DISCUSSION

Effects of emulsifier supplementation on growth performance during the starter phase

The present study investigated the effects of emulsifier supplementation at different dietary inclusion levels on the performance of broilers during the starter phase (1–10 days). The improvements in BW and feed efficiency observed during this phase suggest enhanced nutrient utilization, particularly of dietary lipids. These findings are consistent with previous studies demonstrating that emulsifier supplementation improves fat digestion and energy availability in young broilers with immature digestive systems. The greater response observed during early life may be explained by limited endogenous bile secretion and lipase activity at this developmental stage. The numerical improvement in digestibility observed in the present study may be attributable to enhanced fat digestion, which agrees with previous reports [5].

Emulsifier supplementation has been reported to improve FI and BW in broilers during the starter phase. Furthermore, the inclusion of emulsifiers has been associated with improved FCR, indicating more efficient conversion of feed into body mass, which is a critical factor in the economic production of broilers [25]. Emulsifiers improve lipid digestion by reducing the surface tension between dietary lipids and the aqueous phase of the digesta, thereby facilitating emulsification, micelle formation, and increasing the accessibility of lipids to digestive enzymes [26]. Consequently, dietary energy utilization is enhanced, particularly in energy-deficient diets such as T2, which contained 150 kcal/kg less ME than the PC diet.

The early-phase response observed in the present study may also be related to the complementary functions of the emulsifier components. Sorbitan esters act as non-ionic emulsifiers and may improve the dispersion of dietary lipid droplets, thereby increasing the surface area available for enzymatic hydrolysis. Lysolecithin, a lysophospholipid-rich component, may further facilitate micelle formation and lipid absorption, whereas de-oiled lecithin provides phospholipids that contribute to emulsion stability and lipid transport [26]. These complementary mechanisms may be particularly beneficial in young broilers whose endogenous lipid digestion capacity is not fully developed. The absence of treatment effects on FI further supports the hypothesis that improvements in growth performance were primarily attributable to enhanced nutrient absorption rather than increased feed consumption.

In addition, emulsifiers facilitate the digestion and absorption of dietary fats through several physiological and biochemical mechanisms that optimize nutrient utilization. Previous studies have also reported increased lipase activity following emulsifier supplementation, which enhances the hydrolysis of dietary fats into absorbable fatty acids and contributes to improved growth performance [5]. However, direct evidence regarding the efficacy of sorbitan esters in broiler nutrition remains limited. Therefore, the present findings should be considered preliminary evidence supporting the efficacy of this specific ternary emulsifier blend rather than confirmation of the independent contribution of each emulsifier component.

Comparison with previous multi-component emulsifier systems

Previous investigations of multi-component emulsifier systems have primarily focused on combinations of lysolecithin, synthetic emulsifiers, and monoglycerides. For example, Ghazalah et al. [12] reported improvements in growth performance, intestinal morphology, and selected carcass traits in broilers fed low-energy diets supplemented with such combinations. In contrast, the present study evaluated a ternary blend containing sorbitan esters in addition to phospholipid-based emulsifiers, potentially providing an additional non-ionic emulsification mechanism. This distinction is important because responses to emulsifier supplementation are strongly influenced by emulsifier composition, dietary formulation, lipid source, and bird age.

Effects of emulsifier supplementation during the grower and finisher phases

The greater BW observed during the grower phase in broilers receiving 200 and 250 g/ton emulsifier suggests improved nutrient utilization under reduced-energy conditions. This response may be attributed to enhanced lipid digestion and absorption, enabling the emulsifier to partially compensate for the dietary energy deficit and support growth performance.

In contrast, no significant treatment effects were observed during the finisher phase. This finding suggests that the response to emulsifier supplementation diminished as birds matured. The maturation of the digestive system, including increased endogenous secretion of bile salts and lipolytic enzymes, may reduce the dependence of older birds on exogenous emulsifiers [12]. Consequently, reducing emulsifier inclusion from 250 g/ton to 200 g/ton during the finisher phase did not adversely affect productive performance.

