Abstract
This study evaluated the effects of 1,3-diacylglycerol (DAG) supplementation on the growth performance, nutrient digestibility, and physiological responses of broilers fed reduced-energy diets containing palm kernel meal (PKM). A total of 576 one-day-old mixed-sex Ross 308 broiler chicks were randomly allocated to four dietary treatments: positive control (PC), negative control (NC; PC − 100 kcal/kg ME and 5% PKM), T1 (NC + 0.05% 1,3-DAG), or T2 (NC + 0.10% 1,3-DAG). Broilers were fed the experimental diets for 35 d, and apparent total tract digestibility was determined during d 28–35 using chromium oxide as an indigestible marker. During the overall period (d 1–35), body weight gain and feed intake were not affected by dietary treatment (P > 0.05), whereas the feed conversion ratio (FCR) was significantly higher in the NC group than in the PC group (P < 0.001). Dietary 1,3-DAG supplementation linearly improved FCR (P < 0.001), and the FCR of the T2 group was comparable to that of the PC group. The apparent total tract digestibility of DM, nitrogen, energy, and fat was not affected by treatment (P > 0.05); however, significant linear increases in DM (P = 0.049), energy (P = 0.015), and fat digestibility (P < 0.001) were observed with increasing 1,3-DAG supplementation. Nutrient intake and retention were largely unaffected by treatment (P > 0.05), although fat intake was significantly higher in the NC group than in the PC group (P = 0.012). In contrast, nutrient excretion, particularly fat excretion, was significantly reduced by 1,3-DAG supplementation in a dose-dependent manner (P < 0.001). Serum lipid profiles and rectal temperature were not influenced by dietary treatment (P > 0.05). In conclusion, dietary 1,3-DAG supplementation improved FCR in broilers fed PKM-based reduced-energy diets by enhancing nutrient utilization, particularly fat digestibility, without affecting their physiological parameters.
Keywords: Emulsifier, Palm kernel meal, Broiler, Feed efficiency, Fat digestibility
Introduction
The increasing demand for cost-effective and sustainable feed ingredients has led to the growing use of agro-industrial by-products, such as palm kernel meal (PKM), in poultry diets. Palm kernel meal is widely utilized because of its availability and relatively low cost; however, its use in broiler diets is limited by its high fiber content and relatively low energy value (Azizi et al., 2021; Panigrahi and Powell, 1991). In particular, the presence of non-starch polysaccharides and the encapsulation of nutrients, including lipids, within fibrous cell wall structures can limit the accessibility of nutrients to digestive enzymes, thereby reducing nutrient digestibility (Alshelmani et al., 2016). Previous studies have reported that high inclusion levels of PKM may impair feed efficiency and growth performance, thereby limiting its application in high-performance broiler production systems (Azizi et al., 2021; Panigrahi and Powell, 1991). These negative effects are often exacerbated when dietary energy is reduced, as broilers are highly sensitive to energy density for optimal growth and feed conversion efficiency.
To overcome these limitations, dietary supplementation with emulsifiers has been proposed as a nutritional strategy to enhance lipid digestion and improve energy utilization. Emulsifiers facilitate micelle formation, thereby increasing the accessibility of lipids to digestive enzymes, such as lipases, and improving fat absorption in the small intestine (McClements and Jafari, 2018; Upadhaya et al., 2019). Among the various emulsifiers, 1,3-diacylglycerol (DAG) has attracted attention because of its potential to enhance lipid digestion and utilization in poultry (Liu et al., 2020; Upadhaya et al., 2017). Unlike conventional emulsifiers such as lecithin or lysophospholipids, which primarily enhance fat emulsification through their amphiphilic properties, DAG is a glyceride-based emulsifier that facilitates micelle formation and may further enhance lipid digestion and absorption because of its glyceride structure and dual functionality (McClements and Jafari, 2018; Upadhaya et al., 2019). These characteristics may improve lipid digestion and energy utilization, particularly in reduced-energy diets (Liu et al., 2020; Upadhaya et al., 2017).
Palm kernel meal typically contains approximately 7–10% residual oil together with relatively high concentrations of crude fiber (13–18%) and non-starch polysaccharides (NSP), characteristics that can reduce nutrient digestibility and energy utilization in broilers (Alimon, 2004; Azizi et al., 2021; Sharmila et al., 2014). Although PKM contains residual oil, this lipid fraction may not be efficiently utilized because of the fibrous matrix surrounding the nutrients. Therefore, dietary emulsifiers may represent a promising nutritional strategy to improve the utilization of PKM-based reduced-energy diets. Despite these advantages, limited information is available regarding the efficacy of emulsifier supplementation in reduced-energy diets containing PKM, particularly under practical feeding conditions. In addition, rectal temperature was included as a physiological indicator to determine whether improved energy utilization associated with dietary 1,3-DAG supplementation influences the thermoregulatory status of broilers.
We hypothesized that dietary supplementation with 1,3-DAG would improve fat utilization and feed efficiency in broilers fed PKM-based reduced-energy diets without adversely affecting systemic lipid metabolism or thermoregulatory status. Therefore, the present study was conducted to evaluate the effects of dietary 1,3-DAG supplementation on growth performance, nutrient digestibility, fat utilization, serum lipid profiles, and rectal temperature in broilers.
Materials and methods
All experimental procedures involving animals were reviewed and approved by the Institutional Animal Care and Use Committee of Dankook University, Korea (Approval No. DK-1-2502).
