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INTRODUCTION
Palm kernel meal (PKM) is a by-product of palm kernel during palm oil extraction, which is mostly produced in Southeast Asia countries (e.g., Indonesia and Malaysia). Because of its nutritional values and low production cost, PKM has been considered an economical ingredient for poultry diets [1]. It has been reported that inclusion of PKM up to 40% in poultry diets has no adverse effects on productive performance [2,3]. However, poultry nutritionists often hesitate to use the large amounts of PKM in diets because of its adverse properties such as dark color and poor essential amino acid profiles. In addition, PKM contains the relatively high amounts of nonstarch polysaccharides (NSP), which is well-known as an antinutritional factor due to impairment in nutrient digestion and absorption in the gastrointestinal tract of animals [4,5]. Therefore, dietary supplementation of NSP-degrading enzymes (NSPase) is widely used in the feed industry when PKM is included in the diet. In particular, dietary β-mannanase is often supplemented to diets containing PKM because β-mannan is the major NSP in PKM [6]. It has been reported that dietary supplementation of β-mannanase in diets containing PKM improved productive performance of broiler chickens and laying hens [7,8]. Dietary β-xylanase may also be considered a potential NSPase in diets containing PKM because xylan is also present at the high amount in PKM [6]. Supplementation of β-xylanase in diets containing PKM was reported to improve growth performance of broiler chickens [9]. However, there is currently little information regarding the interactive effects of dietary PKM and β-xylanase supplementation in laying hens.
Therefore, the objectives of the present experiment were to investigate the effects of dietary PKM and β-xylanase supplementation on productive performance, egg quality, fatty liver incidence, and excreta characteristics in laying hens.
MATERIALS AND METHODS
The protocol for the current experiment was reviewed and approved by the Institutional Animal Care and Use Committee at Chung-Ang University (IACUC No. 2020-00042). A total of 320 Hy-Line Brown laying hens (Icheon, Korea) with 33 weeks of age were allotted to 1 of 4 dietary treatments with 8 replicates in a feeding trial. Each replicate consisted of 10 consecutive cages with 1 hen per cage (37 cm × 30 cm × 40 cm = width × length × height). The experiment was conducted in a completely randomized design with a 2 × 2 factorial arrangement with dietary supplementation of PKM and β-xylanase. The control diet was formulated mainly with corn and soybean meal. Additional diet was prepared with the inclusion of 10% PKM in the control diet with a partial replacement of corn and soybean meal. The commercial PKM was used in this experiment and nutritional compositions of PKM is presented in Table 1. In addition, 0.025% β-xylanase (Econase®XT, declared activity of 4,000,000 unit/g, AB Vista, Marlborough, UK) was supplemented to 2 of 4 treatment diets by replacing the same amounts of celite in treatment diets. All nutrients and energy in the experimental diets were formulated to meet or exceed recommendations of the Hy-Line International [10] (Table 2). The diets and water were provided ad libitum for 8 weeks. The cages were placed in an environmentally-controlled laying house with 16 h of lighting and 8 h of darkness. Temperature and humidity were maintained at 23 ± 3 °C and 64 ± 9% throughout the entire experiment, respectively.
1) Adopted from Heuzé et al. with CC-BY-NC [17].
1) Provided per kg of the complete diet: vitamin A, 10,000 IU (retinyl acetate); vitamin D3, 4,500 IU; vitamin K3, 3.0 mg (menadione dimethpyrimidinol); vitamin B1, 2.50 mg; vitamin B2, 6.50 mg; vitamin B6, 3.20 mg; vitamin B12, 18.0 µg; biotin, 180 µg; folic acid, 1.9 mg; niacin, 60 mg.
2) Provided per kg of the complete diet: cobalt, 1,200 µg (CoSO4); copper, 19.0 mg (CuSO4); iron, 72 mg (FeSO4); iodine, 1.5 mg (Ca[IO3]2); manganese, 144.0 mg (MnO); selenium, 360 µg (Na2SeO3); zinc, 120 mg (ZnSO4).
The color of diets was measured using a colorimeter (model CR-10, Konica Minolta Optics, Tokyo, Japan) to assess the color change due to the inclusion of 10% PKM.
Hen-day egg production, egg weight (EW), and broken and shell-less egg production rate were recorded daily. Feed intake (FI) and feed conversion ratio (FCR) were recorded at 4-week intervals. Egg mass (EM) was calculated based on hen-day egg production and EW. The data for productive performance were summarized for 8 weeks of the feeding trial.
