Research on Energy Supply Optimization of Diets for Songliao Black Growing and Fattening Pigs at a Low Ambient Temperature

The aim of this experiment is to investigate the effects of optimizing the dietary energy supply of Songliao Black growing and fattening pigs on their growth performance, nutrient digestibility, nitrogen balance, energy metabolism and oxidation energy supply, slaughter performance, and meat quality at a low ambient temperature. Forty-eight 75-day-old Songliao Black growing barrows with an initial weight of 33.38 ± 1.29 kg were randomized into two groups, with four replicates in each group and six pigs in each replicate. Two groups (CON group: low fat, normal energy; TES group: high fat, high energy) were fed isonitrogenous diets with different energy levels and fat contents. The experimental animals were raised at the same ambient temperature (10 ± 1 °C) all day. After 5 days of pre-feeding, the formal experiment began. Four Songliao Black barrows weighing approximately 80 kg were selected from each group for a five-day experimental period for digestibility and metabolism and respiratory calorimetry tests. All pigs (185 days of age) were slaughtered simultaneously at the end of the 110-day experimental period when their average body weight reached approximately 110 kg. The results showed that the average daily feed intake of the TES group was lower than that of the CON group (<i>p</i> < 0.05). Compared with the CON group, the feed-to-gain ratio was lower in the TES group during the fattening period (<i>p</i> < 0.05). Compared with the CON group, the crude fat digestibility, deposition energy, energy deposition rate, deposition energy of fat, and fat oxidation were higher (<i>p</i> < 0.05), and the intake and urinary nitrogen, carbohydrate oxidation, urinary energy, and protein oxidation were lower in the TES group (<i>p</i> < 0.05). Compared with the CON group, the serum high-density lipoprotein concentration, low-density lipoprotein concentration, and triglyceride concentration were higher in the TES group (<i>p</i> < 0.05), while alanine aminotransferase and aspartate aminotransferase concentrations were lower in the TES group (<i>p</i> < 0.05). Compared with the CON group, the backfat thickness was higher in the TES group (<i>p</i> < 0.05). Compared with the CON group, the weight gain/digestible protein and live lean meat mass/digestible protein were higher in the TES group (<i>p</i> < 0.05). Compared with the CON group, the yellowness (b*_45min) value of the longissimus thoracis was higher in the TES group (<i>p</i> < 0.05), and the shear force was lower (<i>p</i> < 0.05). Therefore, at a low ambient temperature, appropriately increasing the levels of dietary fat and energy was beneficial for improving the production performance and energy utilization efficiency and reducing CO₂ emissions and protein oxidation, saving protein resources of Songliao Black pigs.