Experimental design and diets
A total of 576 one-day-old mixed-sex Ross 308 broiler chicks were randomly allotted to one of four dietary treatments: positive control (PC), negative control (NC; PC − 100 kcal/kg ME and 5% PKM), T1 (NC + 0.05% 1,3-DAG), or T2 (NC + 0.10% 1,3-DAG), with eight replicate cages per treatment and 18 birds per cage. Birds were housed in multi-tier battery cages equipped with feeders and nipple drinkers and were allowed ad libitum access to feed and water. Environmental conditions were maintained according to standard commercial broiler management guidelines, with room temperature gradually reduced from 32 to 34°C at placement to approximately 22–24°C by the end of the experiment, and relative humidity maintained at 60–70%. A continuous lighting program was applied during the first 3 days, followed by a 23L:1D lighting schedule thereafter.
The PC treatment consisted of corn–soybean meal-based diets formulated to meet NRC (1994) and NIAS (2022) requirements (Table 1). Experimental diets were provided in three feeding phases: starter (d 1–9), grower (d 10–20), and finisher (d 21–35). The dietary crude protein (CP) and ME levels of the PC diets were set at 23% and 3,200 kcal/kg for the starter phase, 21.5% and 3,200 kcal/kg for the grower phase, and 20% and 3,200 kcal/kg for the finisher phase (Table 1).
Table 1.
Ingredient and nutrient composition of the experimental diets.
| Item | Starter (d 1–9) |
Grower (d 10–20) |
Finisher (d 21–35) |
|||
|---|---|---|---|---|---|---|
| PC (Basal diet) | NC (−100 kcal/kg) |
PC (Basal diet) | NC (−100 kcal/kg) |
PC (Basal diet) | NC (−100 kcal/kg) |
|
| Ingredients (%) | ||||||
| Corn | 43.95 | 39.98 | 48.79 | 44.81 | 55.84 | 51.88 |
| Soybean meal (48%) | 34.83 | 33.55 | 31.00 | 29.71 | 27.77 | 26.48 |
| Corn gluten meal | 13.00 | 13.00 | 13.00 | 13.00 | 10.00 | 10.00 |
| Palm kernel meal | - | 5.00 | - | 5.00 | - | 5.00 |
| Wheat bran | 3.00 | 3.00 | 3.00 | 3.00 | 3.00 | 3.00 |
| Soy oil | 1.59 | 1.85 | 1.32 | 1.57 | 0.85 | 1.10 |
| MDCP | 1.66 | 1.66 | 1.30 | 1.30 | 1.01 | 1.01 |
| Limestone | 1.09 | 1.06 | 0.79 | 0.79 | 0.73 | 0.72 |
| Salt | 0.36 | 0.36 | 0.36 | 0.36 | 0.36 | 0.36 |
| Methionine (99%) | 0.20 | 0.20 | 0.17 | 0.17 | 0.17 | 0.16 |
| Lysine (78%) | 0.12 | 0.14 | 0.07 | 0.09 | 0.07 | 0.09 |
| Mineral mix1 | 0.10 | 0.10 | 0.10 | 0.10 | 0.10 | 0.10 |
| Vitamin mix2 | 0.10 | 0.10 | 0.10 | 0.10 | 0.10 | 0.10 |
| Total | 100.00 | 100.00 | 100.00 | 100.00 | 100.00 | 100.00 |
| Calculated value | ||||||
| Crude protein, % | 23.00 | 23.00 | 21.50 | 21.50 | 20.00 | 20.00 |
| ME, kcal/kg | 3,200 | 3,100 | 3,200 | 3,100 | 3,200 | 3,100 |
| Ca, % | 0.95 | 0.95 | 0.75 | 0.75 | 0.65 | 0.65 |
| P, % | 0.79 | 0.80 | 0.71 | 0.72 | 0.63 | 0.64 |
| Available P, % | 0.50 | 0.50 | 0.42 | 0.42 | 0.36 | 0.36 |
| Total Lys, % | 1.32 | 1.32 | 1.18 | 1.18 | 1.08 | 1.08 |
| Total Met, % | 0.55 | 0.55 | 0.51 | 0.51 | 0.48 | 0.48 |
| Crude fat, % | 4.29 | 4.78 | 4.13 | 4.61 | 3.73 | 4.21 |
| Fiber, % | 3.54 | 4.44 | 3.50 | 4.40 | 3.33 | 4.22 |
| Ash, % | 6.77 | 6.85 | 5.92 | 6.02 | 5.30 | 5.40 |
PC, positive control diet; NC, negative control diet with 100 kcal/kg reduced ME; T1, NC supplemented with 0.05% 1,3-diacylglycerol (1,3-DAG); T2, NC supplemented with 0.10% 1,3-DAG.
Provided per kg of complete diet: 37.5 mg Zn (as ZnSO4); 37.5 mg Mn (as MnO2); 37.5 mg Fe (as FeSO4·7H2O); 3.75 mg Cu (as CuSO4·5H2O); 0.83 mg I (as KI); and 0.23 mg Se (as Na2SeO3·5H2O).
Provided per kg of complete diet:15,000 IU of vitamin A, 3,750 IU of vitamin D3, 37.5 IU of vitamin E, 2.55 mg of vitamin K3, 3 mg of Thiamin, 7.5 mg of Rivoflavin, 4.5 mg of vitamin B6, 24 ug of vitamin B12, 51 mg of Niacin, 1.5 mg of Folic acid, 0.2 mg of Biotin and 13.5 mg of Ca-Pantothenate.
