housed egg production, % Egg weight, g Soft-shell plus broken eggs, % ADFI, g FCR2 Mortality, % 
a–dMeans with the different superscripts in the same column differ significantly (P < 0.05). 
A–DMeans with the different superscripts in the same column differ significantly (P < 0.01). 
1Data are reported as least squares means measured during 75 to 80 wk of age. 
2FCR = average daily feed intake/egg mass (g/g). 
AP 
    0.3% 75.2 74.86c 66.1 0.26 111.7 2.25 1.13 
    0.4% 73.2 72.44d 66.4 0.25 110.4 2.28 1.50 
OA 
    0.0% 73.3 72.54 66.3 0.34A 112.1 2.32C 1.64 
    0.2% 75.2 74.76 66.2 0.17B 110.0 2.22D 0.99 
AP × OA 
    0.3% × 0.0% 74.4 73.79ab 66.3 0.35 113.3 2.30ab 1.60 
    0.3% × 0.2% 76.1 75.92a 65.9 0.16 110.1 2.20b 0.66 
    0.4% × 0.0% 72.2 71.28b 66.2 0.33 111.0 2.33a 1.69 
    0.4% × 0.2% 74.3 73.59ab 66.5 0.17 109.9 2.23ab 1.32 
Pooled SEM 3.148 1.582 0.274 0.176 3.019 0.088 1.743 
Source of variation ——— P > F ——— 
    AP 0.0866 0.0444 0.2906 0.9203 0.2734 0.4225 0.6440 
    OA 0.1020 0.0669 0.7642 0.0075 0.0565 0.0024 0.4163 
    AP × OA 0.1256 0.0486 0.3980 0.0723 0.1215 0.0211 0.8089 
Diet Hen-day egg production, % Hen-housed egg production, % Egg weight, g Soft-shell plus broken eggs, % ADFI, g FCR2 Mortality, % 
a–dMeans with the different superscripts in the same column differ significantly (P < 0.05). 
A–DMeans with the different superscripts in the same column differ significantly (P < 0.01). 
1Data are reported as least squares means measured during 75 to 80 wk of age. 
2FCR = average daily feed intake/egg mass (g/g). 
AP 
    0.3% 75.2 74.86c 66.1 0.26 111.7 2.25 1.13 
    0.4% 73.2 72.44d 66.4 0.25 110.4 2.28 1.50 
OA 
    0.0% 73.3 72.54 66.3 0.34A 112.1 2.32C 1.64 
    0.2% 75.2 74.76 66.2 0.17B 110.0 2.22D 0.99 
AP × OA 
    0.3% × 0.0% 74.4 73.79ab 66.3 0.35 113.3 2.30ab 1.60 
    0.3% × 0.2% 76.1 75.92a 65.9 0.16 110.1 2.20b 0.66 
    0.4% × 0.0% 72.2 71.28b 66.2 0.33 111.0 2.33a 1.69 
    0.4% × 0.2% 74.3 73.59ab 66.5 0.17 109.9 2.23ab 1.32 
Pooled SEM 3.148 1.582 0.274 0.176 3.019 0.088 1.743 
Source of variation ——— P > F ——— 
    AP 0.0866 0.0444 0.2906 0.9203 0.2734 0.4225 0.6440 
    OA 0.1020 0.0669 0.7642 0.0075 0.0565 0.0024 0.4163 
    AP × OA 0.1256 0.0486 0.3980 0.0723 0.1215 0.0211 0.8089 
Table 3

Effect of level of available P (AP) and supplemental organic acids (OA) on egg quality of laying hens1

