Effects of Non-Fermented Red Ginseng Marc in a Commercial Liquid Feeding System on Growth Performance, Fecal Short-Chain Fatty Acids, Blood Profiles, and Pork Quality in Growing Finishing Pigs

1. Introduction

Feed cost is the largest expense in pig production, accounting for approximately 60% to 70% of total production cost[1]. In recent years, geopolitical conflicts, supply-chain disruptions, and climate-related extreme events have increased uncertainty in global feed ingredient markets, leading to greater price volatility[2,3]. Under these conditions, the use of locally available alternative feed ingredients and agricultural by-products has become an important strategy to improve sustainability in pig production[4]. However, their nutritional value and biological effects must be carefully evaluated to ensure that their inclusion does not compromise growth performance under practical conditions.

Red ginseng marc (RGM) is a by-product of red ginseng processing, referring to the solid residue remaining after aqueous extraction and concentration following the washing, steaming, and drying of fresh ginseng[5,6]. Although most water-soluble active compounds are removed during processing, RGM still contains residual ginsenosides, polysaccharides, dietary fiber, and other normal nutrients[7]. Previous studies have shown that red ginseng by-products generally contain low moisture (4%–6%), moderate crude protein (13%–15%), low crude fat (0.8%–1.4%), and certain amounts of ash (4%–5%) and crude fiber (approximately 15%)[8,9]. These characteristics suggest that RGM may serve as a potential alternative feed ingredient, although its relatively high fiber content may influence nutrient utilization and gut fermentation in monogastric animals.

Most studies on red ginseng and its by-products in monogastric animals have been conducted in poultry [10,11], whereas information in pigs remains limited. Previous work has mainly focused on fermented red ginseng products or extracts. For example, Ao et al. [12] reported no significant improvement in growth performance in poultry supplemented with fermented red ginseng extract, although some immune responses were affected. Similarly, Kim et al. [13,14] observed limited effects of red ginseng marc on production performance in laying hens and broilers, with some changes in serum cholesterol. In pigs, Yin et al. [17] found no significant effects of fermented red ginseng marc or extract on growth performance in weaned piglets. Overall, these results suggest that the response to red ginseng by-products may depend on processing method, inclusion level, and animal species. In particular, information on the direct use of non-fermented RGM in pig diets remains scarce, especially at relatively high inclusion levels.

Most studies on red ginseng and its by-products in monogastric animals have been conducted in poultry[10,11]. Ao et al.[12] reported that supplementation of fermented red ginseng extract in broilers and laying hens did not improve productive performance or egg quality. Similarly, Kim et al.[13] reported that dietary supplementation with 0.5%, 1%, and 2% red ginseng marc in laying hens had limited effects on overall egg production and egg quality, but reduced serum total cholesterol at the 1% and 2% inclusion levels. In broilers, dietary supplementation with red ginseng marc up to 3% did not adversely affect growth performance, while 3% inclusion level was associated with reduced mortality and serum cholesterol[14]. However, in pigs, studies have mainly focused on fermented red ginseng marc or red ginseng extracts[15,16]. Yin et al.[17] reported that supplementation with fermented red ginseng marc or extract (4g/kg) had no significant effects on growth performance or blood parameters in weaned piglets. Compared with the previous studies, information on the direct use of non-fermented red ginseng marc in pig diets remains scarce, particularly at relatively high inclusion levels.

Liquid feeding has been widely adopted in commercial pig production and is known to affect feed intake, nutrient utilization, and growth performance[18]. In practice, this system depends on liquid-feeding equipment, where feed is mixed with water at a defined ratio, usually 1:3, and delivered through a pipeline system. Despite the relatively high cost of installation and operation, liquid feeding provides clear practical advantages for the use of agricultural by-products and alternative feed resources, mainly because these ingredients can be incorporated more conveniently under liquid-feeding conditions. On this basis, further studies are needed to improve the efficient use of agricultural by-products in liquid-feeding systems, with particular attention to ingredient selection, optimal inclusion levels, and whether fermentation could further enhance their feeding value.

Given the limited information on the direct inclusion of non-fermented RGM in pig diets, especially under liquid feeding conditions, the present study evaluated the effects of dietary RGM supplementation (up to 6%) in a commercial liquid feeding system on growth performance, nutrient digestibility, blood profiles, and pork quality in growing-finishing pigs.