To formulate the NC diet, corn was partially replaced with 5% PKM, and dietary ME was reduced by 100 kcal/kg through adjustments in corn, soybean meal, and soybean oil across all feeding phases. Previous studies have demonstrated that PKM can be included in broiler diets at levels of up to 10–15% without adversely affecting growth performance when appropriately processed or supplemented (Azizi et al., 2021). However, an inclusion level of 5% PKM was selected in the present study to establish a practical reduced-energy dietary model while minimizing potential confounding effects associated with higher PKM inclusion levels, thereby allowing a clearer evaluation of the effects of dietary 1,3-DAG supplementation.
The nutrient composition of the PKM used in this study was as follows: DM, 90.6%; ME, 1,040 kcal/kg; CP, 18.3%; crude fiber, 20.7%; ash, 4.8%; crude fat, 7.8%; calcium, 0.30%; and total phosphorus, 0.61%. The 1,3-DAG product (Il Shin Wells, Seoul, Korea) contained 55% 1,3-DAG isomer in a 70:30 medium- and long-chain triglyceride carrier. Its fatty acid composition was 50% lauric acid, 20% capric acid, and 30% myristic plus palmitic acids, and its lipid composition was 20% monoacylglycerol, 60% 1,3-DAG, and 20% triacylglycerol.
Growth performance
Individual body weight (BW) was measured at the end of each feeding phase (d 9, 20, and 35) to calculate body weight gain (BWG). Feed intake (FI) was calculated as the difference between the amount of feed offered and the feed remaining in the feeders. Feed conversion ratio (FCR) was calculated as FI/BWG and adjusted for mortality by accounting for the body weight of dead birds.
Nutrient digestibility
To determine apparent total tract digestibility (ATTD), chromium oxide (Cr₂O₃) was added at 0.2% to the experimental diets during the finisher phase (d 28–35) as an indigestible marker. On d 35, fresh excreta samples were collected repeatedly from each cage using collection trays to minimize contamination with feathers and feed residues. Excreta samples collected from the same cage were immediately stored at −20°C until analysis. Before chemical analysis, the frozen samples were thawed, pooled by cage, dried in a forced-air oven at 105°C for 24 h, and ground to pass through a 1-mm screen to ensure homogeneity. Diet and excreta samples were analyzed in duplicate for DM (AOAC method 934.01), nitrogen (AOAC method 984.13), and ether extract (AOAC method 920.39) according to AOAC (2001). Nitrogen content was determined by the Kjeldahl method, and crude protein was calculated as nitrogen × 6.25. Gross energy was measured using an adiabatic oxygen bomb calorimeter (Parr 6400; Parr Instrument Co., Moline, IL, USA). Chromium concentrations in diet and excreta samples were determined using a UV-visible spectrophotometer (UV-1201; Shimadzu, Kyoto, Japan) following wet-ash digestion.
Apparent total tract digestibility was calculated using the following equation:
ATTD (%) = 100 × [1 − (Nf × Crd) / (Nd × Crf)] where Nf and Nd represent the nutrient concentrations (%) in feces and diet, respectively, and Crd and Crf represent the chromium concentrations (%) in feces and diet, respectively.
Nutrient retention and excretion
Nutrient retention and excretion were estimated on the basis of FI and ATTD values obtained in the present study. Feed intake during the digestibility measurement period (d 28–35) was recorded on a cage basis and used to calculate nutrient intake. The ATTD values measured on d 35 were then used to estimate the retention and excretion of DM, nitrogen, energy, and fat.
Nutrient intake (g/d) was calculated as follows: feed intake (g/d) × nutrient concentration in the diet (%)
Nutrient retention (g/d) was calculated as follows: nutrient intake × ATTD (%)
Nutrient excretion (g/d) was calculated as follows: nutrient intake − nutrient retention
Serum lipid profiles
On d 35, blood samples were collected from the wing vein into EDTA tubes, centrifuged at 3,000 × g for 15 min at 4°C, and the separated serum samples were stored at −20°C until analysis. Serum concentrations of triglyceride, total cholesterol, HDL-cholesterol, and LDL-cholesterol were determined using an automatic clinical chemistry analyzer (Hitachi 7020, Hitachi High-Technologies, Tokyo, Japan) with enzymatic kits.
Rectal temperature measurement
Rectal temperature was measured on d 35 using a digital thermometer (Testo 925; Testo SE & Co., Germany). The probe was gently inserted approximately 2–3 cm into the cloaca until a stable reading was obtained.
Statistical analysis
Data were analyzed using one-way analysis of variance (ANOVA) with dietary treatment as the main effect. When a significant treatment effect was detected, means were separated using Tukey’s multiple comparison test. Orthogonal contrasts were performed to compare the PC and NC treatments, and to evaluate the linear and quadratic effects of dietary 1,3-DAG supplementation (0, 0.05, and 0.10%) among NC, T1, and T2, excluding the PC group. For growth performance parameters, the cage was considered the experimental unit. For serum lipid profiles and rectal temperature, individual birds (n = 16 per treatment) were used as the experimental unit. Results were expressed as means with standard error of the mean (SEM). Statistical significance was declared at P < 0.05.
