Effects of the Ratio of Lysine to Digestible Energy Level in the Diet on the Expression and Activity of Transcription Factors Involved in Lipogenesis in Rongchang Pigs

This study was conducted to determine the effects of varying the ratio of lysine to digestible energy level on the activity and gene expression of the transcription factors peroxisome proliferator-activated receptor-γ(PPAR-γ)and CCAAT/enhancer-binding protein-α and-β(C/EBP-α and C/EBP-β)to better understand the regulatory mechanisms controlling adipogenesis in fat and muscle tissue of the Rongchang pig.A total of 144 castrated Rongchang pigs weighing approximately 20 kg were used in a 2×2 factorial design experiment.Diets were formulated to contain a high(14.22 MJ/kg)or low(13.11 MJ/kg)digestible energy(DE)level.Within each energy level,pigs were fed diets containing a high lysine∶DE ratio(0.67,0.53,or 0.42)or a low lysine∶DE ratio(0.49,0.38,or 0.30)during the periods from 20 to 50 kg,50 to 80 kg,and 80 kg to slaughter,respectively.Each diet was fed to six replicate pens,each containing nine pigs.When the pigs reached average live weights of 20,35,60,and 90 kg,one pig from each of the replicates was chosen at random and slaughtered.Samples of back fat and longissimus dorsi muscle were collected for the assessment of transcriptional factor.The results showed that feeding a high DE level significantly increased(P<0.05)the expression of PPAR-γ at 60 and 90 kg in muscle and at 35,60,and 90 kg in back fat.Energy level also significantly increased the expression of C/EBP-β at 35 and 60 kg in both muscle and back fat(P<0.05).Higher dietary lysine increased the expression of C/EBP-β in muscle at 35 and 90 kg(P<0.05),but decreased the expression in back fat at 35(P=0.03)and 90 kg(P=0.09).The lysine level increased the expression of PPAR-γ in muscle at 60 kg only.Energy level and lysine content had no significant effects on promote the activity of PPAR-γ,C/EBP-α,or C/EBP-β either in muscle or in back fat at any level of the body weights tested.Collectively,these data indicated that dietary energy density and lysine level were equally important for lipid deposition in muscle tissue,whereas dietary energy density was more important than lysine level for fat deposition in fat tissue.