Comparison of Growth Performance and Meat Quality Traits of Commercial Cross-bred Pig 1 versus Large Black Pig Breeds

16 Background : The meat quality of different pig breeds is associated with their different muscle tissue 17 physiological processes, which involves a large variety of genes related with muscle fat and energy 18 metabolism. Understanding the differences of biological processes of muscle after slaughter is 19 helpful to reveal the meat quality development of different breeds. Therefore, 8 domestic Large 20 Black pigs (BP), a domestic breed with high fat contents in meat, and 7 Cross-bred commercial pig 21 (CP), which has a high feed efficiency with high lean meat, was used to investigate the differences 22 of their meat quality and genotype. 23 Results : The average daily gain (ADG) and hot carcass weight (HCW) of CP were higher than BP, 24 but the back-fat thickness of BP was higher than CP ( P < 0.05). The CP had higher a* but lower h 25 value than BP ( P < 0.05). The metmyoglobin (MMb) percentage of CP was higher ( P < 0.05) than 26 BP. The fat content and oxygen consumption of longissimus dorsi (LD) muscle in BP were higher 27 ( P < 0.05) than CP. BP had higher SFA and MUFA content, but CP had higher PUFA content ( P < 28 0.05). The RNA-seq was applied to compare the genome differences between the two pig breeds. 29 The RNA-seq data highlighted 201 genes differentially expressed between breeds ( P < 0.05), with 30 75 up-regulated and 126 down-regulated genes in BP compared with CP. The real-time PCR was 31 used to validate the results of RNA-seq for 8 genes, and the genes related with lipid and energy 32 metabolism were highly expressed in BP ( P < 0.05). 33 Conclusions : Based on the results, BP had superior general meat quality to CP, while the growth 34 performance of CP was better, and the genotype differences between these two breeds may cause 35 the meat quality and growth performance variance.

apparatus to extract ether without previous acid hydrolysis [11]. A 2 cm 100g thick slice cut from 106 LD muscle was placed into a polypropylene bag then stored in a vacuum package for 24 h at 4℃, 107 and the weight difference of samples were regarded as drip loss showed as percentage [12]. In order 108 to ensure stable data of color measurements, sample were bloomed for 20 min before experiment. 109 The L, a*, and b* color values were determined by a CR-400 Chroma Meter. Then, the hue angle 110 (h=arctan(b*/ a*)) and chroma (C*=(( a*) 2 +( b*) 2 ) 0.5 ) was calculated by the L, a*, and b* values. 111 112 Fatty acid composition 113 The fatty acid composition of LD muscle IMF was determined by fat extract [13]. Ten grams minced 114 meat were homogenized at 3000 rpm for 1.5 min by UltraTurrax using 0.003% butylhydroxytoluene 115 (BHT) with 200 ml Folch solution (chloroform-methanol mix 2:1). After paper-filtering (Whatman 116 No. 1) the homogenized liquid, Folch solution (50ml) was added. After filtered, the solution was 117 poured out into a decantation infundibulum mixed with 8% sodium chloride (80ml) for 24 h. The 118 solvent, collected from lipidic phase, was evaporated. After evaporation, the fatty acids composition 119 was analysis using a gas chromatography (Agilent 6890 N Network GC System). As a carrier gas, 120 helium was used at a division ratio of 1:50 with a 3.2 ml per minute flow rate. The undecanoic acid 121 methyl ester was used as an internal standard to quantify the methyl esters of fatty acids. 122 123 RNA extraction and cDNA Synthesis 124 The total RNA of longissimus dorsi muscle was extracted by TRIzol Reagent (Invitrogen, Carlsbad, 125 The cDNA was used to perform Real-time PCR in order to obtain the expression level of SLC26A7, 136 TKTL2, ACBD7, THRSP, SLPI, FADS1, ACSL6, FOS. Real time-PCR was performed using 15 μL 137 reaction system: 7.5 μL 2 × Real Master Mix; 0.75 μL upstream and 0.75 downstream primer (10 138 pmol/L); 3 μL cDNA; and 3 μL water. The reaction liquid was added on iCycler IQ 5 (Bio-Rad, 139 USA). The reactive conditions and primers were presented in Table 3 There was no significant difference of L*, b* and C* between these two groups (P > 0.05). In 179 contrast, the a* value of CP is higher (P < 0.01) than BP, but the h value of BP is higher (P < 0.05) 180 than CP. 181

