Long-term storage of animal feed in high humidity and high temperature condition is a major problem of livestock farm production and management, because nutrients in feed can be decomposed by harmful microorganisms. For example, Aspergillus and other fungi may produce toxins such as aflatoxins, while pathogenic bacteria, such as Salmonella enteritidis and Escherichia coli, present in feed or feedstuffs for animal consumption. All of these can be dangerous for animal health (Cole and Cox, 1981). The diet of pig consists mainly of cereal grains, which often easily contaminated with aflatoxin-producing molds. It is reported that pigs to be one of the most sensitive animals to the effects of aflatoxin (Shi et al., 2005). Thus, aflatoxin-contaminated feed is a serious threat to the swine industry.

Phytoncide are natural volatile compounds emitted by trees and plants as a protective mechanism against harmful insects, animals, and microorganisms. Trees and plants synthesize phytoncide as secondary metabolites of photosynthesis. Phytoncide are enriched in terpenoids, phenylpropanoids, and alkaloids; major ingredients include monoterpenoids, including α-pinene, careen, and myrcene (Durham et al., 1994; Nose, 2000; Oikawa, 2005). As a mean of suppressing activity of microorganisms, such as bacteria and fungi, relatively large amounts of phytoncide were released by Korean pines and other conifers into the environment (Pečiulytė et al., 2010). The suppressive activity relies on essential oil, terpenoids, alkaloid, and phenylpropanoids of phytoncide (Durham et al., 1994). Due to them, phytogenic feed additive (PFA) have a potential capacity to intercalate into the bacterial membrane, disintegrate the membrane, and cause ion leakage (Burt, 2004; Hashemi and Davoodi, 2010). Moreover, this can interfere with regulatory networks of signal transduction and gene expression in aflatoxin biosynthesis, or by blocking the enzymatic activity of a biosynthetic enzyme (Holmes et al., 2008).

These previous findings suggested that phytoncide as a potential feed additive. In support of this, one study described the antioxidative potential of phytoncide and their effects in reducing oxidative stress responses in stroke-prone spontaneously hypertensive rats (Kawakami et al., 2004). Moreover, stress level was known to have negative correlation with meat quality (Terlouw, 2005). According to these previous studies, we could hypothesis that dietary phytoncide supplementation may help to improve growth performance and meat quality in finishing pigs. However, the effect of dietary phytoncide supplementation in finishing pigs has not yet been investigated. Thus, this study was conducted to determine the effect of dietary phytoncide supplementation on growing performance, blood characteristics, and meat quality in finishing pigs.

As an alternative feeding strategy to growth promoters, PFA have received considerable attentions recently. Various trials have demonstrated positive effects of PFA in swine and poultry (Wang et al., 2008; Windisch et al., 2008; Van Krimpen et al., 2010). Wang et al. (2008) reported that 0.04% dietary phytogenic feed additive, which was made of essential oils, flavonoids, pungent substances, and mucliages, did not affect the ADFI of lactating sows. Whereas, Zhang et al. (2012) observed that weaning pigs fed with 0.2% phytoncide showed a greater G:F ratio. Moreover, Yan et al. (2010) reported that 0.01% essential oil used as PFA increased ADG and G:F at different nutrient densities in pigs. Consistent with these previous studies, our study demonstrated that 0.04% phytoncide increased ADG and G:F ratio in finishing pigs. Essential oils, as a main content of phytogenic additive, may have beneficial effects such as antiviral and antimicrobial activity, and are capable of stimulating enzyme activity and immune function in livestock (Williams and Losa, 2001; Yan et al., 2010). Also, positive of essential oils on digestive system and stimulating effect on the output of digestive enzymes from the pancreas, gut mucosa, and increase bile flow have been reported (Jamroz and Kamel, 2002; Jamroz et al., 2005; Jang et al., 2007), which may explain the improvement of growth performance of pigs in our present experiment. Also, specific capabilities of phytogenic compounds is to enhance the activities of digestive enzymes (bile, pancreatic lipase and amylase etc.) and nutrient absorption (Windisch et al., 2008), which may be another explanation for our results.