2. Materials and Methods

2.1. Experimental Animals and management

All experimental procedures were approved by the Yanbian University Institutional Animal Care and Use Committee (YBU-YD2025080001). A total of 480 growing-finishing pigs ([Yorkshire × Landrace] × Duroc; initial BW 32.64 ± 0.12 kg) were used in a 12-week feeding trial conducted at a commercial pig farm of Yanbian Hengxing Animal Husbandry Development Co., Ltd. in Longjing, Yanbian, China. Pigs were allotted to a randomized complete block design based on sex and initial BW, with four dietary treatments, three replicate pens per treatment, and 40 pigs (20 barrows and 20 gilts) per pen. The experimental phases were divided into early growing (weeks 0-3), late growing (weeks 4-6), early finishing (weeks 7-9), and late finishing (weeks 10-12) phases.

2.2. Experimental Design and Diet

The dietary treatments were: Control, basal liquid diet; RGM 2, basal liquid diet supplemented with 2% red ginseng marc (RGM); RGM 3, basal liquid diet supplemented with 3% RGM; and RGM 6, basal liquid diet supplemented with 6% RGM. The red ginseng marc used in the present study was obtained as a by-product after hot-water extraction of red ginseng prepared from 6-year-old Panax ginseng Meyer roots. Fresh ginseng was steamed at 80–90°C for 3 h and dried at 50–80°C to produce red ginseng. The red ginseng was then extracted with circulating hot water at 75–90°C for 8 h, repeated three times, and the remaining solid residue was collected as red ginseng marc. The marc was dried and used as the experimental by-product source. Its analyzed chemical composition and ginsenoside profile are shown in Table 1.

A commercial feeding program routinely used on the farm was adopted as the basal diet. The commercial basal feed (mash) was first mixed with water at a 1:3 ratio in a bulk tank to prepare the liquid diet, and red ginseng marc was then added to the mixture. The liquid diets were freshly prepared daily and supplied through an automatic computer-controlled liquid feeding system three times daily at 08:00, 15:00, and 23:00 h. All nutrients in the experimental diets met or exceeded the nutrient requirements suggested by NRC[19]. The analyzed and calculated chemical composition of the experimental diets is presented in Table 2.

2.3. Growth performance

Body weight (BW) was measured at the beginning of the experiment and at the end of each phase. Feed intake was recorded on a pen basis throughout the experimental period. Based on BW and feed intake data, average daily gain (ADG), average daily feed intake (ADFI), and gain-to-feed ratio (G: F) were calculated for each phase and for the overall 12-week period.

2.4. Nutrient digestibility and nitrogen retention

A total of 16 growing barrows (32.0 ± 0.86 kg) were allotted to one of the four dietary treatments with four pigs per treatment and housed in metabolic crates. The experimental liquid feed (feed : water = 1:3) were fed to pigs 3 times a day at 8:00, 15:00, and 23:00 with limited access to water according to the rate of 2 times the maintenance requirement for ME (106 kcal of ME per kg of BW0.75; NRC, 2012) based on the initial BW of pigs. After 7 days of adaptation, feces and urine samples were collected for 5 days using ferric oxide and chromium oxide as initial and end markers, respectively. Collected excreta were frozen immediately at −20°C for the collection period, dried (60°C, 72 h) in an air-drying oven, and ground (5-mm screen, Wiley mill) for chemical analysis at the end of the trial. Urine samples were also collected daily in a plastic container with 50 mL of 10% H2SO4 to avoid evaporation of ammonia from urine, and glass wool was used as a filter to remove foreign materials. The collected urine from each pig was brought to a final volume of 4,000 mL with water and mixed thoroughly. The representative samples were collected in 50 mL conical tubes and frozen at −20°C for nitrogen retention analysis.

2.5. Sample collection

Blood samples were collected from the jugular vein of 10 pigs per treatment at weeks 3, 6, 9, and 12.The blood samples were centrifuged for 15 min at 3,000 rpm and 4 °C (centrifuge 5810R; Eppendorf, Hamburg, Germany). The serum was transferred to 1.5 mL plastic tubes (serum tubes, BD vacutainer SSTTMII advance; Becton-Dickinson, London, UK) and stored at −20 °C until analysis. Fecal samples were collected directly from the rectum at each phase, stored at −20°C, and used for short-chain fatty acid (SCFA) analysis. At the end of the feeding period, pigs remained on their respective diets for an additional 2 weeks until they reached market weight. Thereafter, four pigs per treatment with similar body weight were selected for slaughter, and longissimus dorsi samples were collected near the 10th rib on the right side of the carcass for meat quality analysis.

