Effects of dietary energy density and apparent ileal digestible lysine:digestible energy ratio on growth performance, meat quality, and peroxisome proliferator-activated receptor γ (PPARγ) gene expression of muscle and adipose tissues in Landrace×Rongchang crossbred pigs

This study was conducted to evaluate the effects of dietary digestible energy (DE) density (13.0 or 14.5MJ/kg) and apparent ileal digestible lysine:energy (Lys:DE) ratio (0.4, 0.5, and 0.6g/MJ) on growth performance, meat quality, and PPARγ gene expression of muscle and adipose tissues in Landrace×Rongchang crossbred pigs. One hundred and eight (71.22±0.04kg body weight) crossbred (Landrace×Rongchang) castrated male pigs were blocked by BW and allotted to 36 pens (three pigs per pen), and pens were randomly assigned within blocks to one of six dietary treatments arranged in a 2×3 factorial design, with two DE levels (13.0 or 14.5MJ/kg) and three Lys:DE ratios (0.40, 0.50, or 0.60g/MJ). Over the 46-d trial, dietary energy density had no effect on average daily gain (ADG) (P=0.48), however, pigs fed high-energy diets had decreasing average daily feed intake (ADFI) and the ratio of feed intake and gain (F/G) (P<0.05). Feeding of the diet with the highest Lys:DE ratio resulted in increased F/G (P<0.05) compared with other experimental diets. Increasing energy density increased hot carcass, dressing percentage and intramuscular fat (IMF) content (P<0.05). Furthermore, IMF content decreased with increasing Lys:DE ratio (P<0.05). An energy density×Lys:DE ratio interaction on slaughter weight and shearing force was observed (P<0.05). In addition, pigs fed 14.5MJ/kg had decreasing IMF content as Lys:DE ratio increased (linear and quadratic, P<0.05), but increasing muscle pH45min (linear, P<0.05). There was a quadratic effect on shearing force (P<0.05) as Lys:DE ratio increased for pigs fed 13.0MJ/kg. Increasing dietary DE enhanced the expression of PPARγ (P<0.05) in muscle tissues, whereas the mRNA levels of PPARγ decreased (P<0.05) as Lys:DE ratio increased. The results of this study indicated that a reasonably reduced Lys:DE ratio diet increased intramuscular fat deposition and improved pork tenderness. This could be partly related to the increased gene expression of PPARγ in muscle tissues.