Phase-dependent response to emulsifier supplementation

The absence of significant differences in overall performance from 1 to 35 days despite significant responses during the starter and grower phases may be explained by the progressive maturation of lipid digestion in broilers. As birds age, increased secretion of bile salts and pancreatic lipase enhances endogenous digestive capacity and reduces dependence on exogenous emulsifiers. Furthermore, compensatory growth during the later stages of production may have reduced differences among treatments that were evident earlier in life. Therefore, the lack of significant overall responses should not be interpreted as evidence of inefficacy but rather as an indication that the benefits of emulsifier supplementation are phase-dependent.

Effects of emulsifiers on energy utilization

The use of emulsifiers in broiler diets has been shown to reduce dietary ME requirements while maintaining or enhancing productive performance. Previous studies have demonstrated that emulsifiers improve dietary fat digestibility, thereby allowing reductions in dietary energy without compromising growth performance [5]. The extent of energy reduction achievable depends on emulsifier type and dietary composition.

The inclusion of lecithin-based emulsifiers has previously allowed reductions in dietary ME while maintaining productive performance, suggesting that emulsifiers improve nutrient absorption and energy utilization efficiency [27]. Similarly, supplementation of emulsifiers in diets containing dietary oils reduced dietary ME requirements by 40 kcal/kg during days 1–21 and by 50 kcal/kg during days 22–49 while maintaining broiler performance during the early growth phase [28]. A meta-analysis further demonstrated that emulsifier supplementation increased weight gain by 1.62 g/day and reduced FCR by 0.04, confirming the effectiveness of emulsifiers in enhancing broiler performance under reduced-energy feeding programs [29].

Functional roles of lysolecithin and de-oiled lecithin

Lysolecithin, a hydrolyzed derivative of lecithin, has been extensively studied and shown to improve FCR, BW gain, and total tract digestibility of energy and ether extract, particularly in reduced-energy diets [12, 30]. In addition, lysolecithin increases the production of beneficial short-chain fatty acids in the cecum, thereby contributing to intestinal health [31]. Furthermore, lysolecithin supplementation has been associated with improved litter quality and reduced incidence of footpad lesions, reflecting positive effects on bird welfare [11].

De-oiled lecithin exhibits strong emulsifying properties and contributes to improvements in growth performance, FCR, and carcass characteristics. Previous studies have reported increased breast muscle yield and reduced abdominal fat deposition in broilers fed de-oiled lecithin-supplemented diets [32]. De-oiled lecithin has also been associated with improvements in lipid metabolism, including increased high-density lipoprotein concentrations and reduced low-density lipoprotein concentrations. Moreover, improvements in intestinal morphology, including greater jejunal villus height and villus-to-crypt ratios, have been reported [33]. Reduced E. coli counts in excreta have also been observed, suggesting a beneficial role in maintaining gut microbial balance and intestinal health [32].

Although both lysolecithin and de-oiled lecithin have demonstrated substantial benefits, their efficacy may vary depending on dietary fat source, dietary energy concentration, and production objectives. Their benefits are generally more pronounced in reduced-energy diets, where enhanced nutrient utilization compensates for reduced-energy availability. However, under standard- or high-energy feeding conditions, their effects may be less evident. Therefore, practical application should consider production goals, economic factors, and physicochemical characteristics such as hydrophilic-lipophilic balance (HLB) and compatibility with dietary ingredients [10].

Feed digestibility and AME responses

Although emulsifier supplementation numerically increased AME compared with the NC treatment, total tract digestibility and OM digestibility were not significantly affected. Therefore, the present results do not provide direct evidence that the emulsifier blend improved fat digestibility. Nevertheless, the numerical increase in AME may indicate partial improvement in energy utilization, which is consistent with the recognized role of emulsifiers in lipid dispersion and micelle formation. Future studies should include measurements of ether extract digestibility, ileal digestibility, and fatty acid digestibility to determine whether the observed increase in AME is directly associated with improved lipid utilization.

Gastrointestinal retention time

Reducing dietary ME by 150 kcal/kg influenced gastrointestinal retention time, whereas supplementation with 200 g/ton emulsifier significantly reduced retention time. The longer retention time observed in the PC group may partly reflect its greater energy density and lower fiber concentration compared with the reduced-energy diets. In contrast, the NC diets contained higher levels of rice solvent bran and dietary fiber, which may have accelerated digesta passage.