2.6. Laboratory analyses

Samples of red ginseng marc, experimental diets, feces, urine, and pork were analyzed according to AOAC [20] procedures. Moisture, crude protein, crude fat, crude ash, calcium, and total phosphorus were determined for red ginseng marc and the experimental diets. Ginsenosides in red ginseng marc were analyzed by high-performance liquid chromatography (HPLC). Serum IgG and IgA concentrations were analyzed by ELISA assay by the manufacturer's protocols (ELISA Starter 87 Accessory Package, Pig IgG ELISA Quantitation Kit, Pig IgA ELISA Quantitation Kit; Bethyl, 88 Montgomery, AL, USA). Serum AST, ALT, BUN, total cholesterol, creatinine, and glucose concentration were analyzed using a blood chemistry analyzer (Cobas 8000, Roche, Germany). Fecal SCFA concentrations were determined after metaphosphoric acid extraction using gas chromatography with flame ionization detection and were expressed as μmol/g fresh feces. Meat pH and color were measured at 0, 3, 6, 12, and 24 h postmortem. The pH was determined using a portable pH meter (Model 720; Thermo Orion, Fullerton, CA, USA). Meat color was evaluated based on Commission Internationale de l’Eclairage (CIE) L*, a*, and b* values using a colorimeter (CR300; Minolta Camera Co., Osaka, Japan). Water-holding capacity (WHC) was determined by the centrifugation method. Briefly, the pork sample was ground, placed in a filter tube, heated in a water bath at 80°C for 20 min, and centrifuged at 2,688×g for 10 min at 10°C. For TBARS analysis, 3 g of sample was homogenized with 9 mL of distilled water and butylated hydroxytoluene solution, and the homogenate was reacted with thiobarbituric acid/trichloroacetic acid solution. After heating, cooling, and centrifugation, the absorbance of the supernatant was measured at 532 nm using a spectrophotometer. Cooking loss was determined by heating pork samples in a water bath until the internal temperature reached 72°C and calculating the difference in sample weight before and after cooking. Shear force was measured using core samples obtained parallel to the muscle fiber direction with a Warner–Bratzler shear device.

2.8. Statistical analyses

Data were analyzed using the MIXED procedure of SAS[21]. Pen was considered the experimental unit for growth performance, whereas the individual pig was considered the experimental unit for digestibility, fecal SCFA, blood profiles, carcass traits, and meat quality measurements. Orthogonal polynomial contrasts were used to evaluate the linear and quadratic effects of increasing dietary RGM supplementation. Results are presented as means and standard error of the mean (SEM). Statistical significance was declared at p<0.05, and 0.05≤p<0.10 was considered a tendency.

3. Results

3.1. Growth performance

The effects of dietary red ginseng marc (RGM) on growth performance are presented in Table 3. The final BW decreased linearly with increasing dietary red ginseng marc supplementation (p=0.05). ADG during weeks 10 to 12 showed both linear and quadratic responses (p=0.02 and p=0.02, respectively), and the lowest value was observed in the RGM 6 group. Overall, ADG also decreased linearly during the experimental period (p=0.03). ADFI decreased linearly during weeks 4 to 6 (p=0.01), 7 to 9 (p=0.02), 10 to 12 (p=0.01), and 0 to 12 weeks (p=0.05). G:F ratio during weeks 10 to 12 showed a quadratic response (p=0.04).

3.2. Nutrient digestibility and nitrogen retention

The effects of dietary RGM on nutrient digestibility and nitrogen retention are presented in Table 4. Dietary RGM supplementation did not affect the apparent total tract digestibility of dry matter, crude protein, crude fat, or crude ash. Nitrogen retention was also not influenced by dietary treatment.

3.3. Fecal short-chain fatty acids (SCFA)

The effects of dietary RGM supplementation on fecal SCFA concentrations are presented in Table 5. During the early finishing phase (weeks 7–9), acetate and butyrate increased linearly with increasing RGM levels (p=0.05 and p=0.03, respectively). In contrast, during the late finishing phase (weeks 10–12), acetate and propionate decreased linearly (p=0.04), while butyrate showed both linear and quadratic responses (p<0.05), with the lowest value observed in the RGM6 group. Total SCFA also showed a linear response to increasing dietary RGM levels (p=0.04).

