Effects of dietary supplementation of Quillaja saponin on growth performance, nutrient digestibility, fecal gas emissions, and meat quality in finishing pigs

ABSTRACT

We evaluated the effects of Quillaja saponin (400 mg/kg) on growth performance, nutrient digestibility, fecal gas emissions, and meat quality in pigs when used as a supplement in a finishing pig diet. In total, 80 finishing pigs [(Yorkshire × Landrace) × Duroc] with an average initial body weight of 61.53 ± 4.41 kg were used in a 61-day study. Pigs were allotted to one of two treatments according to initial body weight with 10 replicate pens per treatment and four pigs (two barrows and two gilts) per pen. The dietary treatments consisted of (1) a basal diet (CON), or (2) a CON + 400 mg/kg Quillaja saponin (QS) diet. The growth performance and nutrient digestibility were not affected by supplementing the diet with QS. The ammonia emissions were decreased by Quillaja saponin supplementation (P < 0.05). Pigs consuming the QS diet had a higher meat water-holding capacity (WHC) (P < 0.05) and a lower meat drip loss on day 7 (P < 0.05) compared to pigs consuming the CON diet. Our results indicate that a diet supplemented with 400 mg/kg Quillaja saponin can improve the meat WHC and drip loss, and reduced fecal ammonia emission.

KEYWORDS:

• Quillaja saponin
• finishing pigs
• triterpenoid saponins
• meat quality
• fecal gas emission

Introduction

Triterpenoid saponins are surface-active glycosides of triterpenes, which are naturally occurring compound in a variety of plants and fruits. They have a wide range of biological activities that have attracted human interest from ancient times. The biological and pharmacological activities of triterpenoid saponins such as anti-fungal (Chludil et al. 2002), anti-inflammatory (Sarkhel 2016), anti-microbial (Kaczorek et al. 2016), anti-viral (Chen 2014), anti-oxidant (Chaudhary et al. 2018), and immunomodulating activities (Chaudhary 2017) and cardioprotective (Li et al. 2014) and hepatoprotective effects (Wang et al. 2014) have been reported. In animal husbandry, triterpenoid saponins have been reported to improve production, immunity, gut health, and meat quality of monogastric animals without affecting production cost (Chaudhary et al. 2018).

Quillaja saponin, which is derived from the soap bark (Quillaja saponaria Molina) tree, contains a triterpenoid (non-steroidal) sapogenin structural component (Francis et al. 2002). Quillaja saponin exhibits a variety of effects when used as a feed additive. Positive effects on feed consumption and feed conversion efficiency were observed in weaned pigs fed 125 mg/kg Quillaja saponin supplemented to the basal diet (Vaclavkova and Beckova 2008). Ilsley et al. (2003) reported that supplementing a diet with 250 mg/kg Quillaja saponin increased dry matter and crude protein digestibility of the sows. According to Hu et al. (2006) and Wang et al. (2017), triterpenoid saponins may inhibit growth performance at high doses and promote growth performance at low doses. Indeed, Ilsley et al. (2005) noted that a diet containing 750 mg/kg Quillaja saponin did not affect the growth performance of pigs but feeding the pigs with a diet supplemented with 1300 mg/kg Quillaja saponin negatively affected their growth performance. Turner et al. (2000) reported that weaned pigs fed a diet supplemented with 453.59 mg/kg (16 oz/ton) Quillaja saponin did not affect the growth performance. Therefore, the adequate dose of Quillaja saponin promoting growth is probably between 125 and 450 mg/kg. However, the beneficial effects of Quillaja saponin as a dietary supplement in finishing pigs have not been investigated yet.

Therefore, the objective of this experiment was to test the hypothesis that a diet supplemented with 400 mg/kg Quillaja saponin would exert positive effects on the growth performance, nutrient digestibility, meat quality, and emission of fecal noxious gases in finishing pigs.

Materials and methods

The experimental protocols for the management and care of animals were reviewed and approved by the Animal Care and Use Committee of Dankook University, Yongin, South Korea.

