Influence of Combination of Two Plant Extracts and Liquid Minerals Supplementation in Drinking Water on Growth Performance and Meat Quality in Pigs

A growing human population has resulted an annual increase in the global production and consumption of meat. In Korea, pork is the most consumed meat, followed by chicken, beef and mutton (Choe et al., 2015). Modern commercial farming plays an important role to meet the protein requirements, but they also have detrimental effects on the environment and public health. It is generally believed that antibiotic resistance in animals and humans is due to the excessive use of antibiotics in animal production (Suresh et al., 2017). With an increase in consumption of pork, the consumer interest in healthy foods is also increasing. There is a huge demand of high quality and safe meat without synthetic antioxidants, chemicals and antibiotic residues. Feed additives such as plant extracts are reported to improve the nutritional profile and oxidative stability of pork (Upadhaya and Kim, 2017). There is a growing interest in the use of phytogenic feed additives due to their beneficial effects, such as stimulation of feed intake, improved productivity, antimicrobial activity and antioxidant properties (Windisch et al., 2008).

Mentha arvensis is a small perennial herb, commonly called ‘Pakha’ in Korea. M. arvensis yields 90% mint oil and possesses anti-oxidant, anti-inflammatory, anti-allergic, hepatoprotective and antimicrobial effects (Biswas et al., 2014). Geranium thunbergii is commonly known as ‘Hyeoncho’ in Korea and has traditionally been used for treating diarrhoea and intestinal inflammation. It is rich in polyphenolic compounds and geraniin is the main polyphenolic compound which is responsible for the pharmacological and antioxidant activities (Yang et al., 2010).

Minerals are inorganic elements that constitute a small part of the pig’s dietary requirement. Although minerals are present in negligible amount as compared to other feed nutrients, they are important for the health and well-being of animals. Modern commercial pig farming triggers different negative impacts on the physiological, microbiological and immunity status of pigs (Debski, 2016). Besides solid form, liquids are more readily absorbed through the pig’s gut wall and there is also reduction in mineral losses (Brooks et al., 2001). Hence, administration of minerals in liquid form can be a better alternative for effective mineral absorption.

In this study, pig diets were supplemented with plant extracts and liquid minerals in drinking water to determine if the different combinations have positive impact the growth performance, carcass grading, color coordination, cooking loss, water holding capacity, pH and microbial count of swine meat.

The experimental protocols were in accordance with guidelines of the Institutional Animal Care and Use Committee at Sunchon National University, South Korea. A total of 80 crossbred (Landrace x Yorkshire x Duroc) pigs were reared for 3 months. Pigs were randomly allocated into four dietary treatments groups (20 pigs /group), each with 4 replicates (5 pigs per replicate). The dietary treatments were: control (0% plant extracts, 0% LM) and supplemented groups comprising 0.1% LM and varying ratios of plant extracts T1 (0.1% LM + 0.1% 1 MA: 4 GT), T2 (0.1% LM + 0.1% 4 MA:1 GT) and T3 (0.1% LM + 0.1 % 1 MA:1 GT).

Plant extracts of MA and GT, were collected from EFC Korea. Both plants were extracted separately using 2 kg of raw materials with the addition of 38 L of water and collected at 95°C for 2 hours, after which they were filtered through a 55 µm bag filter. The LM used in the experiment was provided by the Korea Food Ingredients Association (Table 1). The LM and plant extracts were thoroughly mixed with water and uniformly fed to the animals. The diet used in the experiment was formulated to meet the nutrient requirements recommended by NRC (1994) (Table 2).



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All pigs were weighed individually at the start of the experiment and at the end of the experiment. The amount of feed intake was calculated by subtracting the remaining amount from the feed offered. At the end, pigs were slaughtered and live weight at slaughter and carcass weight was recorded. The back fat thickness was measured at the tenth rib (using A-mode ultrasound). To determine the meat quality, the Longissimus thoracic muscle (LTM) from carcasses (three pigs per treatment) were removed at the last lumbar vertebra.

The color was measured with the help of a Chroma meter (Model CR-410 Konika Minolta sensing) with illuminant C and expressed as CIE L*a*b* units (The international Commission of Illumination (CIE) of lightness (L*), redness (a*) and yellowness (b*). The pH of the meat samples was measured using a digital pH meter (Docu-pH+ meter, Sartorius) by blending 1 g of meat with 9 ml of distilled water. Shear force values were calculated using the Warner-Bratzler shear blade set (Lloyd Instruments Ltd). Cooking loss and WHC were determined by following the procedure explained by Bostami et al., (2018).

About 25 g of meat samples were examined for microorganisms. Dilutions were prepared according to the recommendation of the International Organization for Standardization (ISO, 1995). For microbial enumeration, 20 µl sample from each serial dilution was transferred with the help of sterilized micro-pipette and spread onto Tryptic soy agar plates. For each dilution, duplicate plates were incubated at 37°C for 48 h and colonies were counted immediately. After counting, the microbial number was calculated as follows: multiplied value = no. of colonies × 10n × (100/20); where n=dilution value. Log of the multiplied value was then determined and the calculated log value of microbial count was expressed as log10CFU/g.

Statistical analyses were conducted with General Linear Models (GLM) using the SAS Statistical Package Program 9.0 (SAS, 2005). Duncan’s multiple range test was used to examine differences among treatments. The probability level of P<0.05 was considered as significant.

Growth Performance and Carcass Characteristics
 
The growth performance and carcass characteristics are presented in Table 3.

