Consequences of a low protein diet in the liver and longissimus dorsi transcriptome of Duroc x Iberian crossbred pigs

Low protein diets supplied during the growing period of pigs can diminish their growth rate and increase the intramuscular fat (IMF) content which affects the sensorial and technological characteristics of the traits. In the present study, the effects of a low protein diet supplied during the growing diet of Duroc x Iberian crossbred pigs on several phenotypic traits and liver and longissimus dorsi transcriptome, were analysed 20 days after the differential treatment was started (EARLY) and at the end of it (FINAL). A total of 20 crossbred pigs were assigned to two different dietary treatments during the growing period: a control diet (C) and a low protein diet (LP) with the same energy and lower levels of raw protein (11%) and lysine (0.60%). The transcriptomes of liver and longissimus dorsi were quantified through RNAseq. A total of 134 differentially expressed annotated genes and new isoforms (DEGs) between C and LP diets in liver of EARLY animals; 480 DEGs in liver of LATE animals, and 128 DEGs and 68 DEGs in longissimus dorsi of EARLY and LATE animals were detected. The functional analyses revealed that low protein diet diminishes the expression in liver of genes codifying for proteins involved in immune system both in EARLY and LATE animals, affects the expression of genes involved in cholesterol homeostasis in liver and in the energy process and growth in longissimus dorsi. Pigs fed with LP diet had not higher IMF content than C ones, although some lipogenesis genes such as FASN, SCD or SREBF1 were higher expressed on their liver. A low protein diet supplied during growing period affects multiple biological process that could compromise the immune and energy state of the Duroc x Iberian crossbred pigs. These results point out that we should be very cautious before implementing this type of regime in Duroc x Iberian pigs. Overall design: A total of 20 Duroc x Iberian crossbred pigs were assigned to two different dietary treatments during the growing period: a control diet (C) and a low protein diet (LP) with the same energy and lower levels of raw protein (11%) and lysine (0.60%). A total of 10 animals (5 per diet) were slaughtered 20 days after the differential diet treatment started (EARLY), and the remaining 10, at the end of the growing period (LATE). Liver and longissimus dorsi samples were taken after the slaughter, the RNA was extracted and pair-end libraries were constructed.