Quillaja saponin dietary supplement

The Quillaja saponin (Delacon Inc., Steyregg, Austria) used in this study was a commercial product supplied as a Quillaja saponin-enriched biomass powder (99% content) prepared from the Q. saponaria Molina tree from the Andes region of Chile.

Animals, housing, and treatments

A total of 80 crossbred finishing pigs [(Yorkshire × Landrace) × Duroc] with an initial average body weight (BW) of 61.53 ± 4.41 kg were used in a 61-day experiment. Pigs were allotted according to initial BW to one of two treatments in a complete randomized block design. The treatments were consisted of 10 replicate pens with four pigs (two barrows and two gilts) per pen. The dietary treatments were (1) a basal diet (CON) and (2) CON + 400 mg/kg Quillaja saponin (QS) diet. The diets were formulated to meet the nutrient requirements recommended by the National Research Council (NRC 2012) (Table 1). All pigs were housed in an environmentally controlled facility with a slatted plastic floor. The ambient environmental temperature within the house was thermostatically controlled at 25°C throughout the experiment. Each pen was equipped with a one-sided self-feeder and a nipple drinker to allow pigs to take feed and water ad libitum.

Table 1. Composition of the experimental finishing pig diets (as-feed basis).

Items
Ingredients (%)
Yellow corn	53.39
Wheat	15.00
Soybean meal (Crude protein 44%)	14.30
Soybean meal (Crude protein 45.4%)	6.64
Limestone	0.84
Salt	0.30
Dicalcium phosphate	1.30
Methionine (50%)	0.06
L-Lysine H2SO4 (51%)	0.45
L-Threonine (98.5%)	0.15
Vitamin premix^a	0.05
Mineral premix^b	0.12
Animal fat	4.25
Choline (50%)	0.15
Molasses	3.00
Total	100.00
Calculated value
Available phosphorus, %	0.28
Digestible energy (kcal kg^−1)	3560
Analyzed composition, %
Dry matter	87.35
Moisture	12.65
Crude protein	15.55
Crude fat	6.69
Total calcium	0.72
Total phosphorus	0.54
Lysine	0.90
Methionine	0.26

^aProvided per kilogram of complete diet: 4,000 IU vitamin A; 800 IU vitamin D₃; 171 IU vitamin E; 2 mg vitaminK₃; 4 mg riboflavin; 20 mg niacin; 4 mg thiamine; 11 mg d-pantothenic acid; 166 mg choline; 0.08 mg biotin; 16 μg vitamin B₁₂.

^bProvided per kilogram of complete diet: 15 mg Cu (as CuSO₄·5H₂O); 80 mg Fe (as FeSO₄·7H₂O); 56 mg Zn (as ZnSO₄); 73 mg Mn (MnO₂); 0.3 mg I (as KI); 0.5 mg Co (as CoSO₄·5H₂O); 0.4 mg Se (as Na₂SeO₃·5H₂O).

Sampling and measurements

The feed intake of each pen was recorded on a daily basis. The body weight (BW) of individual pigs was measured at the beginning and the end of the experimental period. The feed consumption and BW were used to calculate the average daily gain (ADG), average daily feed intake (ADFI), and feed conversion ratio (FCR).

On day 55 of the experiment, the diets were supplemented with 0.20% chromium oxide (Cr₂O₃) as an indigestible marker to estimate the apparent total tract digestibility (ATTD) of dry matter (DM), nitrogen (N), and gross energy (GE). After mixing with Cr₂O₃, representative feed samples were collected and stored for further analyses. On day 61 of the experiment, two pigs per pen were randomly chosen for the collection of fecal samples by the rectal massage method. Fecal samples from the same pen were pooled and mixed immediately. All feed and fecal samples were stored at –20°C until further analysis. For chemical analysis, samples were dried at 60°C for 72 h and then ground to pass through a 1-mm sieve. Feed and fecal samples were analyzed for DM (method 930.15) and N (method 984.13) using the AOAC international (2007) method. A bomb calorimeter (Parr 6100; Parr Instrument Co., Moline, IL, USA) was used to measure the heat of combustion of samples to determine the GE. Chromium levels were determined using a UV absorption spectrophotometer (UV-1201; Shimadzu, Kyoto, Japan). The ATTD was calculated using the following formula: ATTD (%) = [1 − {(Nf × Cd) ∕ (Nd × Cf)}] × 100, where Nf is the nutrient concentration in the feces (% DM), Nd is the nutrient concentration in the diet (% DM), Cd is the chromium concentration in the diet (% DM), and Cf is the chromium concentration in the feces (% DM).

