Effect of Excessive or Restrictive Energy on Growth Performance, Meat Quality, and Intramuscular Fat Deposition in Finishing Ningxiang Pigs

This study investigated the effects of excessive or restrictive energy on growth performance, meat quality, intramuscular fat (IMF) deposition, and related gene expression in finishing Ningxiang pigs. A total of 36 Ningxiang pigs (43.26 ± 3.21 kg) were randomly assigned to three treatments (6 pens of 2 piglets per treatment) and fed by one of three dietary treatments until the pigs of each treatment weighed approximately 75 kg equally. The three treatments were control diet (digestible energy, DE:13.02 MJ/kg, CON), excessive energy diet (DE 15.22 MJ/kg, EE), and restrictive energy diet (DE 10.84 MJ/kg, RE). Results showed that EE improved average daily gain (ADG) and feed conversion ratio (FCR) (<i>p</i> < 0.01), while nothing significantly changed by RE except FCR increasing (<i>p</i> < 0.01). EE increased the content of IMF and triglycerides (TG) (<i>p</i> < 0.05), L*_24h and b*_45min (<i>p</i> < 0.01), while decreasing cooking loss and meat tenderness in longissimus thoracis (LT) (<i>p</i> < 0.05). b*_24h was significantly increased with the increase of energy level (<i>p</i> < 0.01). Meanwhile, EE increased the cross-sectional area (CSA) of muscle fiber and the mRNA expression of myosin heavy chain (<i>MyHC</i>) <i>IIb</i>, acetyl CoA carboxylase (<i>ACC</i>), fatty acid synthase (<i>FAS</i>), and adipocyte fatty-acid binding protein (<i>FABP4</i>) (<i>p</i> < 0.05). In addition, throughout: A diet supplemented with excessive energy promoted IMF deposition by positively changing lipogenic potential while decreasing tenderness by increasing glycolytic muscle fibers, which together affected meat quality. In terms of growth performance and meat quality, the present study suggests that the low-energy diet is suitable for finishing Ningxiang pigs.