3.4. Blood profiles

The effects of red ginseng marc levels on blood profiles are presented in Table 6. Serum ALT increased linearly at 3, 6, and 12 weeks (p=0.04; p=0.02; p=0.05, respectively). Serum glucose increased linearly at 9 and 12 weeks (p=0.04 and p=0.02, respectively). By contrast, serum BUN decreased linearly with increasing dietary RGM at 3, 6, and 12 weeks (p = 0.04, p = 0.05, and p = 0.04, respectively). Total cholesterol decreased linearly at 12 weeks (p=0.04).

3.5. Carcass traits

The effects of red ginseng marc levels on the carcass traits are presented in Table 7. The moisture, crude protein, crude ash, cooking loss, shear force, water-holding capacity, and TBARS were not affected by treatment.

3.6. Meat quality

The effects of dietary RGM on meat quality are presented in Table 8 and Table 9. Postmortem pH at 0 h showed a tendency to decrease linearly with increasing RGM levels (p=0.07). However, dietary RGM supplementation did not affect meat color at any measured times.

4. Discussion

In the present study, differences in growth performance were primarily observed during the late finishing phase, with a clear negative response in pigs fed 6% RGM. Previous studies have reported inconsistent effects of red ginseng or its by-products on growth performance. Yin et al.[17]observed no significant effects on BW, ADG, or G:F in weaned piglets supplemented with fermented red ginseng marc or extract. Similarly, Ao et al.[22]reported no improvement in ADG or G:F in finishing pigs fed fermented red ginseng. In contrast, Zhang et al.[23] found improved ADG with low-level inclusion (0.1%) of fermented red ginseng in growing-finishing pigs. These discrepancies are likely associated with ginseng products, differences in inclusion level and processing method (fermented or non-fermented), and feeding stages. In particular, the use of unfermented RGM at the high inclusion level of 6% in the present study negatively affected BW and ADG.

The reduction in ADFI appears to be the primary factor leading to the decreased final BW and ADG, particularly in pigs fed 6% RGM. One possible explanation is higher inclusion levels of RGM could reduce the diet palatability. Pigs are sensitive to taste, generally preferring sweet flavors while avoiding bitter compounds. Ginsenosides such as Rb1, Rg2, Rb3, and Rf are known to contribute to the bitter and astringent taste of ginseng-derived materials[24]. As the red ginseng marc used in the present study was not fermented, the lack of fermentation-related flavor may have limited its ability to mask the bitterness of residual saponins, thereby contributing to reduced voluntary feed intake during prolonged feeding at higher inclusion levels. This interpretation is partly supported by Ao et al.[22], who observed lower ADFI in finishing pigs fed 0.4% fermented red ginseng than in those fed 0.2% during the late finishing period. Another possible explanation relates to the fiber content of RGM. Because the material was not fermented, its fiber fraction may have increased dietary bulk and viscosity when mixed with water under liquid feeding conditions. This may have enhanced satiety and limited feed intake during prolonged feeding. Under liquid feeding systems, dietary fiber and residual bioactive compounds may interact to influence feeding behavior, gastric emptying, and satiety regulation, thereby collectively affecting voluntary feed intake. Importantly, no evidence of toxicity was observed, as no mortality or severe health issues occurred, and blood parameters remained within physiological ranges. Therefore, the reduction in feed intake with increasing RGM supplementation may be partly attributed to reduced diet palatability and increased dietary bulk under liquid feeding conditions.

The present results showed that red ginseng marc supplementation under liquid feeding conditions did not significantly affect nutrient digestibility or nitrogen retention. This indicates that RGM did not affect digestive efficiency under liquid feeding in this study. Previous studies have reported that fermented red ginseng or fermented red ginseng marc may improve the apparent total tract digestibility of dry matter or nitrogen in pigs[17,23]. However, these effects are likely associated with fermentation, which can enhance nutrient availability and reduce structural fiber. In contrast, both the red ginseng marc and the liquid diets used in the present study were not fermented, which may explain the absence of positive effects on nutrient digestibility. Furthermore, Pedersen and Stein[25] reported that liquid feeding at a feed-to-water ratio of 1:3 did not improve the apparent total tract digestibility of DM, GE, or P in growing-finishing pigs, which is consistent with the present results obtained under the same feed-to-water ratio. Thus, under non-fermented liquid feeding conditions, RGM supplementation appears to have limited impact on nutrient utilization.

