## 2 Materials and Methods
### Volatile Compound Analysis  
The extraction, separation, identification and determination of volatile compounds were carried out following the procedure and conditions first described by [PERSON] et al. [22]. Shortly, solid-phase microextraction (SPME) with an autosampler Pal RTC-120 was employed for the separation of volatile compounds, while a gas chromatograph 7890B GC-System (Agilent Technologies, Santa Clara, CA, USA) coupled to a mass selective detector 5977B MSD (Agilent Technologies) was used for their separation, identification and quantification.  
In particular, the SPME tool was loaded with a fused-silica fiber (10 mm length) coated with a 50/30 mm thickness of DVB/CAR/PDMS (divinylbenzene/carboxen/polydimethylsiloxane) (Supelco, Bellefonte, PA, USA). Prior to analysis, fiber was conditioned by heating in a SPME Fiber Conditioning Station at 270 \({}^{\circ}\)C for 30 min. Meanwhile, 1 \(\pm\) 0.02 g of minced meat was weighed in a 20 mL vial (Agilent Technologies, Santa Clara, CA, USA) and immediately screw-capped with a laminated Teflon-rubber disc, for headspace SPME (HS-SPME) extraction of volatile compounds. Samples were equilibrated for 15 min at 37 \({}^{\circ}\)C, and successively the extraction process was carried out for 30 min at the same temperature (ensuring a homogeneous temperature for sample and headspace).  
After extraction, the fiber was desorbed and maintained at 260 \({}^{\circ}\)C during 8 min in the injection port of the gas chromatograph-mass spectrometer (GC-MS) system (splitless mode; helium pressure 9.59 psi). Helium was used as the carrier gas with a constant flow of 1.2 mL/min. For volatile separation, a DB-624 capillary column (30 m, 0.25 mm i.d., 1.4 \(\upmu\)m film thickness; J&W Scientific, Folsom, CA USA) was employed. The oven temperature program was isothermal for 10 min at 40 \({}^{\circ}\)C, raised to 200 \({}^{\circ}\)C at a rate of 5 \({}^{\circ}\)C/min, successively raised/increased to 250 \({}^{\circ}\)C at a rate of 20 \({}^{\circ}\)C/min, and held for 5 min (total run time for analysis was 49.5 min). Injector and detector temperatures were both set and maintained at 260 \({}^{\circ}\)C. The mass spectra were acquired using the 5977B selective detector working in electronic energy at 70 eV, with an electron multiplier voltage of about 900 V and collecting data at 2.9 scans/s over the range \(m\)/z 40-550 in scan acquisition mode. The mass source was maintained at 230 \({}^{\circ}\)C, while the mass quad was set at 150 \({}^{\circ}\)C.  
After chromatographic analysis, data processing and identification were realized with the software MassHunter Quantitative Analysis B.07.01 (Agilent Technologies), where the integration was carried out with the Agile2 algorithm, while peak detection was realized by deconvolution. Compounds identification was accomplished by comparing their mass spectra with those included in the NIST14 library (National Institute of Standards and Technology, Gaithersburg, MD, USA) (2014, version 2.2). In particular, the volatile compounds were considered appropriately identified when their spectra exhibited a library match factor \(>\) 85%, and were included in the data analysis only if they appeared in more than 50% of the group of samples (_e.g._, in 10 out of the 19 and 14 out of the 27 samples of foal meat from the BU and JN breeds, respectively). Finally, after integration, peak detection and identification of each compound, the extracted ion chromatogram (EIC) from the quantifier ion was obtained from each peak. The final outcomes were expressed as area units of the EIC \(\times\) 10\({}^{4}\) per gram of fresh sample (AU \(\times\) 10\({}^{4}\)/g of fresh meat).