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Improvement in the weight gain could be due to the phytogenic additives that stimulate the digestive enzyme activities by increasing the output of digestive enzymes (Windisch et al., 2008). Various experimental trials reported beneficial effects of plant extracts in swine and poultry. Zhang et al., (2012) reported that 0.2% phytoncide improved the Gain: Feed (G:F) ratio and Hong et al., (2004) also demonstrated significant improvement in the average daily gain (ADG) of pigs fed 2 or 3% plant extracts. Similar to these findings, our study demonstrated significant weight gain in T3 during the experimental period. It is apparent that the higher weight gain was attributable to modulation of feed utilization through plant extracts supplementation, which was more evident during the late finishing phase. The role of minerals on the growth performance of pigs during finishing and late finishing period was unclear. Several scientists reported that production traits (ADG and feed efficiency) were decreased by lowering or deleting dietary vitamin-mineral premix during the finishing period (Choi et al., 2001; Chae et al., 2000). However, in the present study, it was found that the supplementation of pigs with MA and GT extracts improved the weight gain and FCR.

In the current study, dietary supplementation with liquid minerals and plant extracts had no effect on carcass weight and backfat thickness. These results were in agreement with Korniewicz et al., (2007) who reported no effect on carcass characteristics in pigs fed diet containing different plant extracts. While evaluating pig carcass properties, Kim and Kim (2017) found a positive correlation between carcass weight and backfat thickness, which was also found in our study (although non-significant).
 
Meat Color and Ph
 
In our study, the combination of plant extracts and liquid minerals significantly (P<0.05) decreases the L* values in the T1 and T3 groups, whereas the a* values were increased in the T3 group (Table 4). The pH values of swine meat did not differ (P>0.05) between the dietary treatments (Fig 1).

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While evaluating the sensory perception of meat color by consumers, Pastorelli et al., (2016) found that consumers mostly consider bright red color as fresh meat and hence the redness values are important for information regarding the sensory perception. The combination of plant extracts and liquid minerals in T3 significantly (P<0.05) increased the a* values of meat, suggesting an increased acceptance by the consumers. The increased redness value could be due to the retardation of lipid oxidation by natural antioxidants which are present in plant extracts. Previously, positive influences of plant extracts and minerals in swine and poultry diets was reported by different scientists (Dzinic et al., 2015; Kumar et al., 2015). In the present study, T1 and T3 reduced the L* value of meat, which is associated with low occurrence of PSE in these treatments. Several minerals are also reported to inhibit stress-induced glycolysis and the rapid decline in the pH of meat, thus improving meat quality and PSE meat defects (Apple et al., 2000). No difference was observed in the b* values of pig meat, which is in agreement with of Ao et al., (2011), who reported that Saururus chinensis extract had no effect on yellowness values in finishing pigs. In addition, Choi et al., (2001) also reported that removing minerals from the diet had no effect on meat color in pigs.
 
Although no statistically significant difference was observed in this study, the pH was lower (P>0.05) after 3 weeks of storage in all treatment groups, as compared with the control. This could be explained by the antimicrobial activity of polyphenols and metabolites present in MA and GT, which controls the microbial spoilage of meat in stored meat by reducing the bacterial growth. The polyphenols which were present in plant extracts, especially phenolic acids, flavonoids and tannins, may be responsible for maintaining constant pH of meat in experimental groups during storage, since they have the ability to regulate carbohydrate metabolism, including glycolysis (Mocanu et al., 2015).
 
Meat Shear Force, Cooking Loss and Water Holding Capacity
 
Table 4 shows that cooking loss and shear force were significantly reduced (P<0.05) in T3, while there was no difference in the WHC (P>0.05).

In the present study, T2 significantly reduced the cooking loss, indicating better retention of nutrients and tenderness of meat. However, the WHC remained non-significant in our experiment, which was consistent with the findings of Peeters et al., (2006), who reported no effect on WHC in LTM after supplementing Mg and herbs in the diet of pigs. Furthermore, studies applying herbal products and minerals in relation to meat quality are not clearly reported. This was explained by Koch et al., (1982) to be due to the meat qualities being mainly dependent on stress (handling and transport) before slaughtering, chilling regime of meat, cooking conditions and ageing time. Overall, our findings indicate no significant impact on WHC.
 
Microbial Count of Meat
 
The results of microbial counts are presented in Fig 1. The microbial count is significantly reduced (P<0.05) after slaughtering (0-week) in all treatments. After 1, 2 and 3 week of storage, no significant differences observed (P>0.05).

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Plant extracts possess broad spectrum of antimicrobial activities against gram-positive and negative bacteria. Due to the presence of numerous chemical components in plants, several mode of actions are involved in antibacterial effects (Calsamiglia et al., 2007). In the current study, reduction in the microbial count at 0 week of storage was due to presence of various active compounds in MA and GT extracts. Biswas et al., (2014) reported that the ethanolic calyx extract of MA exerts significant anti-microbial properties and Kim et al., (2010) found highest Gallic acid content in GT among 20 plants investigated. Furthermore, there is evidence showing the beneficial effect of plant extracts on the microbial load of total viable bacteria in the carcass of poultry due to the feeding of oregano essential oils (Aksit et al., 2006). Nevertheless, we failed to find significant beneficial effects on the meat microbiological count after storage. We hypothesize this may be due to the low level of supplementation to effectively influence bacterial activity. These results are in agreement with a previous study in which 1 or 2 g/kg S. chinensis extract had no effect on the oxidative stability in pork (Ao et al., 2011).

It may be concluded that the combination of plant extracts and liquid minerals in T2 could be ideal for antibiotic and synthetic antioxidant free meat and exert beneficial impact on the growth and meat quality of crossbred pigs. Further research is required for determining the optimal proportion of the combinations for industrial applications and better storage characteristics.

This research was supported by the Ministry of Trade, Industry & Energy (MOTIE), Korea Institute for Advancement of Technology (KIAT) through the Encouragement Program for the Industries of Economic Cooperation Region.