Response to dietary digestible energy concentration in growing pigs fed cereal grain-based diets1

Understanding how energy is utilized by the pig, and how the pig responds to changes in dietary energy concentration, is essential information in determining the optimal concentration of dietary energy under farm conditions, which are often highly diverse. The objective of these experiments was to determine how changes in dietary DE concentration, achieved through graded changes in diet composition, would affect the performance and carcass composition of growing pigs. In Exp. 1, which was conducted in a research facility, 300 pigs (31.1 +/- 2.6 kg) were assigned to diets containing 3.09, 3.24, 3.34, 3.42, or 3.57 Mcal of DE/kg. Experiment 2, which was conducted at a commercial swine farm, involved 720 pigs (36.8 +/- 5.9 kg) assigned to diets containing 3.12, 3.30, or 3.43 Mcal of DE/kg. Increased DE concentration was attained by using more wheat, soybean meal, and fat and less barley; true ileal lysine was adjusted as DE increased, and minimal AA:lysine ratios were maintained. In Exp. 1, ADG improved linearly as the energy content of the diet increased (P = 0.03). Feed intake decreased (P < 0.001) and feed efficiency and daily caloric intake improved (P = 0.005) with increased DE content. Variability in growth was not affected by treatment. Carcass index and LM thickness were not affected by increasing dietary DE content; backfat thickness, however, was increased (P < 0.001). In Exp. 2, overall ADG was unaffected by dietary energy content, although an improvement in growth was observed until the pigs reached approximately 80 kg of BW. Overall feed intake decreased with increasing energy content (P = 0.01), although this was not observed during the initial 6 wk of the experiment. Carcass index, lean yield, and backfat were not affected by increasing dietary energy content, whereas LM thickness tended to increase (P = 0.08). The value per pig was unaffected by increasing dietary energy content in both experiments, and returns above feed costs were reduced. Increasing the energy density of the diet for growing pigs through incremental changes in dietary composition had a variable impact on overall growth performance and carcass quality. Increasing the dietary DE had no effect on variations in BW at the time of marketing.