Egg quality was analyzed with 12 eggs per replicate, which were randomly collected at the end of the experiment. Eggshell color was determined by the method described by Kim et al. [11]. In short, eggshell color was determined using the eggshell color fan (Samyangsa, Wonju, Korea) with different scales from 1 to 15 (1 = light white; 15 = dark brown). The CIE color scale for L*, a*, and b* were also measured using a colorimeter (model CR-10, Konica Minolta Optics). Egg yolk color, haugh unit, and eggshell strength were analyzed using digital egg tester (DET-6000, Nabel, Tokyo, Japan) as reported previously [12].
At the end of experiment, the individual body weight (BW) of all laying hens was recorded. One hen with the closest average BW per replicate was chosen and euthanized by CO2 asphyxiation. For a measure of fatty liver incidence, images of the liver attached on the body were pictured to determine the subjective fatty liver score on a scale from 1 to 5 (1 = dark red; 5 = yellowish red) [13]. In addition, the objective CIE color scale for the L*, a*, and b* were also determined using a colorimeter (model CR-10, Konica Minolta Optics). Afterward, the liver was detached, weighed, and collected for measuring total lipid concentrations [14].
At the end of the feeding trial (41 weeks of age), 24 laying hens (i.e., 6 hens per treatment) were selected and randomly placed in metabolic cages with one bird per cage (35.2 cm × 45.0 cm × 55.3 cm = width × length × height) to measure excreta characteristics based on the method described by Ogunji et al. [15] (Table 6). The excreta moisture score was visually measured on a scale from 1 to 4 (1 = normal dry droppings and coning; 2 = slightly loose droppings, some coning but no free water; 3 = loose droppings with slight coning and some free water; 4 = extremely loose droppings with no coning and large amounts of free water). Excreta samples were also collected daily from each cage to analyze the actual moisture concentrations. Excreta moisture concentrations were determined using drying oven at 100°C for 12 h [16].
The samples for PKM and experimental diets were dried and finely ground for analyzing the concentrations of crude protein (CP; method 990.03), dry matter (DM; method 930.15), crude ash (method 942.05), ether extract (method 2003.05), neutral detergent fiber (method 2002.04), and acid detergent fiber (method 973.18) as followed by the AOAC methods [14]. In addition, the concentrations of amino acids in PKM were analyzed by the AOAC (method 982.30) [14]. The concentrations of gross energy in the samples were analyzed using a bomb calorimetry (Model 6400; Parr Instruments, Moline, IL, USA) with benzoic acid used as the calibration standard [14].
All data were analyzed by 2-way ANOVA (analysis of variance) in a completely randomized design with the GLM procedure of SAS (SAS Institute, Cary, NC, USA). The replicate was used as an experimental unit. Outliers were checked using the UNIVARIATE procedure of SAS. The model included the effects of dietary PKM, β-xylanase supplementation, and their interaction as fixed variables. However, there were no significant interactions for all measurements. The MEANS procedure was used to calculate treatment means. Significance for statistical test was set at p < 0.05.
RESULTS AND DISCUSSION
The concentrations of CP in PKM (13.4%) were slightly less than previously reported values (15.2%) [17], which may be the reason why analyzed CP concentrations in diets were decreased with 10% inclusion levels of PKM (Table 2), although treatment diets were formulated to maintain equivalent CP concentrations among treatment diets. However, the concentrations of other nutrients in PKM were similar to those values reported previously [17]. Therefore, the PKM used in the current experiment can be considered the typical and representative PKM used in the commercial animal diet. Moreover, the color of diets containing 10% PKM was darker (i.e., 14.8% less lightness) than the color of diets containing no PKM, which is likely due to the dark color of PKM.
No significant interactions for all measurements were observed between dietary PKM and β-xylanase supplementation. This result was unexpected because inclusion of PKM in diets increases the amounts of viscous NSP, which is known to be detrimental on layer production; therefore, dietary β-xylanase supplementation would alleviate the negative effects. The possible reason may be that the amount of xylan in PKM is relatively low enough to exert significant effect of dietary β-xylanase [6]. Aderibigbe et al. [18] also reported no positive effects of dietary supplementation of β-xylanase in diets containing PKM on growth performance of broiler chickens. In addition, the current inclusion levels of PKM (i.e., 10%) is insufficient to induce a significant antinutritional effect.