Dietary supplementation with red ginseng marc altered hindgut fermentation patterns, as reflected by changes in fecal SCFA concentrations. No significant differences were observed during the early growing phase, suggesting that dietary treatment had little effect on hindgut fermentation at this stage. At 9 weeks, acetate and butyrate increased with increasing dietary RGM levels, indicating that moderate inclusion of RGM may provide fermentable substrates for microbial activity. Dietary fiber is known to influence SCFA production depending on its physicochemical properties and fermentability[26], and ginseng-derived polysaccharides have also been reported to modulate intestinal fermentation[27,28]. However, this response did not persist during the late finishing phase. During the late finishing period, acetate and propionate decreased, and butyrate was lowest in pigs fed 6% RGM, suggesting that excessive inclusion may have negative effects on fermentation efficiency under prolonged feeding conditions. Because butyrate is particularly important for intestinal epithelial function and barrier integrity[29], the reduced butyrate concentration in the 6% treatment may reflect a less favorable fermentation profile. These changes in hindgut fermentation coincided with reduced feed intake and poorer growth performance at the highest inclusion level. Therefore, under liquid feeding conditions, inclusion of non-fermented RGM 2% or 3% may transiently support fermentation, whereas excessive inclusion up to 6% appears to disrupt finishing phase fermentation.

In the present study, dietary RGM supplementation influenced several blood biochemical parameters; however, these changes remained within normal physiological ranges and did not indicate adverse health effects. Although ALT increased with increasing RGM levels, the value remained within the normal range (ALT: 26.0-72.1U/L) for pigs[30]. Serum BUN decreased with increasing RGM inclusion, which is more likely associated with reduced feed intake and slightly lower crude protein intake in the experimental diets. Similarly, the reduction in total cholesterol observed during the late finishing phase may be attributable to decreased energy intake, as lower feed consumption would limit substrate availability for lipid synthesis and deposition[31,32]. In contrast, the increase in serum glucose during the finishing phase remains difficult to interpret. However, serum glucose is a dynamic parameter influenced by feeding program, feeding frequency, and postprandial status in pigs[33], and may reflect variations in feeding behavior under liquid feeding conditions.

In the present study, all pork samples were obtained from pigs slaughtered at a similar body weight (110 kg), thereby minimizing the influence of slaughter weight on meat composition and physicochemical traits. Dietary RGM supplementation did not adversely affect meat quality. Previous studies have reported limited effects of red ginseng or its by-products on meat composition. Park et al.[34] found that 2.5% ginseng by-product did not alter the proximate composition of pork in finishing pigs, although ginsenoside content increased and TBARS values decreased. Similarly, Kim et al. (2014) reported that red ginseng marc supplementation at 1%, 2%, and 3% did not affect the proximate composition of broiler meat but reduced TBARS and improved shelf life, likely due to the antioxidant properties of ginsenosides. In contrast, Zhang et al.[23] observed reduced drip loss with low-level inclusion of fermented red ginseng (0.1%) or red ginseng extract (0.1%), without effects on WHC or TBARS. In the present study, ginsenoside deposition in muscle was not determined. Moreover, the unchanged TBARS values suggest that RGM supplementation did not enhance the antioxidant stability of meat.

No significant differences in pH or meat color were observed among treatments, indicating that RGM supplementation had minimal influence on postmortem muscle metabolism. Meat color is influenced by myoglobin status, muscle structure, and light scattering, while pH affects protein denaturation and water-holding capacity[35]. Kim et al.[36] reported that ultimate pH is associated with L*, a*, and b* values as well as muscle composition. In the present study, the proximate composition of pork was also unchanged, which may partly explain the stable pH and color values.

5. Conclusions

Inclusion of non-fermented red ginseng marc at 2% or 3% did not impair growth performance under the present commercial liquid feeding conditions. In contrast, 6% supplementation reduced feed intake and growth performance during the finishing period.

Liquid feeding is widely used in modern pig production and offers potential advantages in feed utilization and production efficiency. The integration of fermentation techniques with liquid feeding may further improve the utilization of by-products such as red ginseng marc by enhancing palatability and digestibility. Further research is warranted to optimize fermentation conditions and to better understand their effects on nutrient utilization and gut function in pigs.