Diet Shell color Yolk color Shell strength, kg/cm2 Shell thickness, 10−2 mm Haugh unit2 IgY, mg/mL 
a,bMeans with the different superscripts in the same column differ significantly (P < 0.05). 
1Data are reported as least squares means measured from 75 to 80 wk of age. 
2Haugh unit = 100 log[H −(1.7 × W0.37 + 7.57)], where H is albumen height (mm) and W is egg weight (g). 
AP 
    0.3% 11.15 8.65 2.85 40.1 78.5 9.48 
    0.4% 11.34 8.68 2.87 40.2 79.3 9.38 
OA 
    0.0% 11.15 8.66 2.82 40.1 79.2 9.08b 
    0.2% 11.33 8.66 2.90 40.2 78.6 9.78a 
AP × OA 
    0.3% × 0.0% 11.11b 8.65 2.82 39.9 79.0 9.17 
    0.3% × 0.2% 11.19b 8.64 2.88 40.3 78.1 9.80 
    0.4% × 0.0% 11.19b 8.66 2.81 40.3 79.3 8.99 
    0.4% × 0.2% 11.49a 8.69 2.92 40.0 79.2 9.77 
Pooled SEM 0.272 0.097 0.211 0.639 1.527 0.513 
Source of variation ——— P > F ——— 
    AP 0.0703 0.3661 0.8537 0.8771 0.1710 0.1996 
    OA 0.0713 0.8981 0.2491 0.8642 0.3537 0.0496 
    AP × OA 0.0472 0.8061 0.6927 0.4673 0.3583 0.2892 
Diet Shell color Yolk color Shell strength, kg/cm2 Shell thickness, 10−2 mm Haugh unit2 IgY, mg/mL 
a,bMeans with the different superscripts in the same column differ significantly (P < 0.05). 
1Data are reported as least squares means measured from 75 to 80 wk of age. 
2Haugh unit = 100 log[H −(1.7 × W0.37 + 7.57)], where H is albumen height (mm) and W is egg weight (g). 
AP 
    0.3% 11.15 8.65 2.85 40.1 78.5 9.48 
    0.4% 11.34 8.68 2.87 40.2 79.3 9.38 
OA 
    0.0% 11.15 8.66 2.82 40.1 79.2 9.08b 
    0.2% 11.33 8.66 2.90 40.2 78.6 9.78a 
AP × OA 
    0.3% × 0.0% 11.11b 8.65 2.82 39.9 79.0 9.17 
    0.3% × 0.2% 11.19b 8.64 2.88 40.3 78.1 9.80 
    0.4% × 0.0% 11.19b 8.66 2.81 40.3 79.3 8.99 
    0.4% × 0.2% 11.49a 8.69 2.92 40.0 79.2 9.77 
Pooled SEM 0.272 0.097 0.211 0.639 1.527 0.513 
Source of variation ——— P > F ——— 
    AP 0.0703 0.3661 0.8537 0.8771 0.1710 0.1996 
    OA 0.0713 0.8981 0.2491 0.8642 0.3537 0.0496 
    AP × OA 0.0472 0.8061 0.6927 0.4673 0.3583 0.2892 
1
Present address: Department of R& D, Nong- Hyup Feed Inc., Seoul, 134–763, South Korea.

Nong- Hyup Feed Inc., Seoul, Korea, provided the funding for this research.

REFERENCES AND NOTES

1
Jongbloed
,
A. W.
, and N. P. Lenis.
1998
. Environmental concerns about animal manure.
J. Anim. Sci.
 
76
:
2641
–2648.
2
Abelson
,
P. H.
1999
. A potential phosphate crisis.
Science
 
283
:
2015
.
3
NRC.
1994
. Nutrient Requirements of Poultry. 9th rev. ed. Natl. Acad. Press, Washington, DC.
4
Camus
,
M. C.
, and J. C. Laporte.
1976
. Inhibition de la protéolyse pepsique in vitro par le blé. Rôle de l’acide phytique des issues.
Ann. Biol. Anim. Biochem. Biophys.
 
16
:
719
–729.
5
Singh
,
M.
, and A. D. Krikorian.
1982
. Inhibition of trypsin activity in vitro by phytate.
J. Agric. Food Chem.
 
30
:
799
–800.
6
Anadon
,
A.
, and M. R. Larranaga.
1999
. Residues of antimicrobial drugs and feed additives in animal products: Regulatory aspects.
Livest. Prod. Sci.
 
