Influence of essential oil supplementation and diets with different nutrient densities on growth performance, nutrient digestibility, blood characteristics, meat quality and fecal noxious gas content in grower–finisher pigs

Ninety-six [(Landrace × Yorkshire) × Duroc] pigs with initial body weight (BW) of 23.94 ± 0.41 kg were used to investigate the effects of nutrient density and essential oils (EO) on growth performance, nutrient digestibility, blood characteristics, meat quality and noxious gas emission in grower–finisher pigs. Pigs were randomly allotted to one of 4 dietary treatments in a 2 × 2 factorial design with 2 levels of nutrient density (low or high nutrient density) and EO (0 or 0.01%) according to their sex and BW (6 replicates with 4 pigs per pen, 2 gilts and 2 barrows). The pigs were subjected to a 3-period feeding program (Table 1) consisting of grower (0 to 6 weeks), early finisher (6 to 12 weeks) and late finisher (12 to 16 weeks) periods. During weeks 0–6, feeding EO increased the average daily gain (ADG) (P < 0.01), gain/feed (G/F) (P < 0.01) and the digestibility of nitrogen (N) (P < 0.01) and energy (P < 0.05), which may have led to the increased (P < 0.05) ADG (0 to 16 weeks) as these effects were absent during other periods (6 to 16 weeks). Moreover, providing diets with low levels of nutrients reduced (P < 0.001) the ADG, average daily feed intake (ADFI) and G/F, which can also be attributed to the improvement that was observed during weeks 0–6 (ADG, ADFI, P < 0.001), 6–12 (ADFI, G/F, P < 0.001) and 12–16 (ADG, P < 0.05). Furthermore, EO increased the longissimus muscle area (LMA) (P < 0.001) and reduced the b* value (P < 0.05) and the NH3 excretion (P < 0.01) at the end of the study. Providing low nutrient diets improved the sensory evaluation (color and marbling) (P < 0.05) and reduced the LMA (P < 0.01) and fecal concentration of NH3 and H2S (P < 0.01). The interactive effects of dietary nutrient density and EO were also observed on the digestibility of dry matter (DM), N and energy (P < 0.05) during weeks 0–6, as well as on the fecal concentration of NH3 and H2S (P < 0.001) at the end of the experiment. Taken together, the results of this study indicate that the beneficial effects of EO supplementation on nutrient digestibility and fecal noxious gas content are more dramatic with high nutrient density diets.