Results
Growth performance
Growth performance results are presented in Table 2. During the starter phase (days 1–9), no significant differences were observed among treatments in BWG, FI, or FCR (P > 0.05). During the grower phase (days 10–20), BWG increased linearly with increasing levels of 1,3-DAG supplementation (P = 0.015), although the overall treatment effect was not significant (P = 0.095). Feed intake was not affected by dietary treatment (P > 0.05). However, FCR was significantly affected by dietary treatment (P < 0.001), with the NC group showing a higher FCR than the PC group (P = 0.006). In addition, a significant linear improvement in FCR was observed with increasing levels of 1,3-DAG supplementation (P < 0.001), whereas no significant quadratic response was detected. During the finisher phase (days 21–35), BWG increased linearly with 1,3-DAG supplementation (P = 0.013), although the overall treatment effect was not significant (P = 0.064). Feed intake was not affected by dietary treatment (P > 0.05). FCR was significantly affected by dietary treatment (P < 0.001), with the NC group exhibiting the highest FCR. Both T1 and T2 groups showed improved FCR compared with NC, and a significant linear response to increasing dietary 1,3-DAG supplementation was observed (P < 0.001), whereas no significant quadratic response was detected. Over the entire experimental period (d 1–35), final BW and BWG were not significantly affected by dietary treatment (P > 0.05), although both variables increased linearly with increasing dietary 1,3-DAG levels (P = 0.020), with no significant quadratic response. Feed intake was not affected by dietary treatment (P > 0.05). In contrast, FCR was significantly affected by dietary treatment (P < 0.001), with the NC group showing the highest value. 1,3-DAG supplementation improved FCR in a dose-dependent manner, showing a significant linear response (P < 0.001) with no significant quadratic response. Furthermore, the T2 group exhibited an FCR comparable to that of the PC group.
Table 2.
Effects of dietary 1,3-diacylglycerol supplementation on growth performance in broiler chickens.
| Treatment |
PC vs NC | Linear | Quadratic | ||||||
|---|---|---|---|---|---|---|---|---|---|
| PC | NC | T1 | T2 | SEM | P-value | P-value | P-value | P-value | |
| d 1 to 9 | |||||||||
| BWG, g | 202 | 198 | 201 | 203 | 4.48 | 0.878 | 0.574 | 0.460 | 0.947 |
| FI, g | 223 | 224 | 222 | 225 | 4.67 | 0.974 | 0.817 | 0.888 | 0.699 |
| FCR | 1.101 | 1.134 | 1.106 | 1.109 | 0.012 | 0.207 | 0.098 | 0.156 | 0.314 |
| d 10 to 20 | |||||||||
| BWG, g | 698 | 672 | 684 | 714 | 11.86 | 0.095 | 0.152 | 0.015 | 0.535 |
| FI, g | 853 | 872 | 859 | 866 | 13.88 | 0.773 | 0.178 | 0.791 | 0.584 |
| FCR | 1.224b | 1.300a | 1.256ab | 1.213b | 0.014 | <0.001 | 0.006 | <0.001 | 0.956 |
| d 21 to 35 | |||||||||
| BWG, g | 997 | 936 | 972 | 1015 | 20.86 | 0.064 | 0.081 | 0.013 | 0.884 |
| FI, g | 1,579 | 1,628 | 1,589 | 1,597 | 39.47 | 0.834 | 0.419 | 0.497 | 0.570 |
| FCR | 1.581b | 1.745a | 1.636b | 1.572b | 0.02 | <0.001 | <0.001 | <0.001 | 0.328 |
| d 1 to 35 | |||||||||
| BW, g | 1,945 | 1,853 | 1,904 | 1,979 | 35.84 | 0.109 | 0.122 | 0.020 | 0.783 |
| BWG, g | 1,897 | 1,805 | 1,856 | 1,931 | 35.87 | 0.109 | 0.122 | 0.020 | 0.784 |
| FI, g | 2,654 | 2,724 | 2,670 | 2,688 | 51.35 | 0.826 | 0.363 | 0.614 | 0.571 |
| FCR | 1.399c | 1.511a | 1.438b | 1.391c | 0.012 | <0.001 | <0.001 | <0.001 | 0.397 |
PC, positive control diet; NC, negative control diet with 100 kcal/kg reduced ME; T1, NC supplemented with 0.05% 1,3-diacylglycerol (DAG); T2, NC supplemented with 0.10% 1,3-DAG. SEM, standard error of the mean.
BWG, body weight gain; FI, feed intake; FCR, feed conversion ratio.
Means within a row with different superscripts differ significantly at P < 0.05. Orthogonal contrasts were used to determine the linear and quadratic effects of dietary 1,3-DAG supplementation (0, 0.05, and 0.10%) among NC, T1, and T2.
Nutrient digestibility
The effects of dietary 1,3-DAG supplementation on nutrient digestibility are presented in Table 3. No significant differences were observed among treatments in the ATTD of DM, nitrogen, energy, or fat (P > 0.05). Orthogonal contrast analysis revealed significant linear increases in DM digestibility (P = 0.049), energy digestibility (P = 0.015), and fat digestibility (P < 0.001) with increasing levels of 1,3-DAG supplementation, with no significant quadratic responses observed for these variables.
Table 3.
Effects of dietary 1,3-diacylglycerol supplementation on nutrient digestibility in broiler chickens.
| Treatment |
PC vs NC | Linear | Quadratic | ||||||
|---|---|---|---|---|---|---|---|---|---|
| PC | NC | T1 | T2 | SEM | P-value | P-value | P-value | P-value | |
| DM, % | 71.78 | 70.56 | 71.39 | 72.77 | 0.76 | 0.278 | 0.312 | 0.049 | 0.770 |
| Nitrogen, % | 69.89 | 68.25 | 69.6 | 70.57 | 1.02 | 0.463 | 0.143 | 0.138 | 0.888 |
| Energy, % | 71.35 | 69.56 | 71.02 | 71.93 | 0.79 | 0.232 | 0.288 | 0.015 | 0.720 |
| Fat, % | 88.04 | 85.89 | 87.62 | 88.53 | 0.66 | 0.072 | 0.130 | <0.001 | 0.391 |
PC, positive control diet; NC, negative control diet with 100 kcal/kg reduced ME; T1, NC supplemented with 0.05% 1,3-diacylglycerol (DAG); T2, NC supplemented with 0.10% 1,3-DAG. SEM, standard error of the mean.