Inclusion of 10% PKM in layer diets did not affect productive performance, except that hens fed diets containing 10% PKM had greater (p < 0.05) FI than those fed diets containing no PKM (Table 3). Likewise, dietary supplementation of 0.025% β-xylanase had no effects on productive performance of laying hens. This result agreed with previous experiments reporting no significant effects of inclusion of 10% PKM in diets on productive performance of laying hens [1,2]. However, increased FI was observed by feeding diets containing 10% PKM to laying hens in this experiment. The reason for this observation may be related to high amounts of fiber in PKM. Poultry has a tendency to consume diets until the energy and nutrient requirements are satisfied [19]. Dietary fiber is an antinutritional factor that is associated with decreased available energy and nutrients in diets, and therefore, increases in dietary fiber are often related to increased FI, which is required to compensate for the decreased intake of available energy and nutrients [4,20]. No differences in other productive performance such as hen-day egg production, EW, EM, and FCR also supported that hens fed diets containing 10% PKM had available energy and nutrient that are similar to those fed diets containing no PKM. Dietary β-xylanase supplementation has been reported to ameliorate antinutritional effects of NSP such as xylan in PKM [4]. However, all measurements for productive performance were not influenced by dietary β-xylanase supplementation in the current experiment. This observation may be explained by the fact that antinutritional effects of xylan are not noticeable when 10% PKM is included in diets. Perez et al. [2] and Abdollahi [7] also reported that 10% PKM in the diet had no antinutritional effects on productive performance of laying hens.
There were no differences in all egg quality measurements, except for egg yolk color, by feeding diets containing 10% PKM to laying hens (Table 4). For egg yolk color, hens fed diets containing 10% PKM had greater (p < 0.05) yolk color than those fed diets containing no PKM. This result agreed with previous experiments reporting that feeding diets containing PKM or fermented PKM to laying hens increased egg yolk color score [21,22]. The reason is likely that PKM contains high amounts of carotenoids, which are the main chemical compounds responsible for the yellow coloration of egg yolk [22,23]. However, egg quality was not affected by dietary β-xylanase supplementation, regardless of inclusion of 10% PKM in diets [1].
1) Eggshell color was measured by the color fan scale and CIE [11].
Neither inclusion of 10% PKM or 0.025% β-xylanase supplementation in diets influenced visual inspection scores of fatty liver, CIE colors, and lipid concentrations in the liver (Table 5). Fatty liver syndrome (FLS) or fatty live hemorrhagic syndrome (FLHS) frequently occurs in laying hens, which is often associated with considerable economical losses in layer production [24]. In particular, FLS or FLHS prevails for laying hens that are raised in confined cages. The primary etiology includes dietary nutrients, environment, hormones, and genetic factors [13,25]. It has been reported that feeding high amounts of dietary fiber to laying hens may decrease the progress of fatty liver development by regulating lipid transport from or to the liver [26]. In addition, Akiba and Matsumoto [27] reported that dietary fiber increases lipoproetin lipase activity and reduces hormone-sensitive lipase activity, which was suggested as the reason for decreased liver lipid deposition in chicks. This is the reason why we hypothesized that inclusion of 10% PKM in diets may decrease the characteristics of fatty liver development; however, no such beneficial effect was observed in this experiment. This lack of response may be due to the fact that animals (e.g., age of hens) and environment (e.g., dietary compositions and stocking density) in the current experiments may not be enough to increase susceptibility to fatty liver development in laying hens.
Visual excreta scores and moisture concentrations were not affected by inclusion of 10% PKM in diets (Table 6). In addition, dietary β-xylanase supplementation did not influence on the excreta scores and moisture concentrations, regardless of PKM in diets. Watery excreta is highly associated with increasing production of dirty eggs, which are easily contaminated by microbes, jeopardizing the egg safety [28]. Jimenez-Moreno et al. [29] reported that excreta moisture concentrations were positively correlated with fiber concentrations in poultry diets. However, although inclusion of 10% PKM increased fiber concentrations in diets, excreta score and moisture concentrations were not influenced by inclusion of 10.0% PKM in diets. It has been reported that viscous excreta induced by soluble NSP may also increase excreta moisture concentrations [30]. Thus, we expected that dietary β-xylanase supplementation may ameliorate excreta moisture concentrations when PKM is included in diets, but we failed to find the interactive effect. No change in excreta score and moisture concentrations by feeding diets containing 10% PKM appears to explain why dietary β-xylanase supplementation had no effects on excreta score and moisture concentrations.
1) Excreta moisture score was measured by the scale [15].
In conclusion, PKM can be a potential feed ingredient for laying hens at the inclusion of 10% in the diet. It appears that dietary β-xylanase used in the current experiment has little effect on layer productivity, regardless of inclusion of 10% PKM in the diet. Inclusion of 10% PKM in diets is effective in improving egg yolk color of laying hens. In addition, inclusion of 10% PKM in layer diets does not increase the dirty egg production by increasing watery excreta production.
