Research on the Optimization of Dietary Energy Supply in Growing and Fattening Pigs Under a Low-Temperature Environment

The purpose of this study was to investigate the effects of the optimization of dietary energy supply on the growth performance, nutrient digestibility, energy metabolism, nutrient oxidation, slaughter performance, and meat quality of growing and fattening pigs under a low-temperature environment. In this study, forty-eight 60-day-old growing barrows (Duroc × Landrace × Large White) with an initial body weight of 31.24 ± 3.56 kg were completely randomized into two treatment groups, with four replicates in each treatment group and six pigs in each replicate. The two groups were fed diets with equal protein levels and different energy levels (a conventional diet and an energy-optimized diet); the dietary energy level was increased by 8% by adding 6% fat, and the two groups were kept at the same ambient temperature (10 ± 1 °C) all day. After 5 d of prefeeding, the final weight reached approximately 110.00 kg prior to slaughter (99 days of age), and four pigs with a body weight of about 80.00 kg were selected in the two groups for digestion, metabolism, and respiratory calorimetry. The results showed that the average daily feed intake of the TES group (energy-optimized diet group, high fat and energy) was lower than that of the CON group (conventional diet group, normal fat and energy) (<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 (60-110 kg) (<i>p</i> < 0.05). Compared to the CON group, fat and energy digestibility in the TES group were higher (<i>p</i> < 0.05), fecal nitrogen and urine nitrogen were lower (<i>p</i> < 0.05), the nitrogen deposition rate increased (<i>p</i> < 0.05), and fat oxidation and the sedimentation energy rate also increased (<i>p</i> < 0.05). The serum triglyceride concentration in the TES group was higher than that in the CON group (<i>p</i> < 0.05). Compared to the CON group, the carcass weight, body fat content, backfat thickness, and eye muscle area in the TES group increased (<i>p</i> < 0.05); the L* value of flesh color also increased (<i>p</i> < 0.05); and the shear force was lower (<i>p</i> < 0.05). The dietary energy should be optimized under a low-temperature environment, and the feed conversion efficiency of fattening pigs could be improved by improving dietary energy levels by adding fat, increasing the fat oxidation proportion, promoting nitrogen deposition and sedimentation energy, and improving slaughter performance and meat quality.