59
:
183
–198.
7
Song
,
J. H.
, B. J. Woo, D. Huh, and S. I. Park.
2006
. An economic analysis of livestock disease.
Korea Rur. Econ. Inst. Res. Rev.
 
6-0007
(R519):
47
–56.
8
Higgins
,
C.
, and F. Brinkhaus.
1999
. Efficacy of several organic acids against molds.
J. Appl. Poult. Res.
 
8
:
480
–487.
9
Hwang
,
C. A.
, and L. R. Beuchat.
1995
. Efficacy of a lactic acid/sodium benzoate wash solution in reducing bacterial contamination of raw chicken.
Int. J. Food Microbiol.
 
27
:
91
–98.
10
Ravindran
,
V.
, and E. T. Kornegay.
1993
. Acidification of weaner pig diets: A review.
J. Sci. Food Agric.
 
62
:
313
–322.
11
Garrido
,
M. N.
, M. Skjervheim, H. Oppegaard, and H. Sorum.
2004
. Acidified litter benefits the intestinal flora balance of broiler chickens.
Appl. Environ. Microbiol.
 
70
:
5208
–5213.
12
Jongbloed
,
A. W.
, P. A. Kemme, Z. Morz, and H. T. M. Van Diepen.
2000
. Efficacy, use and application of microbial phytase in pig production: A review. Pages 111–129 in Biotechnology in the Feed Industry, Proc. Alltech’s 16th Annu. Symp. T. P. Lyons, and K. A. Jacques, ed. Nottingham Univ. Press, Nottingham, UK.
13
Omogbenigun
,
F. O.
, C. M. Nyachoti, and B. A. Slominski.
2003
. The effects of supplementing microbial phytase and organic acids to a corn-soybean based diet fed to early-weaned pigs.
J. Anim. Sci.
 
81
:
1806
–1813.
14
Youn
,
B. S.
, K. T. Nam, K. M. Chang, S. G. Hwang, and I. S. Choe.
2005
. Effects of wood vinegar addition for meat quality improvement of old layer.
Kor. J. Poult. Sci.
 
32
:
101
–106.
15
Kirchgessner
,
M.
, and F. X. Roth.
1982
. Fumaric acid as a feed additive in pig nutrition.
Pig News Inf.
 
3
:
259
–264.
16
Lactacid (composite of Ca-formate 17%, Ca-propionate 5%, Ca-lactate 15%, citric acid 27%, and carrier 36%), Eunjin Bio Co., Cheonan-si, Korea.
17
Phytase-5000, 5000 μg/g (phytase/powder), Fujian Fuda Biotech Co., Fuzhou City, Fujian, P. R. China.
18
Hy-Line Brown, Hy-Line International, InJoo Co., Pyeongtaek-si, Korea.
19
Texture analyzer, Stable Micro System Ltd., Vienna Court, Surrey, UK.
20
Model 7360 Dial Pipe Gauge, Mitutoyo Co., Kawasaki, Japan.
21
Eisen
,
E. J.
, B. B. Bohren, and H. E. McKean.
1962
. The Haugh unit as a measure of egg albumen quality.
Poult. Sci.
 
41
:
1461
–1468.
22
Haugh unit measuring instrument, Ames, Waltham, MA.
23
Eggshell color, Samyang Co., Seoul, Korea; egg yolk color, Roche Co., Basel, Switzerland.
24
Hatta
,
H.
, J. S. Sim, and S. Nakai.
1988
. Separation of phospholipids from egg yolk and recovery of water-soluble proteins.
J. Food Sci.
 
53
:
425
–427.
25
Hatta
,
H.
, M. Kim, and T. Yamamoto.
1990
. Novel isolation method for hen egg yolk antibody, “IgY.”
Agric. Biol. Chem.
 
54
:
2531
–2535.
26
Chicken IgY enzyme-linked immunosorbent assay (ELISA) kit, catalog no. 6030, Alpha Diagnostics International Inc., San Antonio, TX.
27
SAS Institute.
1996
. SAS User’s Guide: Statistics. Version 6.11. SAS Inst. Inc., Cary, NC.
28
Boling-Frankenbach
,
S. D.
, J. L. Snow, C. M. Parsons, and D. H. Baker.
2001
. The effects of citric acid on the calcium and phosphorus requirements of chicks fed corn-soybean meal diets.
Poult. Sci.
 