Orthogonal contrasts were used to determine the linear and quadratic effects of dietary 1,3-DAG supplementation (0, 0.05, and 0.10%) among NC, T1, and T2.
Nutrient retention and excretion
The effects of dietary treatments on nutrient retention and excretion are presented in Table 4. Nutrient intake was not affected by dietary treatment for DM, nitrogen, or energy (P > 0.05). However, fat intake was significantly higher in the NC group than in the PC group (P = 0.012). No significant differences were observed among treatments in nutrient retention (P > 0.05). In contrast, nutrient excretion was significantly affected by dietary treatment. Dry matter excretion was significantly lower in the 1,3-DAG-supplemented groups than in the NC group, and a significant linear decrease was observed with increasing levels of 1,3-DAG supplementation (P = 0.027). Similarly, nitrogen excretion was reduced by 1,3-DAG supplementation (P < 0.025). Energy excretion also showed a significant linear decrease with increasing 1,3-DAG levels (P < 0.026). Fat excretion was significantly affected by dietary treatment (P < 0.001). The NC group exhibited the highest fat excretion, whereas 1,3-DAG supplementation reduced fat excretion in a dose-dependent manner. No significant quadratic responses were observed for DM, nitrogen, energy, or fat excretion.
Table 4.
Effects of dietary 1,3-diacylglycerol supplementation on nutrient retention and excretion in broiler chickens.
| Treatment |
PC vs NC | Linear | Quadratic | ||||||
|---|---|---|---|---|---|---|---|---|---|
| PC | NC | T1 | T2 | SEM | P-value | P-value | P-value | P-value | |
| Feed intake, g/d | 107.8 | 108.7 | 106.6 | 107.8 | 2.51 | 0.947 | 0.696 | 0.820 | 0.623 |
| DM intake, g/d | 95.0 | 96.0 | 94.2 | 95.3 | 2.22 | 0.947 | 0.638 | 0.820 | 0.624 |
| Nitrogen intake, g/d | 3.45 | 3.48 | 3.41 | 3.45 | 0.08 | 0.952 | 0.686 | 0.819 | 0.639 |
| Energy intake, kcal/d | 344.8 | 336.9 | 330.4 | 334.3 | 7.81 | 0.619 | 0.310 | 0.820 | 0.623 |
| Fat intake, g/d | 4.02 | 4.33 | 4.24 | 4.29 | 0.10 | 0.177 | 0.012 | 0.828 | 0.613 |
| Retention | |||||||||
| DM, g/d | 68.2 | 67.8 | 67.2 | 69.3 | 1.59 | 0.814 | 0.752 | 0.519 | 0.547 |
| Nitrogen, g/d | 2.41 | 2.37 | 2.38 | 2.44 | 0.06 | 0.823 | 0.478 | 0.448 | 0.697 |
| Energy, kcal/d | 246.0 | 234.4 | 234.6 | 240.4 | 5.56 | 0.429 | 0.060 | 0.469 | 0.713 |
| Fat, g/d | 3.54 | 3.72 | 3.72 | 3.80 | 0.09 | 0.243 | 0.058 | 0.519 | 0.737 |
| Excretion | |||||||||
| DM, g/d | 26.82 | 28.27 | 26.94 | 25.94 | 0.69 | 0.120 | 0.043 | 0.027 | 0.842 |
| Nitrogen, g/d | 1.04 | 1.11 | 1.04 | 1.01 | 0.03 | 0.079 | 0.019 | 0.025 | 0.512 |
| Energy, kcal/d | 98.8 | 102.6 | 95.8 | 93.8 | 2.49 | 0.079 | 0.122 | 0.026 | 0.429 |
| Fat, g/d | 0.48b | 0.61a | 0.52b | 0.49b | 0.01 | <.0001 | <0.001 | <0.001 | 0.106 |
PC, positive control diet; NC, negative control diet with 100 kcal/kg reduced ME; T1, NC supplemented with 0.05% 1,3-diacylglycerol (DAG); T2, NC supplemented with 0.10% 1,3-DAG. SEM, standard error of the mean.
Means within a row with different superscripts differ significantly at P < 0.05. Orthogonal contrasts were used to determine the linear and quadratic effects of dietary 1,3-DAG supplementation (0, 0.05, and 0.10%) among NC, T1, and T2.
Blood lipid profiles
The effects of dietary treatments on serum lipid profiles are presented in Table 5. Serum concentrations of triglycerides, total cholesterol, HDL-cholesterol, and LDL-cholesterol were not affected by dietary treatment (P > 0.05). In addition, no significant linear or quadratic effects of dietary 1,3-DAG supplementation were observed for any of the measured parameters (P > 0.05).
Table 5.
