Previous work has reported that piglets may be unable to increase feed intake to meet energy demands in low-energy diets, contrary to growing pigs. Indeed, poor feed intake in piglets occurs mainly during the first three weeks post-weaning. The approach, in this case, has been to increase the energy density of weaner diets to meet energy requirements even at lower intakes. Studies estimating the net energy (NE) requirement in piglets in the immediate post-weaning period are lacking. Hence the objective of the present study was to evaluate the dietary NE level required to optimize growth and feed efficiency in piglets during the first 21 d post-weaning. A total of 360 mixed-sex piglets (6.4 ± 0.24 kg) were housed with three pigs/pen and 24 pens/treatment (n=24 pens) and were assigned to 1 of 5 dietary treatments in a dose-response arrangement for 21-d. The experimental diets were formulated to contain graded dietary NE levels (2200, 2300, 2400, 2500, and 2600 kcal NE/kg). Diets were isonitrogenous and balanced for amino acids with a constant SID Lys/NE ratio of 1.25 across the treatments. The orthogonal polynomial contrast statement was used in a GLM model (PROC GLM, SAS studio) to determine the linear and quadratic effects of increasing dietary NE level on performance parameters. Results for the overall 21-d period indicated that, as dietary NE increased, average daily gain (ADG) increased linearly (P = 0.03). The average daily feed intake (ADFI) was not significantly (P = 0.157) affected by increasing dietary NE. The gain to feed (G:F) improved linearly as dietary NE increased (P = 0.008). Using the linear-breakpoint model (PROC NLIN), the NE estimated to maximize ADG at 305 g/day was 2475 kcal NE/kg (P = 0.008). Similarly, for maximum G:F of 0.86 g/g, the linear breakpoint model estimated the NE requirement at 2460 kcal/kg (P = 0.02). No breakpoint was estimated for ADFI, but the model tended (P = 0.08) to show a linear increase in ADFI as NE increased. In summary, the results of this study highlight that, during the first three weeks post-weaning, piglets’ feed intake may be more controlled by animal factors (gut capacity, etc.) and, to a lesser extent, energy concentration because feed intake was not affected by the dietary NE level in this study. Further, results show that ADG may be a more accurate measure of the impact of NE concentration than ADFI.
In conclusion, dietary NE levels between 2460-2475 kcal/kg during the first three weeks post-weaning may be ideal to maximize growth performance, provided all other nutrients are not limiting.