The physiological mechanisms influencing retention time are closely associated with digestive efficiency, particularly lipid digestion and nutrient absorption. Improved nutrient digestibility, especially lipid utilization, may reduce retention time because nutrients are absorbed more rapidly and efficiently [34]. Emulsifiers can enhance dietary fat emulsification and absorption, thereby increasing digestive efficiency and potentially accelerating digesta passage through the gastrointestinal tract [3, 35]. However, this interpretation remains speculative because digesta passage kinetics and fat-specific digestibility were not directly evaluated.

The greater fiber concentration in the reduced-energy diets may also have contributed to the observed retention time responses. In the present study, the reduced-energy diets contained 1.06%–1.07% more fiber than the PC diet. High-fiber diets have been reported to decrease digesta retention time and increase passage rate through the gastrointestinal tract, which may reduce ME retention and dry matter metabolizability, particularly in diets containing fibrous ingredients such as wheat bran and oat hulls [36]. Therefore, the observed retention time response likely reflects the combined effects of dietary energy density, fiber concentration, and emulsifier supplementation rather than the effect of emulsifier supplementation alone.

Fecal characteristics

Fecal scores did not differ significantly among treatments, indicating that reduced-energy diets and emulsifier supplementation did not adversely affect fecal consistency under the conditions of the present study. Although fecal score may indirectly reflect litter quality and bird welfare, litter moisture and footpad condition were not evaluated. Therefore, no definitive conclusions regarding welfare outcomes can be drawn from the present results.

Carcass characteristics

Emulsifier supplementation in reduced-energy diets improved carcass yield to values comparable with those of the PC treatment without adversely affecting carcass component proportions or abdominal fat deposition. These findings suggest that emulsifiers can support muscle accretion and overall carcass development under reduced-energy feeding conditions.

The lower carcass yield observed in T2 (84.28%) compared with T1 (85.81%) is likely attributable to the reduction of 150 kcal/kg dietary ME, which may have limited growth potential and carcass deposition. In contrast, T5 (84.85%) exhibited numerically greater carcass yield than T2, suggesting that emulsifier supplementation partially restored carcass productivity. Previous studies have similarly reported increased carcass weight and carcass yield in broilers receiving emulsifier supplementation [12]. Improved energy utilization resulting from emulsifier supplementation may enhance protein and lipid metabolism, thereby supporting muscle development and increasing carcass yield [7]. Furthermore, emulsifiers may reduce fat excretion, resulting in more efficient utilization of dietary lipids and greater nutrient retention within muscle tissue rather than excreta [4].

Practical implications of the study

The present study was conducted under tropical environmental conditions in Thailand, where elevated ambient temperature and humidity may negatively affect FI, nutrient utilization, and growth performance. Under these conditions, reducing dietary ME by 150 kcal/kg represented a practical nutritional challenge. The significant responses observed during the starter and grower phases suggest that the ternary emulsifier blend may partially support energy utilization in reduced-energy diets, particularly when young broilers possess limited digestive capacity. However, because these responses were not maintained through market age, the benefits of emulsifier supplementation should be interpreted as phase-dependent rather than continuous throughout the production cycle.

The practical relevance of the study is further strengthened by the use of palm oil and rice solvent bran, which are commonly used feed ingredients in Southeast Asian poultry production systems. The greater fiber concentration of the NC diet increased the challenge to nutrient utilization, whereas the inclusion of palm oil provided a commercially relevant model for evaluating emulsifier supplementation. Although the observed responses in gastrointestinal retention time and carcass yield suggest alterations in nutrient utilization, direct measurements of fatty acid digestibility, intestinal morphology, blood lipid profiles, and digestive enzyme activity are required to elucidate the underlying mechanisms. FCG was included as an economic indicator; however, no significant differences were observed among treatments. Consequently, the present study cannot conclusively demonstrate economic advantages. Nevertheless, the phase-specific supplementation strategy may offer opportunities for cost optimization by reducing emulsifier inclusion during the finisher phase, although this requires validation through commercial-scale economic analyses using current ingredient and additive prices.