Effect of energy restriction on feed efficiency, nutrient digestibility, and immune biomarkers of growing/finishing pigs

Abstract Text: Many factors affect control of feed intake and regulation of energy balance including external (e.g., environment) and internal (e.g., hormones) factors.  The objective was to evaluate effects of nutrient restriction on feed efficiency, apparent total tract digestibility (ATTD), and an immune biomarker in growing-finishing pigs.  Crossbred barrows (n = 36; initial BW = 52.3 kg) were randomly allotted to 36 individual pens with 2 dietary treatments in an 8 wk experiment. Treatments included a control (ADLIB; n = 16 pigs) diet formulated to meet or exceed 2012 NRC requirements and an energy restricted (RESTR; n = 16) diet.  Pigs maintained on RESTR were provided feed representing a 50% (wk 1) or 25% (wk 2 to 8) reduction in amount of feed relative to amount of feed provided to ADLIB pigs. All diets were corn-soybean meal-based, fed in 2 phases (phase 1, wk 1 to 4; phase 2, wk 5 to 8) and contained 0.5% TiO₂ (digestibility marker). Feed disappearance and individual BW were measured weekly for determination of ADG, ADFI, G:F. At the end of each phase, fecal samples were collected from each pig twice daily for 3 consecutive days and pooled by phase. Feces were analyzed for DM, TiO₂, and GE. Blood samples were collected from each pig (wk 0, 1, 2, 4, 6, and 8) and serum analyzed for C-reactive protein (CRP).  No differences in BW (P = 0.79) were observed on d 0 and RESTR pigs had lower (P < 0.001) BW compared to ADLIB at subsequent timepoints.  Final mean BW was 100.5 and 112.0 kg, respectively for RESTR and ADLIB pigs.  Overall, ADG (0.86 vs. 1.05 kg) and ADFI (2.65 vs. 3.44 kg) decreased (P < 0.001) and G:F (0.37 vs. 0.34 kg/kg) increased in RESTR compared to ADLIB pigs, respectively. With respect to ATTD, no differences were detected in phase 1; however, in phase 2, DM (83.45 vs. 81.62 %) and GE digestibility (82.88 vs. 80.87 %) was increased  (P < 0.008) in RESTR compared to ADLIB pigs, respectively. For CRP, no overall differences were observed; however, CRP tended to decrease (P= 0.06) in RESTR compared to ADLIB pigs in wk 1. Pigs may compensate for nutrient restriction by becoming more efficient with respect to nutrient assimilation.

Keywords: digestibility, energy restriction, feed efficiency