Effects of Dietary Energy Sources on Post Mortem Glycolysis, Meat Quality and Muscle Fibre Type Transformation of Finishing Pigs

Dietary energy source can influence muscle glycogen storage at slaughter. However, few studies have demonstrated whether the diet-induced change of muscle glycogen is achieved by the transformation of muscle fibre type. This study investigated the effects of dietary energy sources on meat quality, post mortem glycolysis and muscle fibre type transformation of finishing pigs. Seventy-two barrows with an average body weight of 65.0 ± 2.0 kg were selected and were allotted to three iso-energetic and iso-nitrogenous diets A, B or C, and each treatment consisted of three replicates (pens) of eight pigs each. Diet A contained 44.1% starch, 5.9% crude fat and 12.6% neutral detergent fiber (NDF); diet B contained 37.6% starch, 9.5% crude fat and 15.4% NDF; and diet C contained 30.9% starch, 14.3% crude fat and 17.8% NDF. The duration of the experiment was 28 days. After feed withdrawal 12 h, 24 pigs (eight per treatment) were slaughtered, samples from M. longissimus lumborum (LL) were collected for subsequent analysis. The results showed that pigs fed diet C had lesser average daily gain, average daily feed intake and back fat depth than those fed diet A (P<0.05). Diet C increased pH45min (P<0.05) and decreased drip loss (P<0.05) in LL muscles compared with diet A. Meat from pigs fed diet A showed increased contents of lactate and greater glycolytic potential (GP) compared with those fed diet C (P<0.05). Greater mRNA expression of myosin heavy-chain (MyHC)-I and IIa and lesser expression of MyHC-IIx and IIb (P<0.05) in LL muscles were found in pigs fed diet C, than in pigs fed diet A. In addition, pigs fed diet C resulted in downregulation of miR23a and upregulation of miR409 and miR208b (P<0.05), associated with conserved changes of their corresponding targets. These findings indicated that diets containing low starch and high fibre were beneficial in reducing muscle glycolysis, improving meat quality of finishing pigs. This reduction of GP may be partially associated with the improvement of oxidative fibre composition in LL muscle, and the change in myofibre type may be correlated with the change in the miRNA expression.