The quality of plant materials, selection of particular plants, and forms for administration (i.e., extracts, oils, and dried herbs) also influence their effects on pig performance. As mentioned above, the active substances in phytoncide have a potential capacity to intercalate into the bacterial membrane, disintegrate the membrane, and cause ion leakage, it means that PFA could inhibit the biosynthesis or expression of aflatoxin, or block the enzymatic activity of a biosynthetic enzyme, which including superoxide dismutase, xanthine oxidase, glutathione peroxidase, and two microsomal reductases (Burt, 2004; Holmes et al., 2008; Hashemi and Davoodi, 2010). Those may be the reason why it could promote growth performance of pigs by protecting feed quality. However, inconsistent results have been obtained regarding the effects of PFA on ADFI in animals. Yan et al. (2011a) noted that 1 g/kg herbal extract (Houttuynia cordata or Taraxacum officinale) used as PFA increased ADFI during a 10-week trial. Wang et al. (2007) and Wenk et al. (2003) reported that herbs used as PFA could improve the flavor and palatability of feed, subsequently increasing the total feed intake and growth performance. Yan et al. (2010) demonstrated that 0.01% essential oil, including thyme, rosemary, oreganum extracts, and kaolin covered by starch had a tendency to lower ADFI. One reasonable explanation for the lower ADFI might be the tranquilizing effect of PFA, which reduced the spontaneous physical activity of the pigs. Physical activity influences heat production, which can cause additional expenditure of energy (Wang et al., 2007). Moreover, pungent substances of some plants (e.g., capsaicin, allitricin, and piperine), which are the active components of PFA, may reduce the palatability of feed and restrict their use for animal feeding purpose (Zhong et al., 2011). In line with our study, previous studies also showed dose-related depressions of palatability of pigs fed with essential oils from the herbs thyme and oregano, as well as from caraway and fennel (Jugl-Chizzola et al., 2006; Schone et al., 2006). Therefore, according to these previous studies the elevate effect of essential may depressed as pungent substances concentration increased.

Czech et al. (2009) reported that pigs fed a mixture with a supplement of 8 g/kg herbal mixture during the whole fattening period were characterized by a significantly higher value of red blood cell system indices, including serotonin, hemoglobin, and RBC. Yan et al. (2011b) confirmed this result, describing increased RBC concentrations in pigs fed 250 or 500 mg/kg of herb extract mixture. Pungent substances (e.g. garlic, black pepper, and chilli), the active components of PFA, could activate blood circulation and metabolic processes (Rodas, 2006). Consistent with that, Iranloye (2002) showed that feeding rats with 200 mg/kg garlic juice daily increased the RBC and WBC. Moreover, Wang et al. (2008) observed that RBC and WBC were increased significantly with PFA treatment. Phytoncide had also been shown to reduce stress responses by lowering stress-related hormones (Kawakami et al., 2004). Collectively, these findings indicate that phytoncide as PFA can increase blood circulation, metabolic processes, and the immune system of pigs.

Phytoncide can reduce stress responses in stroke-prone spontaneously hypertensive rats (Kawakami et al., 2004). Nam and Uhm (2008) documented that phytoncide decreased serum cortisol levels significantly in college students. Psychological stress affects immune function and predicts infectious disease susceptibility in humans and animals (Marsland et al., 2002). Plant extracts could stimulate T cell-mediated immune responses (Islam et al., 2004). Additionally, flavonoids, one bioactive substance within phytoncide, exhibit inhibitory effects against multiple viruses and improve immunity (Critchfield et al., 1996). In line with previous studies, the concentration of stress-related hormone, cortisol, was reduced significantly with phytoncide supplementation in our present study, indicating that stress was reduced and immunity was enhanced with phytoncide supplementation (Koopmans et al., 2005). In contrast, the effects of PFA on blood profiles have been inconsistent, which might be attributable to interactions between PFA and different feed formulae.

Unacceptable water-holding capacity costs the meat industry millions of dollars annually. Product weight losses due to purge can average as much as 1% to 3% in fresh retail cuts (Offer and Knight, 1988a) and can be as high at 10% in pale soft exudative products (Melody et al., 2004). In addition to the loss of salable weight, purge loss also entails the loss of a significant amount of protein (Offer and Knight, 1988b). On average, purge can contain approximately 112 mg of protein per mL of fluid, mostly water-soluble, sarcoplasmic proteins (Savage et al., 1990). In the current study, phytoncide treatments showed beneficial effects on WHC. It is clear that early postmortem events including the rate and extent of pH decline, proteolysis, and even protein oxidation, are key to influencing the ability of meat to retain moisture (Huff-Lonergan and Lonergan, 2005). Consequently, the antioxidant activities of phytoncide may be a factor causing the higher WHC. Moreover, cortisol was known to increase associated with stress, and stress would decrease meat quality (Terlouw, 2005), in line with our study, cortisol decreased and meat quality increased with 0.04% of phytoncide inclusion.

In conclusion, our results indicate that Korean pine extract supplementation can promote growth performance and elevate meat quality. So that dietary Korean pine extract, phytoncide, could be considered as a potential natural growth promoter in finishing pigs.