## 4 Discussion  
We recently reported that the nutritive value and in vitro rumen lignin digestibility of WRF-pretreated corn straw was significantly higher than untreated corn straw. In particular, CP content in WRF-pretreated corn straw increased by 40.5-68.4% and the in vitro lignin digestibility increased 40% depending on various fungi when compared with untreated corn straw [14]. In the present study, differences in metabolites between WRF-pretreated and untreated corn straw were characterized. In total, 392 metabolites were identified in Control and WRF-pretreated corn straw and these metabolites were categorized into 12 classes, including 112 dipeptides, 76 acids, 25 amines, 24 individual amino acid, 18 esters, 16 ketones, 15 alcohols, 13 adenosines, eight carbohydrates, five phenols, three aldehydes and other metabolites (Figure 1). Among all these identified metabolites, 245 metabolites were upregulated and 147 metabolites were downregulated in WRF-pretreated versus Control corn straw. The biggest difference was that more upregulated and less downregulated individual amino acids and dipeptides were detected in WRF-pretreated versus Control corn straw. In addition, esters, alcohols, ketones, amines, adenosines and carbohydrates in WRF-pretreated corn straw were upregulated more than those of Control corn straw, whereas, all downregulated categories in WRF-pretreated corn straw were less than those of un-pretreated corn straw. Based on changes in metabolite profile, nutritive value, especially AA and peptides of corn straw were optimized by WRF pretreatment. In our previous study, we reported that GIN infections decreased \(a^{\star}\) values and total heme pigment content of lamb meat due to some blood-sucking nematodes such as _Haemonchus contortus_ will result in anemia and blood iron loss; therefore, GIN infections had negative effects on meat color. Meanwhile, many studies have found that feeding plant-derived-polyphenols could alleviate such negative effects on meat by eliminating GIN infections [19; 26]. Consequently, in the present study, we hypothesized that reducing GIN burden by changing the diet would improve meat color. Some studies have attempted to improve meat quality of GIN-infected sheep by increasing dietary protein to mount a strong immunity associates to GINs. For example, feeding bananas without any additional protein resulted in infected lamb's meat with lower \(b^{\star}\) and \(L^{\star}\) value and higher \(a^{\star}\) value compared to dietary protein supplementation [27]. Furthermore, supplemental dietary protein decreased \(L^{\star}\) values and increased \(a^{\star}\) values of lamb meat [3]. Overall, dietary protein supplementation can improve meat quality of lambs infected with GINs [28]. Consistent with our hypothesis, in the present study, WRF lambs had significantly lower \(L^{\star}\) and higher \(a^{\star}\) values in the two tested muscles. There are two proposed causes. First, feeding WRF-pretreated corn straw reduced the numbers of parasitic GINs, based on lower FEC and higher PCV of WRF lambs. Various fungi, including _Ascomycota_, _Zygonycota_, _Basidiumycota_ and _Cityridionycota_, were antagonistic to nematodes and their eggs, using them as nutrition sources [10]. In addition, some chemicals have antagonistic relationships toward nematodes. For example, 2-decenedioic acid in _Pleurotus ostreatus_ (a wood-rotting Basidiomycete) was isolated as a nematicidal compound. In addition, two fatty acids, namely linoleic acid and S-coriolic acid were the nematicidal compounds formed by _Pleurotus pulmonarius_[29]. Based on the present metabolite profiles, WFR-pretreated corn straw may contain these nematicidal compounds to control GINs. Second, infection with GINs may result in a total net loss of about 12 g protein/day, which consist of a net loss of about six grams form the gastrointestinal tract and a further loss of about six grams through increased AA oxidation in the body [30].