The Effect of Reduced Dietary Protein on Adipose Tissue in Local Krškopolje Pigs

The Slovenian autochthonous breed, Krškopolje pig, is known for high fatness and better adaptability to different environmental conditions and feed resources. However, the metabolic processes underlying these adaptations, especially in response to different diets, have not yet been studied. A deeper understanding of these mechanisms could provide valuable insights into the breed's adaptability to different environmental conditions. Therefore, the main objective of this study was to evaluate the effect of a low-protein (LP) diet on adipose tissue in Krškopolje pigs reared in either organic outdoor (n = 2 × 12) or conventional indoor (n = 2 × 14) systems. In the outdoor system, the LP diet had no effect on adipocyte size compared to the control (high-protein) diet, while it increased lipogenic enzyme activities and monounsaturated fatty acid content, and decreased polyunsaturated fatty acid content (<i>p</i> < 0.05). RNA sequencing revealed the upregulation of 28 genes and the downregulation of 37 genes. The upregulated genes were mainly involved in lipid metabolism (<i>ACLY</i>, <i>FASN</i>, <i>ACACA</i>, <i>MOGAT2</i>), oxidative stress, and mitochondrial function. In the indoor system, pigs on the LP diet had smaller adipocytes (<i>p</i> < 0.05), whereas no differences were detected in the lipogenic enzyme activities or fatty acid composition (<i>p</i> > 0.10). RNA sequencing revealed 30 upregulated and 28 downregulated genes. In the indoor system, heat shock proteins (<i>HSP70.2</i>, <i>HSPA6</i>) were upregulated in pigs on the LP diet, while genes involved in the innate immune system (<i>MSR1</i>, <i>TREM2</i>, <i>CSF3R</i>) were downregulated. To conclude, the present study showed that LP diet affected adipose tissue metabolism and gene expression in Krškopolje pigs, with different transcriptomic responses observed in outdoor and indoor rearing conditions.