80
:
783
–788.
29
Sohil
,
S. S.
, and D. A. Roland.
2002
. Influence of dietary phosphorus on performance of Hy-Line W36 hens.
Poult. Sci.
 
81
:
75
–83.
30
Dhawale
,
A.
2005
. Better eggshell quality with a gut acidifier.
Poult. Int.
 
44
:
18
–20.
31
Soltan
,
M. A.
2008
. Effect of dietary organic acid supplementation on egg production, egg quality and some blood serum parameters in laying hens.
Int. Poult. Sci.
 
7
:
613
–621.
32
Son
,
J. H.
, D. Ragl, and O. Adeola.
2002
. Quantification of digestive flow into the caeca.
Br. Poult. Sci.
 
43
:
322
–324.
33
Izat
,
A. L.
, M. H. Adams, M. C. Cabel, M. Colberg, M. A. Reiber, J. T. Skinner, and P. W. Waldroup.
1990
. Effect of formic acid or calcium formate in feed on performance and microbiological characteristics of broiler.
Poult. Sci.
 
69
:
1876
–1882.
34
Woo
,
K. C.
, M. K. Lee, B. Y. Jung, and I. K. Paik.
2006
. Effect of acidifier (Lactacid) and essential oil (Immunocin) on the performance, nutrient metabolizability, small intestinal microflora and immune response in broiler chicks.
Kor. J. Poult. Sci.
 
33
:
141
–149.
35
Park
,
J. H.
, G. H. Park, and K. S. Ryu.
2002
. Effect of feeding organic acid mixture and yeast culture on performance and egg quality of laying hens.
Kor. J. Poult. Sci.
 
29
:
109
–115.
36
Kemme
,
P. A.
, J. T. M. Diepen, and A. W. Jongbloed.
1998
. The relationship between graded doses of Lupro-Cid and the apparent total tract, digestibility of total phosphorus and calcium in growing pigs. Rep. ID-DLO No. 98012. Inst. Anim. Sci. Health, Lelystad, the Netherlands.
37
Kirchgessner
,
M.
, B. Gedek, S. Wiehler, A. Bott, U. Eidelsburger, and F. X. Roth.
1992
. Influence of formic acid, calcium formate and sodium hydrogen carbonate on the microflora in different segments of the gastrointestinal tract. 10. Communication. Investigations about the nutritive efficacy of organic acids in the rearing of piglets.
J. Anim. Physiol. Anim. Nutr. (Berl.)
 
68
:
73
–81.
38
Eidelsburger
,
U.
, M. Kirchgessner, and F. X. Roth.
1992
. Influence of fumaric acid, hydrochloric-acid, sodium formate, tylosin and toyocerin on daily weight gain, feed intake, feed conversion rate and digestibility. 11. Investigations about the nutritive efficacy of organic acids in the rearing of piglets.
J. Anim. Physiol. Anim. Nutr. (Berl.)
 
68
:
82
–92.
39
Defa
,
L.
, S. D. Liu, S. Y. Qiao, G. F. Yi, C. Liang, and P. Thacker.
1999
. Effect of feeding organic acid with or without enzyme on intestinal microflora, intestinal enzyme activity and performance of weaned pigs.
Asian-Aust. J. Anim. Sci.
 
12
:
411
–416.
40
Al-Tarazi
,
Y. H
, and K. Alshawabkeh.
2003
. Effect of dietary formic and propionic acid mixture on limiting Salmonella pullorum in layer chicks.
Asian-Aust. J. Anim. Sci.
 
16
:
77
–82.
41
Solomon
,
S. E.
1997
. Egg and Eggshell Quality. Iowa State University Press, Ames.
42
Partanen
,
K. H.
, and Z. Mroz.
1999
. Organic acid for performance enhancement in pig diets.
Nutr. Res. Rev.
 
12
:
117
–145.