On day 59 of the experiment, two pigs per pen were randomly selected for the collection of fresh fecal samples via the rectal massage method to determine the concentrations of fecal ammonia (NH₃), total mercaptans (R–SH), and hydrogen sulfide (H₂S). Samples from the same pen were mixed and stored in 2.6-L plastic boxes in duplicate. Each box had a small hole in the middle of one side sealed with an adhesive plaster, and the fecal samples were allowed to ferment for 24 h at room temperature (25°C). Before measurement, fecal samples were homogenized by manual shaking for 30 s. Air samples (100 mL) were taken from the head-space above the surface of the excreta through the small hole; the sampling height was approximately 2.0 cm. Two samples from each pen were measured and the average was calculated. Gas was sampled and analyzed using a gas-sampling pump (GV-100S; Gastec Corp., Japan; Gastec detector tube No. 3La for NH₃; No. 4LK for H₂S; No. 70L for R–SH).

At the end of the experiment, all pigs were euthanized at a local commercial slaughterhouse, and the carcasses were chilled at 2°C for 24 h. Subsequently, one pig from each pen was randomly selected and a sample of the right loin was removed between the 10th and 11th ribs. Sensory evaluation (colour, marbling, and firmness score) was immediately conducted at ambient temperature according to the National Pork Producers Council Standards (NPPC 2000). After the subjective evaluation, lightness (L*), redness (a*), and yellowness (b*) values at three locations on each sample surface were measured using a CR-410 Chroma Meter (Konica Minolta Sensing, Inc., Osaka, Japan). At the same time, the pH values of each sample were measured at two different locations using a pH metre (Pittsburgh, PA, USA), and the average was recorded. Subsequently, 0.3 g of meat sample was pressed at 3000 psi for 3 min on a 125-mm diameter piece of filter paper to determine the water-holding capacity (WHC). The areas of the pressed sample and the expressed moisture were delineated and then determined using a digitizing area-line sensor (MT-10S; M.T. Precision Co. Ltd., Tokyo, Japan). The ratio of water area to meat area was calculated and presented as the WHC. Simultaneously, the aforementioned digitizing area-line sensor was used to measure the longissimus muscle surface of the 10th rib to determine the longissimus muscle area (LMA). To determine cooking loss, 5 g of meat sample was heat-treated in a plastic bag in a water bath (100°C) for 5 min and then allowed to cool at room temperature (25°C). Cooking loss was calculated as: [(sample weight before cooking − sample weight after cooking) / sample weight before cooking] × 100. Meat samples of approximately 2 g were each suspended by a fishhook, surrounded with an inflated plastic bag, and stored in a 4°C environment. The weights of the samples were recalculated during days 1, 3, 5, and 6 to determine the drip loss.

Statistical analysis

All data were statistically analyzed using the Student's t-test in SAS software (SAS version 9.4, 2014, Inst. Inc., Cary, NC, USA). The pen served as the experimental unit. The data are presented as the means ± standard deviation. Values of P < 0.05 were taken to denote statistical significance.

