## 2 Materials and Methods
### Analytical Procedures  
Plasma iron contents were measured using a multiparameter automated hematology analyzer (7020, Hitachi, Beijing, China) with commercial kits (Meikang Biotechnology Co., Ltd., Ningbo, China). The FEC was determined using the [PERSON]'s technique as described by [PERSON] et al. [19] with results expressed as eggs per gram (EPG) of feces. The PCV of whole blood was determined using a UNICO-hematocrit centrifuge (182-E, Dayton, NJ, UAS) and a microcapillary reader ([PERSON]/IEC Division). The pH values of the LTL and SM muscles were tested post-mortem at 24 h (pH\({}_{24}\)) using a pH meter (PHS-3C, Jiangsu Jiangfen Electroanalytical Instrument Co., Ltd., Jiangyan, China), calibrated with pH 4.6 and 7.0 buffers. Each muscle sample was tested 3 times at different locations. The LTL and SM muscle samples were cut into strips (\(\sim\)1.27 cm diameter and 20 mm long) and sheared parallel to the muscle fiber direction. At 24 h post-mortem, shear force was measured using a muscle tenderness meter (XU155, Xieli Science and Technology Co., Ltd., Qinhuangdao, China). Each sample of LTL and SM, muscles were tested 3 times and values averaged. For each muscle, meat color traits of \(L^{*}\) (lightness), \(a^{*}\) (redness) and \(b^{*}\) (yellowness) were measured with a CR410 chroma meter (Konica Minolta Sensing, Inc., Japan) calibrated with a standard white plate before measuring. Three replicates of each sample at different points were measured and the average value was used. Intermuscular fat (IMF) was determined by extracting the sample with petroleum ether using an automatic soxhlet extractor (SER148, VELP, Beijing, China) after being freeze dried for 24 h at \(-\)50 \({}^{\circ}\)C with a vacuum freezing dryer (ScanVac CoolSafeTM, LaboGene, Ltd., Lynge, Denmark). This Soxhlet extraction was operated as described by [PERSON] et al. [20]. Briefly, \(\sim\)0.3 g freeze-dried meat sample was extracted in 80 mL petroleum ether for 4 h and then the residue was heated in an oven at 105 \({}^{\circ}\)C for 30 min to remove residual petroleum ether. The AA profiles of meat were analyzed using an automatic amino acid analyzer (Hitachi L-8900, Beijing, China), as described by [PERSON] et al. [21]. Briefly, 0.1 g of dry meat sample was placed in a hydrolysis tube containing 10 mL of hydrochloric acid (6 M), 4 drops of phenol solution added, frozen at \(-\)20 \({}^{\circ}\)C for 3 min, evacuated for 5 min, nitrogen added, hydrolyzed for 22 h and then cooled to roomtemperature. Hydrolysate was filtered in a constant volume of 50 mL and 1.0 mL of the filtrate dried in vacuo to dissolve 1.0 mL of ammonium citrate buffer and pass through a 0.22-\(\upmu\)m filter membrane. Ion exchange chromatography column (855-3294, Hitachi, Beijing, China), where the amino acids were eluted by the sodium buffer system. After reaction with ninhydrin, the synthesized derivatives were simultaneously measured at wavelengths of 440 and 570 nm. Due to the low response at 570 nm, the proline derivative was detected at 440 nm. The volatile flavor compounds in the meat sample were measured using Headspace solid phase micro-extraction (SPME) coupled with gas chromatography-mass spectrometry (GC-MS) as described by [PERSON] et al. [22] with minor modifications by our lab. Briefly, SPME with 65 \(\upmu\)m PDMS/DVB fiber (Supelco, Bellefonte, PA, USA) was used to extract volatiles from 2-g samples at 70 \({}^{\circ}\)C for 30 min. After absorption, the fiber was stuck to a GCMS-QP2010 gas chromatograph mass spectrometer (Shimadzu, Tokyo, Japan) at 250 \({}^{\circ}\)C for 4 min during desorption. The carrier gas was helium and the flow rate was 1.4 mL/min. HP-5 MS column (0.25 mm internal diameter, 30 m length, 0.25 \(\upmu\)m film thickness, Shimadzu), oven temperature was operated for 5 min at 40 \({}^{\circ}\)C, increased to 230 \({}^{\circ}\)C at 3 \({}^{\circ}\)C/min for 5 min, was used to separate volatile compounds with a total acquisition program of 73 min.