Effects of dietary 1,3-diacylglycerol supplementation on blood lipid profiles in broiler chickens.
| Treatment |
PC vs NC | Linear | Quadratic | ||||||
|---|---|---|---|---|---|---|---|---|---|
| PC | NC | T1 | T2 | SEM | P-value | P-value | P-value | P-value | |
| Triglyceride, mg/dL | 90.3 | 89.8 | 87.5 | 83.0 | 3.35 | 0.437 | 0.935 | 0.128 | 0.768 |
| Total cholesterol, mg/dL | 140.5 | 136.8 | 133.5 | 129.0 | 6.54 | 0.653 | 0.778 | 0.345 | 0.932 |
| HDL-cholesterol, mg/dL | 46.3 | 43.8 | 45.8 | 48.3 | 2.83 | 0.738 | 0.587 | 0.280 | 0.946 |
| LDL-cholesterol, mg/dL | 76.0 | 75.0 | 70.0 | 64.0 | 7.84 | 0.695 | 0.948 | 0.284 | 0.956 |
PC, positive control diet; NC, negative control diet with 100 kcal/kg reduced ME; T1, NC supplemented with 0.05% 1,3-diacylglycerol (DAG); T2, NC supplemented with 0.10% 1,3-DAG. SEM, standard error of the mean.
HDL, high-density lipoprotein; LDL, low-density lipoprotein.
Orthogonal contrasts were used to determine the linear and quadratic effects of dietary 1,3-DAG supplementation (0, 0.05, and 0.10%) among NC, T1, and T2.
Rectal temperature
The effects of dietary treatments on rectal temperature are presented in Table 6. Rectal temperature was not affected by dietary treatment (P > 0.05). In addition, no significant linear or quadratic effects of dietary 1,3-DAG supplementation were observed (P > 0.05).
Table 6.
Effects of dietary 1,3-diacylglycerol supplementation on rectal temperature in broiler chickens.
| Treatment |
PC vs NC | Linear | Quadratic | ||||||
|---|---|---|---|---|---|---|---|---|---|
| PC | NC | T1 | T2 | SEM | P-value | P-value | P-value | P-value | |
| Rectal temperature, °C | 41.8 | 41.6 | 41.7 | 41.7 | 0.22 | 0.942 | 0.551 | 0.670 | 0.962 |
PC, positive control diet; NC, negative control diet with 100 kcal/kg reduced ME; T1, NC supplemented with 0.05% 1,3-diacylglycerol (DAG); T2, NC supplemented with 0.10% 1,3-DAG. SEM, standard error of the mean.
Orthogonal contrasts were used to determine the linear and quadratic effects of dietary 1,3-DAG supplementation (0, 0.05, and 0.10%) among NC, T1, and T2.
Discussion
The present study demonstrated that dietary supplementation with 1,3-DAG improved feed efficiency in broilers fed reduced-energy diets containing PKM. This finding is consistent with previous reports showing that PKM inclusion can impair performance, particularly feed efficiency, due to its relatively high fiber content, substantial NSP fraction, and lower nutrient availability compared with conventional cereal–soybean meal diets (Sundu et al., 2006). For example, Yaophakdee et al. (2018) reported that broilers fed low levels of PKM (5 and 7.5% in starter and grower diets) showed no differences in BWG, FI, or FCR over 35 days, whereas higher inclusion levels (10 and 15%) impaired feed efficiency. Similarly, Abdollahi et al. (2016) observed reductions in BWG and FI when PKM was included at 24% in broiler diets. In the current study, the detrimental effect of the NC diet was expressed mainly in FCR rather than BWG or FI, suggesting that the primary limitation of the reduced-energy PKM diet was inefficient nutrient utilization rather than reduced voluntary feed consumption.
A notable finding of the present study was that 1,3-DAG supplementation improved BWG and FCR in a dose-dependent manner, particularly during the grower and finisher phases, and restored overall BWG and FCR in T2 to a level comparable to that of the PC group. Because FI was not affected by dietary treatment, the improvement in BWG and FCR likely resulted from enhanced utilization of ingested nutrients rather than increased FI. This interpretation is consistent with previous studies reporting beneficial effects of dietary lysophospholipids (Zhao and Kim, 2017), a blend of sodium stearoyl-2-lactylate and 1,3-DAG (Liu et al., 2020), and a lysophospholipid–polyethylene glycol ricinoleate blend (Ahmadi-Sefat et al., 2022) on BWG and FCR in broilers, particularly under reduced-energy dietary conditions. Emulsifiers improve the dispersion of dietary lipids in the intestinal lumen, promote the formation of smaller fat droplets, and enhance micelle formation, thereby increasing the accessibility of lipids to lipase and improving fat absorption (Adli et al., 2026). In this context, the positive response to 1,3-DAG in the present study suggests that emulsification became nutritionally meaningful under the reduced-energy PKM-based feeding condition.
The digestibility data support this explanation. Although the overall treatment effect was not significant for DM, nitrogen, energy, or fat digestibility, orthogonal contrast analysis revealed significant linear increases in DM, energy, and fat digestibility with increasing dietary 1,3-DAG levels. Among these, the response in fat digestibility was the clearest. This is biologically relevant because PKM is not only a fibrous ingredient but also a by-product containing residual oil that may not be efficiently utilized by broilers. Previous studies have indicated that the nutritional limitation of PKM is related not simply to its lower energy density, but also to the structural entrapment of nutrients, including lipids, within fibrous cell wall components rich in mannans and other NSP fractions (Choi et al., 2021). Consistent with the present findings, previous studies have demonstrated that various dietary emulsifiers improve nutrient digestibility in broilers. Ahmadi-Sefat et al. (2022) reported that supplementation with a lysophospholipid blend linearly increased the apparent ileal digestibility of DM, crude protein, crude fat, ash, and energy, with more pronounced effects in low-energy diets. Furthermore, Jansen et al. (2015) demonstrated that dietary lysolecithin improved DM digestibility, whereas Kamran et al. (2020) reported significant increases in both DM and crude fat digestibility following supplementation with polyglycerol polyricinoleate. Therefore, the linear increase in fat digestibility observed in the present study suggests that 1,3-DAG supplementation improved access to and utilization of this lipid fraction, thereby partially compensating for the reduced dietary energy density of the NC diet.
