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Abstract：
The Slovenian Krškopolje pig is the only preserved local autochthonous breed, appreciated mainly for its good meat quality and considered more appropriate for processing into dry-cured products. However, the biological characteristics of the skeletal myofibers of the Krškopolje breed, specifically the heavy myosin chain-based contractile and metabolic phenotypes that could affect meat quality, have not been established under different husbandry systems. The breed is generally maintained in either conventional indoor or organic systems. In the present study, the morphological, contractile, and metabolic properties of myofibers of the longissimus dorsi muscle were compared between animals reared in either an organic or a conventional indoor system. The myofibers were studied using immunohistochemical and succinate dehydrogenase (SDH) activity-based classification, histomorphometric assessment, and qPCR. Results revealed that the organic production system influenced the composition of the longissimus dorsi myofiber type, characterized by a smaller myofiber cross-sectional area, a shift toward oxidative (SDH-positive) myofiber types, increased relative expression of myosin heavy chain (MyHC) isoforms I, IIa, and IIx, and downregulation of MyHC IIb. On the contrary, no apparent effect was observed on the metabolic phenotype of the myofiber as assessed through relative mRNA expression of energy metabolism-related genes [peroxisome proliferator-activated receptor gamma, coactivator 1 alpha (PGC-1α), peroxisome proliferator-activated receptor gamma (PPARγ), lipoprotein-lipase (LPL), carnitine palmitoyltransferase 1B (CPT1B), glycogen synthase 1 (GYS1), hexokinase 2 (HK2), and fatty acid synthase (FASN)]. Differences in MyHC expression were largely corroborated by the histochemical classification, indicating that the contractile protein content is directly regulated by the MyHC genes. A correlation between the muscle contractile and metabolic phenotypes was not established, except for that between the HK2 and MyHC I genes. In conclusion, the present study showed an evident effect of rearing on the longissimus dorsi myofiber contractile phenotype but not the metabolic phenotype. Moreover, obtained data suggest that rearing the Krškopolje pig breed in a conventional system would result in an increased fiber size and a greater proportion of type IIb myofibers, which are known to be negatively correlated with some meat quality traits.
摘要：
斯洛文尼亚Krškopolje猪是唯一保存完好的当地本土品种，主要是因为它的肉质好，被认为更适合加工成干腌制品。然而,Krškopolje品种的骨骼肌纤维的生物学特性，特别是基于重肌球蛋白链的收缩和代谢表型，可能影响肉质，没有在不同的畜牧业系统下建立。该品种通常保存在常规的室内或有机系统中。在本研究中,形态学,收缩，并比较了在有机或常规室内系统中饲养的动物的背最长肌肌纤维的代谢特性。使用免疫组织化学和基于琥珀酸脱氢酶（SDH）活性的分类研究了肌纤维，组织形态学评估，和qPCR。结果表明，有机生产系统影响背肌肌纤维类型的组成，具有较小的肌纤维横截面积，向氧化（SDH阳性）肌纤维类型的转变，肌球蛋白重链（MyHC）亚型I的相对表达增加，IIa,和IIx，和MyHCIIb的下调。相反,通过能量代谢相关基因[过氧化物酶体增殖物激活受体γ，共激活剂1α(PGC-1α)，过氧化物酶体增殖物激活受体γ（PPARγ），脂蛋白-脂肪酶（LPL），肉碱棕榈酰转移酶1B（CPT1B），糖原合成酶1（GYS1），己糖激酶2（HK2），和脂肪酸合成酶（FASN）]。MyHC表达的差异在很大程度上由组织化学分类证实，表明收缩蛋白含量直接受MyHC基因调节。肌肉收缩和代谢表型之间的相关性尚未建立，除了HK2和MyHCI基因之间的基因。总之,本研究表明，饲养对背最长肌肌纤维收缩表型有明显影响，但对代谢表型没有影响。此外，获得的数据表明，在常规系统中饲养Krškopolje猪品种将导致纤维尺寸增加和IIb型肌纤维比例增加，已知与某些肉质性状呈负相关。
