Black coat variation of pig being associated with MC1R gene
Coat color is an important characteristic of various pig breeds and color variations may be useful in identifying the components of some specific crossbreeding schemes as well as contributing to the image associated with high quality regional products [12]. Here, the observation dealing with crossbreeding experiments between the Chinese indigenous CH pigs (uniform black) and imported BS pigs (domino black spotting) exhibits a “dominant black” coat color hereditary pattern. Similar result was reported that the allelism between “uniform black type” and “domino black spotting type” may also be inferred from Large Black × Berkshire cross pigs [13].
Our observed segregation results prompted the important discovery that the coat color variation of crossbreed BC pigs is determined by the single MC1R gene although more than eight color loci have been discovered [14]. Twelve mutations were screened for MC1R gene in BC crosses, which represent two typical ED1 and EP alleles inferred according to the previous report [9]. Our result indicates that the ED1 allele associated with a black coat phenotype inherits in a dominant pattern in the crossbreed BC pigs. Consequently, we have selected these the black boars and gilts genotyped with homozygous ED1ED1 since F3 progeny, and largely succeeded in the BC breed standard of black coat.
Crossbreeding improving sow reproductive performance
Level of sow productivity is one of the most importance production traits affecting the efficiency of a swine enterprise [15]. Crossbreeding programs have been used extensively to improve reproduction by exploiting breed additive effects, breed maternal effects, and heterosis. Young (1995) reported that Chinese indigenous breed Meishan, Fengjing, and Minzhu pigs can be used to produce crossbreed gilts that have a higher level of reproductive performance than Duroc crossbreed gilts [16]. Here, we found that the crossbreed BC F4 gilts have a higher litter and tear size, and meanwhile the BC gilts also are heavier at farrowing and at weaning than purebred CH gilts. Noteworthy, a mean of 12.1 pigs for total litter size and 11.4 pigs for alive litter size of BC sows has an advantage in litter size during the breeding process. Similar result also was reported that the cross sows from the Chinese native Meishan, Fengjing and Minzhu pigs show a total number of pigs born (12.0 to 11.0 pigs) and number of pigs born alive (11.3 to 10.7 pigs) per litter [14].
A favorable mean age at puberty of 178 d for crossbreed BC gilts was found although BC gilts reached puberty later than CH gilts. Similar result was reported that a mean age at puberty of 118 and 217 d for purebred Meishan and its crossbred gilts [17]. However, purebred Duroc averaged 234 d at puberty, compared with 210, 205, and 201 d for Hampshire, Pietrain, and Spot pigs [18].
Crossbreeding improving growth performance and carcass composition
Previous reports revealed that the growth performance of hybrid pigs from Duroc × Dahe, Celta × Landrace, Celta × Duroc, and Duroc × Yanan was largely improved compared with that of native pig breeds [3, 4, 6]. Here, two important growth traits including weight gain and feed efficiency are largely improved in crossbreed BC F4 pigs, indicating that the BC pigs reach a competitive slaughter age (about 200 d) at above 100 kg slaughter weight.
Meanwhile, the crossbreed BC pigs exhibit an improved carcass characteristic such as moderate lean meat ratio (~ 50%) and backfat thickness (~ 2.6 cm). The present result is similar to those of previous studies [3, 4, 6], which reported that the carcass characteristics of hybrid pigs were largely improved compared with those of the native pig breeds and a mean of 51 ~ 55% for lean meat ratio was found in the crosses from Duroc × Dahe, Celta × Landrace, Celta × Duroc, and Duroc × Yanan. According to the market demand of black pork in China, we suggest that it is perfectly suitable for black breed to reach a mean of 53 ~ 55% for lean meat ratio (about 3 ~ 5% increase). So, to achieve an ideal lean meat ratio, we will select back fat further down to 20 mm for alive back fat thickness at 180 d age in the subsequent breeding process of BC pigs.
Breed affecting meat quality characteristics
Meat quality is an important factor affecting how pork can be utilized. When choosing the best crossbreeding strategy, it is important to recognize pig breeds determine meat quality traits [19]. In this study, the crossbreed BC and purebred CH pigs produce excellent meat-quality characteristics, which showing normal and high pH values referred to the recommended normal levels (pH1 > 6.1 and pH2: 5.5 ~ 6.0) [20], normal and low meat color parameters according to NPPC (2000) standards (Minolta L-value levels of 37–49) [21], lower drip loss than those for foreign breeds with above 3% [22], and smaller muscle-fibre areas than did foreign hybrid pigs with above 5,000 µm2 [19].
As the most important parameter of meat quality, The IMF content is related to the organoleptic characteristics of pig meat and influences meat and meat-product quality [23]. An IMF content of 2 ~ 3% is suggested to be optimal for food quality [24, 25]. Interestingly, the crossbreed BC pigs in the present study exhibited relatively high IMF content (3.24%). Meanwhile, a higher PUFA:SFA ratio of IMF leads to better digestion rates and an improved digestibility of SFAs with emulsifying agents [26, 27] and the recommended PUFA:SFA ratio is more than 0.4 [28]. Here, a similar PUFA:SFA ratio of ~ 0.39 also was found in the BC pigs. The BC pig meat with high IMF content and PUFA:SFA ratio can meet the demand for high-quality niche pork products.
The super meat quality properties for the crossbreed BC pigs might be attributed to the breed attributes of their parent. Because previous studies found that the Berkshire sire pigs are superior for loin meat and eating [22], and these characteristics are, consequently, thought to attribute to its higher overall likeability score [29, 30] and improved acceptability compared with European commercial pork breeds [31]. Meanwhile, the present result and previous study indicate that the CH pigs also is characterized by superior meat quality traits [1].