The nutrient retention and excretion results provide additional mechanistic support for this interpretation. Nutrient retention values were not significantly altered by treatment, but excretion of DM, nitrogen, energy, and especially fat was reduced by 1,3-DAG supplementation. Most importantly, the NC group showed significantly higher fat intake than the PC group, yet also exhibited the greatest fat excretion. This pattern indicates that a greater amount of dietary fat entered the digestive tract in the NC treatment, but a substantial proportion of that fat escaped digestion and was lost in the excreta. In contrast, 1,3-DAG supplementation reduced fat excretion in a dose-dependent manner, strongly suggesting improved digestion and absorption of dietary lipids. Because fat is a major contributor to dietary energy supply, the reduction in fat loss likely contributed directly to the improved BWG and FCR observed in 1,3-DAG-supplemented birds (Adli et al., 2026; Upadhaya et al., 2017).
Another important aspect of the present findings is that improvements in nutrient utilization were not accompanied by alterations in serum lipid profiles or rectal temperature. Serum concentrations of triglycerides, total cholesterol, HDL-cholesterol, and LDL-cholesterol were unaffected by treatment, indicating that 1,3-DAG supplementation did not markedly alter systemic lipid metabolism under the conditions of this study. The effects of dietary supplementation with different emulsifiers on serum lipid profiles in broilers have been inconsistent across studies. Some studies have reported reductions in serum LDL concentrations or improvements in lipoprotein profiles following supplementation with a sodium stearoyl-2-lactylate/Tween 20 blend (Upadhaya et al., 2018) or a sodium stearoyl-2-lactylate/1,3-DAG blend (Liu et al., 2020), whereas others have observed age-dependent or transient effects following supplementation with glyceryl polyethylene glycol ricinoleate (Roy et al., 2010). In contrast, several studies have reported no significant effects of dietary 1,3-DAG supplementation on serum lipid parameters, including triglycerides, free fatty acids, total cholesterol, HDL-C, and LDL-C (Upadhaya et al., 2017; Zhao et al., 2025). In this context, the absence of changes in serum lipid profiles in the present study suggests that the effect of 1,3-DAG supplementation was primarily localized to intestinal lipid digestion rather than systemic lipid metabolism. Likewise, rectal temperature was unchanged, indicating that the enhanced nutrient utilization associated with 1,3-DAG was not accompanied by increased metabolic heat production. These findings are important from a physiological standpoint, as they indicate that 1,3-DAG improved feed efficiency without imposing detectable metabolic or thermoregulatory stress on the birds, supporting the view that 1,3-DAG acts mainly within the digestive process rather than through broader metabolic alterations.
The present study has several limitations. The mechanisms underlying the improved nutrient utilization were not directly investigated. Therefore, further studies evaluating intestinal morphology, digestive enzyme activity, lipid metabolism-related gene expression, and gut microbiota composition are warranted.
Conclusion
In conclusion, dietary supplementation with 1,3-DAG improved feed efficiency in broilers fed reduced-energy diets containing PKM. The improvement in FCR was primarily associated with enhanced lipid utilization, as evidenced by increased fat digestibility and reduced fat excretion. Importantly, these effects were achieved without changes in serum lipid profiles or rectal temperature, indicating no adverse physiological responses. Therefore, 1,3-DAG supplementation may serve as an effective nutritional strategy to improve the utilization of PKM-based reduced-energy diets in broiler production.
Funding
This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (NRF-RS-2023-00275307).
CRediT authorship contribution statement
J.H. Park: Writing – original draft, Software, Resources, Investigation, Formal analysis, Data curation, Conceptualization. I.H. Kim: Writing – review & editing, Visualization, Validation, Supervision, Project administration, Funding acquisition.
Disclosures
The authors declare no conflicts of interest regarding the research, authorship, or publication of this article.