Result and discussion

The results of supplementing the diet of pigs with 400 mg/kg Quillaja saponin on growth performance showed that the growth performance was not significantly different among the treatment diet groups (Table 2). Similar results were reported by Turner et al. (2002), who demonstrated that feeding weaned pigs with a diet supplemented with 500 mg/kg Quillaja saponin did not affect the ADG, ADFI, and FCR. Turner et al. (2000) noted that feeding the weaned pigs with the diet supplemented 453.59 mg/kg (16 oz/ton) Quillaja saponin did not affect their growth performance. Kang et al. (2010) observed that supplementing the diet of weaned pigs with 500 mg/kg triterpenoid saponin (Acantbepanax senticosus saponin) did not affect the ADG, ADFI, and FCR. Conversely, Bartoš et al. (2016) demonstrated that growing-finishing pigs (mean BW, 45.4 ± 2.5 kg) fed a diet supplemented with 100 or 150 mg/kg phytogenic feed additive, containing Quillaja saponin and other substances, exhibited significantly improved ADG and ADFI, but the FCR was unaffected. Vaclavkova and Beckova (2008) noted that weaned pigs fed a diet supplemented with 125 mg/kg Quillaja saponin had higher feed consumption and feed conversion efficiency. Nevertheless, studies on the effect of Quillaja saponin on growth performance of finishing pigs are not reported. The results of our study confirmed that supplementing the diet of pigs with Quillaja saponin at a concentration of 400 mg/kg could not enhance the growth in finishing pigs. The DM and N digestibility and GE retention were also not affected by dietary addition of Quillaja saponin in this study (Table 2). Since nutrient digestibility is highly correlated with growth performance (Cai et al. 2018), the lack of improvement in the digestibility of nutrients with QS supplementation in the present study led to an insignificant effect on growth performance.

Table 2. Effect of Quillaja saponin on growth performance and nutrient digestibility in finishing pigs.

	Quillaja saponin, mg/kg
Items	0	400	P-value
Body weight, kg
Initial	61.53 ± 2.62	61.52 ± 2.62	0.99
Finish	104.60 ± 3.22	106.00 ± 3.06	0.34
ADG, g	705.50 ± 32.62	728.50 ± 23.59	0.09
ADFI, g	2209.10 ± 126.60	2263.50 ± 98.17	0.30
FCR	3.13 ± 0.08	3.11 ± 0.07	0.49
Apparent total tract digestibility, %
DM	72.28 ± 2.82	73.48 ± 2.52	0.39
GE	72.57 ± 1.96	73.91 ± 2.86	0.29
N	71.90 ± 2.60	72.82 ± 1.90	0.43

Results were presented as mean ± standard deviation.

Abbreviation: ADG, average daily gain; ADFI, average daily feed intake; FCR, feed conversion ratio; DM, dry matter; N, nitrogen; GE, gross energy; SEM, standard error of the mean.

The effects of Quillaja saponin supplementation on the emission of fecal noxious gases in pigs are shown in Table 3. The concentration of NH₃ was lower in the fecal sample of pigs fed the diet containing QS compared to the pigs fed the CON diet (P < 0.05); however, the QS containing diet had no significant effects on the concentrations of fecal H₂S or R–SH. Bartoš et al. (2016) also demonstrated that growing-finishing pigs fed with diet containing 100 or 150 mg/kg phytogenic feed additive, which contained Quillaja saponin and other substances, emitted less NH₃ per animal per day. Due to the poor absorption characteristics of saponin (Li et al. 2013; del Hierro et al. 2018), it can have several effects in the gastrointestinal tract. NH₃ production occurs following microbial fermentation of feed protein in the intestine. Notably, saponins and proteins can form saponin-protein complexes that are difficult to be utilized (Potter et al. 1993), thereby inhibiting the microbial fermentation of protein (Killeen et al. 1998). Additionally, Quillaja saponin also has the ability to bind NH₃ (Brogna 2012) and may bind NH₃ that has already been produced in the intestine. In addition, the enhancement of nutrient digestibility reduces the substrate for microbial fermentation in the gut thereby diminishing the excreta noxious gas emission (Yan et al. 2011). However, DM and N digestibility and GE retention were unaffected by the QS diet. Thus, the significant decrease in NH₃ observed in this study may be due to the ability of Quillaja saponin to form saponin-protein complexes and its ability to bind NH₃. Further experiments should therefore be conducted to determine the effects of Quillaja saponin supplementation on intestinal microbiota community in finishing pigs, because this may reveal the effect of saponin-protein complexes formation on the microbial fermentation of protein.

Table 3. Effect of Quillaja saponin on fecal gas emission in finishing pigs.