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The IMF content of these two breeds was significantly different (P < 0.05), that BP is higher than 183 CP. However, the different fat content did not affect the drip loss. G Watanabe, M Motoyama, I 184 Nakajima and KJA-Ajoas Sasaki [20] pointed out that pork IMF content was not correlated with 185 drip loss, and our result had the same trend. The fat content of CP is similar to other reports about 186 white pig breeds [21,22], and the fat deposition of BP is much higher than these commercial pigs. 187 The research compared Iberian pigs and commercial cross-bred pigs showed a strong correlation 188 between IMF and backfat thickness [23]. Our data showed higher IMF and backfat deposition in the 189 British Large Black pigs, which demonstrate the similarity fat deposition pattern in local domestic 190 pigs that is different from commercial cross-bred pigs. 191 192

Oxygen consumption 193
The OCR is positively correlated with mitochondrial concentration [24]. In addition, mitochondria 194 present in the postmortem muscle can remain active and impact on the meat color through oxygen consumption [25]. The OCR of BP was higher than in CP (P < 0.01; Fig 1), so there should be more 196 mitochondria in LD muscle of BP. It was reported than muscle with more β-red fibers tended to 197 have higher OCR than muscle with more α-white fibers [26]. However, the relationship between 198 oxygen consumption and meat quality needs to be further evaluated to understand color variations 199 between the two breeds. The oxygen consumption also represents the activation of mitochondrial The fatty acid composition of LD muscles from CP and BP breeds are listed in Table 4. There was 219 a significant fatty acid composition difference between CP and BP in most comparisons (P < 0.05). 220 The total polyunsaturated fatty acids content of CP was higher (P < 0.05) than BP, such as C18:2n-221 6, C18:3n-3, C20:2, C20:3n-6, C20:4n-6, and C22:5. However, BP had higher total 222 monounsaturated fatty acid content along with higher C:10, C:20, C18:1, and C20:0 contents 223 compared to CP. The overall saturated and unsaturated fatty acids contents of CP and BP had no 224 significant differences (P > 0.05).  High-throughput sequencing is a powerful way to identify the differences in gene expression, which 240 is recently used in the study of different breeds to compared the difference of genes expression 241 related with meat quality [35]. By comparing LD muscle transcriptome differences between BP and 242 CP, we found that there was a total of 384 differentially expressed genes found between these two 243 breeds, in which 201 are highly differentially expressed (log2 Fold change ≥1 or ≤ -1; P-value 244 <0.05). Compared with CP, BP had 75 up-regulated and 126 down-regulated genes (Fig.3.). The 245 functional category of these 201 differentially expressed genes, of which 75 are highly expressed in 246 BP and 126 are highly expressed in CP, were determined by querying associated gene ontologies, 247 and they were classified into biological process, cellular component, and molecular function (Fig.4-248 6), by using DAVID bioinformatic resources. GO analysis showed the functional enrichment of 249 these differentially expressed genes, and the different genes expression may cause the diversities of 250 carcass characteristics and meat quality between these two breeds. For biological process, 5 highly 251 expressed genes in BP were related with fat cell differentiation (Fig.4). This might have led to a 252 higher IMF content of LD muscle in BP, compared with CP. In molecular function, we found that 6 253 genes, which were highly expressed in CP, were responsible for oxidoreductase activity, and these 254 genes' higher expression may cause the different OCR of the LD muscle between BP and CP. 255

Gene expression 257
In order to verify our RNA-seq expression profile data, we utilized real-time quantitative RT-PCR 258 to determine eight genes related to lipid deposition or metabolism, and the results (shown in Table  259 7.) validated the transcriptome profiles of RNA-seq. Results are presented as numerical relative In conclusion, the growth performance of CP was higher than BP, but the meat quality traits of BP 280 was better than CP. The difference in intramuscular fat content, oxygen consumption and myoglobin 281 calculation of LD muscle between these two breeds were also high. The RNA-seq and gene 282 expression data proved an efficient sight about the differences of transcriptome profiles and 283 genotype of these two breeds. Comparing BP with CP, 201 significantly differentially expressed 284 genes in LD muscle were identified.

Availability of data and materials 322
The datasets used and/or analysed during the current study are available from the corresponding 323 author on reasonable request. 324

Competing interests 325
The authors declare that they have no competing interests 326