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The effect of soybean meal and its functional compounds on growth performance, fecal scores, and fecal characteristics of nursery pigs

Self, R., B. Bowen, K. Miller, T. Mitchell, T. Crome, H. Miller, J. Legacy and A. Petry

High levels of soybean meal (SBM) are deterred in nursery diets due to antinutritional factors and impacts on fecal consistency. However, SBM may improve performance in the presence of inflammatory stressors due to its functional compounds. The experimental objective was to evaluate the non-nutritive value of SBM and its functional compounds on growth performance and fecal characteristics of nursery pigs. A total of 408 newly weaned pigs with an initial BW of 5.43 ±0.77 kg were used for a 35-d study across three replications. Pigs were randomly assigned to 1 of 6 dietary treatments fed across 3 phases: d 0-7 (phase 1), d 7-21 (phase 2), and d 21-35 (phase 3). Dietary treatments consisted of a high SBM control (SBMC), a control void of SBM (SP), but included soy protein isolate and concentrate to provide amino acids similar to SBM in SBMC; SP formulated to equivalent contribution of isoflavones as SBMC (SP+ISO); SP diet fortified with soybean functional lipids to the level of SBMC (SP+LIP); SP formulated with a similar ratio of insoluble to soluble fiber as SBMC (SP+FIB); or SP diet fortified with lunasin (SP+LUN). There were 9 split-sex pens per treatment (7 or 8 pigs/pen). On d 7, 14, 21, and 35, pigs and feeders were weighed, pen fecal samples were collected, and fecal score was evaluated using a 4-point scale (1=solid; 4=liquid). Continuous data were analyzed as a linear mixed model (PROC MIXED) with treatment and period as fixed effects, replicate as a random effect, and initial BW as a covariate where appropriate. Fecal scores were analyzed using a multinomial model in PROC FREQ. Compared to SP, on d 7 and 14 pigs fed SBMC and SP+FIB had reduced fecal dry matter (DM%), but on d 21 and 35, fecal DM% did not differ among treatments (time×treatment P=0.016). There was a treatment×time interaction for fecal score, whereas on d 7, pigs fed SBMC had increased proportion of semi-liquid feces and on d 14 pigs fed SP+FIB had increased abundance of semi-liquid feces, but fecal score distribution did not differ on d 21 or 35 (time×treatment P=0.035). Fecal water binding capacity (WBC) did not differ across time (P=0.288) but relative to SP, SBMC had 30% less fecal WBC (P=0.002). There was a treatment×time interaction for ADG and ADFI. Pigs fed SP+ISO had greater ADG in phase 2, but pigs fed SBMC gained more in phase 3 (time×treatment P=0.044). Among treatments, ADFI did not differ in phase 1 and 2, but was increased in SBMC in phase 3 (time×treatment P=0.037).

Pigs fed SBMC tended to have the greatest final BW (P=0.071). Feeding SBM altered fecal characteristics in the early nursery period, but improved growth performance from d 21-35 post-weaning.