	Quillaja saponin, mg/kg
Items, ppm	0	400	P-value
R–SH	5.10 ± 1.52	4.83 ± 0.67	0.75
H2S	6.53 ± 0.61	5.70 ± 1.27	0.29
NH3	7.28 ± 0.28	6.58 ± 0.31	0.02

Results were presented as mean ± standard deviation.

Abbreviation: NH₃, Ammonia; H₂S, hydrogen sulfide; R–SH, total mercaptans; SEM, standard error of the mean.

The WHC is an important indicator of meat quality. As shown in Table 4, dietary addition of 400 mg/kg Quillaja saponin increased the WHC (P < 0.05) and decreased the drip loss on day 7 (P < 0.05), but no effects were observed on other indices of meat quality such as sensory parameters (colour, marbling, firmness), meat colour (lightness, redness, yellowness), pH, cooking loss, or LMA. Myofibrils, which consist of myosin and actin, are the compositional unit of the physical structure of muscle. Myosin and actin together are known as myofibrin. In addition, muscle contains some adipose tissue. The oxidation of fat generates free radicals (Nigam and Schewe 2000), which promote the oxidation of myofibrin and reduce the WHC of muscle (Liu et al. 2010). As reported by Ibrahim et al. (2010) and Bera et al. (2019), lipid oxidative stability was preserved by triterpenoid saponin in broiler or lamb meat. Moreover, Quillaja saponin has been shown by Tippel et al. (2017) to exhibit high antioxidant activity. As the results reported by Zdanowska-Sąsiadek et al. (2019), animals fed with feed containing antioxidant substances ameliorated meat WHC and drip loss. Therefore, the level of meat oxidation may be reduced in pigs that consumed 400 mg/kg Quillaja saponin, thereby contributing to an enhanced meat WHC and a reduced meat drip loss. Increased WHC reduces the weight loss of pork due to drip loss, which reduces the economic losses of retailers. The reduction in drip loss also limits the amount of water present in the packaging bag during sale and storage, which improves the acceptability of the meat to consumers (Ngapo et al. 2007).

Table 4. Effect of Quillaja saponin on meat quality in finishing pigs.

	Quillaja saponin, mg/kg
Items	0	400	P-value
Meat colour
L*	46.75 ± 4.52	47.66 ± 0.68	0.72
a*	14.10 ± 0.59	14.18 ± 0.48	0.83
b*	3.87 ± 0.47	3.94 ± 0.11	0.79
Sensory evaluation
Colour	3.33 ± 0.06	3.31 ± 0.07	0.66
Firmness	3.00 ± 0.32	2.89 ± 0.15	0.56
Marbling	3.06 ± 0.16	3.13 ± 0.18	0.62
Cooking loss, %	32.63 ± 1.77	30.78 ± 2.26	0.24
Drip loss, %
d1	6.28 ± 0.91	6.11 ± 1.46	0.85
d3	13.00 ± 0.54	11.69 ± 1.58	0.17
d5	18.40 ± 1.61	17.24 ± 1.35	0.31
d7	23.70 ± 1.06	21.19 ± 1.03	0.01
pH	5.49 ± 0.12	5.51 ± 0.15	0.88
LMA, cm^2	60.63 ± 3.07	61.90 ± 2.98	0.57
WHC, %	44.15 ± 1.85	48.72 ± 0.54	0.01

Results were presented as mean ± standard deviation.

Abbreviation: WHC, water-holding capacity; LMA, longissimus muscle area; SEM, standard error of the mean.

Conclusions

Based on our results, supplementing a finishing-pig diet with 400 mg/kg Quillaja saponin can contribute to the reduction of ammonia emission which is one of the environmental pollutants. In addition, it can enhance meat water-holding capacity and reduce the meat drip loss. The improved meat water-holding capacity and drip loss may increase product value. However, 400 mg/kg Quillaja saponin was not found to be potential in promoting the growth of finishing pigs. More experiments are needed to assess the effects of Quillaja saponin in finishing pigs.

Disclosure statement

No potential conflict of interest was reported by the author(s).