Diet formulation method influences the response to increasing net energy in finishing pigs1

Abstract

An experiment was conducted to compare the effects of increasing dietary net energy (NE) in finishing pig diets while either maintaining a standardized ileal digestible lysine:NE ratio (SID Lys:NE) or maintaining SID Lys as a constant percentage of the diet across increasing energy densities. A total of 150 pigs (Line 600 × 241; DNA, Columbus, NE; initially 35.7 kg) were used in a 91-d study. Pigs were blocked by sex and weight and randomly assigned to 1 of 5 treatments with 2 pigs per pen and 15 pens per treatment. Treatments included a low-energy control diet that was corn-soybean meal-based with added soybean hulls, and a 2 × 2 factorial arrangement of treatments with main effects of increasing dietary NE (medium or high by adding choice white grease) and formulation method (with a SID Lys:NE ratio or maintaining the same percentage SID Lys). Linear and quadratic contrasts were made using the control diet and the medium- and high-energy diets within each formulation method. Pigs and feeders were weighed approximately every 30 d to calculate average daily gain (ADG), average daily feed intake (ADFI), and gain-to-feed ratio (G:F). At the end of the experiment, pigs were sent to a commercial processing facility for carcass data collection. From days 0 to 34 and 34 to 61, ADG and SID Lys intake increased as NE increased (linear, P < 0.05) in pigs fed diets with a Lys:NE ratio, but not for those fed the same percentage Lys. As NE increased, NE intake and G:F increased (P < 0.01) in pigs fed diets with either formulation method. From days 61 to 91, increasing NE had no effect (P > 0.10) on ADG. There was no change in G:F in pigs fed diets with the same percentage Lys (P > 0.10), but G:F decreased then increased (quadratic, P < 0.01) in response to increasing NE in pigs fed diets with a SID Lys:NE ratio. Overall, increasing dietary NE increased (linear, P < 0.001) daily NE intake and G:F (linear, P < 0.018) with either formulation method. However, SID Lys intake, ADG, and hot carcass weight only increased (linear, P < 0.01) when a SID Lys:NE ratio was maintained. Increasing NE without maintaining a constant SID Lys:NE ratio increased backfat depth (quadratic, P = 0.01), whereas it did not in pigs fed diets with a SID Lys:NE ratio. In conclusion, increasing dietary energy density increased NE intake and G:F regardless of formulation method. However, a SID Lys:NE ratio must be maintained to achieve increased ADG and minimize fat deposition.

The Implications of Nutritional Strategies that Modify Dietary Energy and Lysine for Growth Performance in Two Different Swine Production Systems

“…Other studies have also reported improvements in caloric efficiency when dietary NE is reduced [26,41,42]. The unexpected effect on NEE might be attributed to an additional effect of fibrous ingredients, such as wheat middlings, by limiting physical satiety [13,43] or to an underestimation or overestimation of the NE value of some ingredients [26,36]. For instance, Kil et al [44] reported low NE values for animal fat (5.90 Mcal/kg) compared to this study (7.56 Mcal/kg).…”

“…1 as a reference, increasing SID Lys had a greater impact on the SID Lys:NE ratio than reducing NE (0.79 vs. 0.34 g/Mcal). On the contrary, Marçal et al [26] showed no effect of NE on ADG when diets were formulated with the same SID Lys and not based on SID Lys:NE. However, as in the present study SID Lys was formulated for the high NE diet, SID Lys intake was even higher in the low NE diets.…”

“…Moreover, when SID Lys (first limiting AA used as a reference in the ideal protein concept) is formulated on a ratio with energy, pigs will have a similar SID Lys intake [16]. Nevertheless, when a lower energy density impairs energy intake and diets are formulated based on a ratio between SID Lys and energy, then pigs in the low energy diets also have a lower SID Lys intake [26,27]. Therefore, sometimes it is difficult to discern whether the effects of reducing NE on ADG are due to energy or to lysine being limiting.…”

“…In contrast, in the finishing phase, reducing NE by 9.0% resulted in a 6.9% increase in ADFI and only a 3.1% reduction in NE intake. Therefore, reducing dietary NE results in an increased ADFI [39], but it negatively affects daily NE intake [14,26]; however, the effect is less severe in heavier/older pigs [13]. Similarly to Exp.…”

“…Therefore, it is relevant to work at the amino acids levels which do not limit growth performance if we want to evaluate the energy effects. Marçal et al [26] suggested that energy trials should formulate diets based on the standardized ileal digestible lysine to net energy ratio (SID Lys:NE) instead of SID Lys to report effects on ADG. However, when pigs cannot completely compensate for a reduced energy density [14], then the lower energy intake will entail a reduced SID Lys intake [27] that may limit growth performance [28].…”