References
- Abdollahi M.R., Hosking B.J., Ning D., Ravindran V. Influence of palm kernel meal inclusion and exogenous enzyme supplementation on growth performance, energy utilization, and nutrient digestibility in young broilers. Asian-Australas. J. Anim. Sci. 2016;29:539–548. doi: 10.5713/ajas.15.0224. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Adli D.N., Sugiharto S., Ujilestari T., Irawan A., Azmi A.F.M., Illaningtyas F., Wahyuni D.S., Qomariyah N., Sitaresmi P.I., Krisnan R., Purba R.D., Matitaputty P.R., Alifian M.D., Sholikin M.M. Emulsifiers in poultry nutrition–molecular mechanism of lipid metabolism and energy utilization: a meta-analysis and KEGG mapping. Poult. Sci. 2026;105 doi: 10.1016/j.psj.2026.106603. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Ahmadi-Sefat A.A., Taherpour K., Ghasemi H.A., Gharaei M.A., Shirzadi H., Rostami F. Effects of an emulsifier blend supplementation on growth performance, nutrient digestibility, intestinal morphology, and muscle fatty acid profile of broiler chickens fed diets with different levels of energy and protein. Poult. Sci. 2022;101 doi: 10.1016/j.psj.2022.102145. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Alimon A.R. The nutritive value of palm kernel cake for animal feed. Palm. Oil Dev. 2004;40:12–14. [Google Scholar]
- Alshelmani M.I., Loh T.C., Foo H.L., Sazili A.Q., Lau W.H. Effect of feeding different levels of palm kernel cake fermented by paenibacillus polymyxa ATCC 842 on nutrient digestibility, intestinal morphology, and gut microflora in broiler chickens. Anim. Feed Sci. Technol. 2016;216:216–224. doi: 10.1016/j.anifeedsci.2016.03.019. [DOI] [Google Scholar]
- AOAC . 17th ed. Assoc. Off. Anal. Chem.; Arlington, VA: 2001. Official Methods of Analysis. [Google Scholar]
- Azizi M.N., Loh T.C., Foo H.L., Chung E.L.T. Is palm kernel cake a suitable alternative feed ingredient for poultry? Animals. 2021;11:338. doi: 10.3390/ani11020338. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Choi W.J., Kim J.H., Kim H.W., Kim K.E., Kil D.Y. Effects of dietary palm kernel meal and β-xylanase on productive performance, fatty liver incidence, and excreta characteristics in laying hens. J. Anim. Sci. Technol. 2021;63:1275–1285. doi: 10.5187/jast.2021.e111. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Jansen M., Nuyens F., Buyse J., Leleu S., Van Campenhout L. Interaction between fat type and lysolecithin supplementation in broiler feeds. Poult. Sci. 2015;94:2506–2515. doi: 10.3382/ps/pev181. [DOI] [PubMed] [Google Scholar]
- Kamran J., Mehmood S., Mahmud A. Effect of fat sources and emulsifier levels in broiler diets on performance, nutrient digestibility, and carcass parameters. Braz. J. Poult. Sci. 2020;22 doi: 10.1590/1806-9061-2019-1158. eRBCA-2019. [DOI] [Google Scholar]
- Liu X., Yun K.S., Kim I.H. Evaluation of sodium stearoyl-2-lactylate and 1,3-diacylglycerol blend supplementation in diets with different energy content on growth performance, meat quality, nutrient digestibility, and blood lipid profiles of broiler chickens. J. Poult. Sci. 2020;57:55–62. doi: 10.2141/jpsa.0190007. [DOI] [PMC free article] [PubMed] [Google Scholar]
- McClements D.J., Jafari S.M. Improving emulsion formation, stability, and performance using mixed emulsifiers: a review. Adv. Colloid Interface Sci. 2018;251:55–79. doi: 10.1016/j.cis.2017.12.001. [DOI] [PubMed] [Google Scholar]
- National Institute of Animal Science . Jeonju; Republic of Korea: 2022. Korean Feeding Standard for Poultry. Rural Development Administration. [Google Scholar]
- National Research Council . National Academies Press; Washington, DC: 1994. Nutrient Requirements of Poultry, 9th Rev. [Google Scholar]
- Panigrahi S., Powell C.J. Effects of high rates of inclusion of palm kernel meal in broiler chick diets. Anim. Feed Sci. Technol. 1991;34:37–47. doi: 10.1016/0377-8401(94)90190-2. [DOI] [Google Scholar]
- Roy A., Haldar S., Mondal S., Ghosh T.K. Effects of supplemental exogenous emulsifier on performance, nutrient metabolism, and serum lipid profile in broiler chickens. Vet. Med. Int. 2010;2010:1–9. doi: 10.4061/2010/262604. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Sharmila A., Alimon A.R., Azhar K., Noor H.M., Samsudin A.A. Improving nutritional values of palm kernel cake (PKC) as poultry feeds: a review. Mal. J. Anim. Sci. 2014;17:1–18. [Google Scholar]
- Sundu B., Kumar A., Dingle J. Palm kernel meal in broiler diets: effect on chicken performance and health. Worlds Poult. Sci. J. 2006;62:316–325. doi: 10.1079/WPS2005100. [DOI] [Google Scholar]
- Upadhaya S.D., Park J.W., Park J.H., Kim I.H. Efficacy of 1,3-diacylglycerol as a fat emulsifier in low-density diet for broilers. Poult. Sci. 2017;96:1672–1678. doi: 10.3382/ps/pew425. [DOI] [PubMed] [Google Scholar]
- Upadhaya S.D., Lee J.S., Jung K.J., Kim I.H. Influence of emulsifier blends having different hydrophilic–lipophilic balance value on growth performance, nutrient digestibility, serum lipid profiles, and meat quality of broilers. Poult. Sci. 2018;97:255–261. doi: 10.3382/ps/pex303. [DOI] [PubMed] [Google Scholar]
- Upadhaya S.D., Yun K.S., Zhao P.Y., Lee I.S., Kim I.H. Emulsifier as a feed additive in poultry and pigs: a review. Anim. Nutr. Feed Technol. 2019;19:323–336. doi: 10.5958/0974-181X.2019.00030.1. [DOI] [Google Scholar]
- Yaophakdee N., Ruangpanit Y., Attamangkune S. Effects of palm kernel meal level on live performance and gut morphology of broilers. Agric. Nat. Resour. 2018;52:75–78. doi: 10.1016/j.anres.2018.05.007. [DOI] [Google Scholar]
- Zhao P.Y., Kim I.H. Effect of diets with different energy and lysophospholipids levels on performance, nutrient metabolism, and body composition in broilers. Poult. Sci. 2017;96:1341–1347. doi: 10.3382/ps/pew469. [DOI] [PubMed] [Google Scholar]
- Zhao W.H., Jang S.Y., Kim I.H. Optimizing broiler performance and feed cost efficiency: impact of 1,3-diacylglycerol supplementation at different energy levels. Vet. Sci. 2025;12:633. doi: 10.3390/vetsci12070633. [DOI] [PMC free article] [PubMed] [Google Scholar]