Partial replacement of soybean meal with full-fat black soldier fly larvae meal in plant-based nursery diets did not influence fecal Escherichia coli colony forming units or improve fecal consistency when pigs were weaned into non-disinfected pens

At weaning, one hundred pigs (21 d of age; 6.96 ± 0.23 kg BW) were used to determine the effect of partially replacing soybean meal (SBM) in corn- and SBM-based nursery diets on growth performance, fecal scores, Escherichia coli (E. coli) colony forming units (CFU), and cecal mucosal microbial profile when weaned into non-disinfected nursery pens. Pens were randomly assigned to one of four dietary treatments (n = 5): high-complexity (contained highly digestible animal proteins and 10.8% SBM) with and without 3,000 ppm ZnO (HC + and HC−, respectively; representative of commercial diets), low-complexity (corn- and SBM-based; 31.8% SBM; LC), or LC with 30% inclusion of full-fat black soldier fly larvae meal (BSFLM) to partially replace SBM (LCFL; 8.0% SBM). Diets were fed for 14 d (phase I), followed by 4 wk of a common corn-SBM diet (phase II). Fecal E. coli CFU and cecal mucosal microbial 16s rRNA community profiles were assessed 7 d after weaning. During phase I, pigs fed LC and LCFL had lower average daily gains (P < 0.05) than pigs fed HC + and HC−, which were not different. Average daily feed intake was not different for pigs fed LC and LCFL, but lower than for pigs fed HC− (P < 0.001); pigs fed HC + had greater feed intake in phase I vs. all other treatment groups (P < 0.001). Upon nursery exit, only pigs fed LCFL had lower BW than pigs fed HC− (P < 0.05), with intermediate values observed for HC + and LC. Day 3 fecal scores were greater for pigs fed LCFL vs. HC + (P < 0.05) and day 7 E. coli CFU were greater for all treatment groups vs. HC + (P < 0.001). Pigs fed HC− (P < 0.01), LC (P < 0.05), and LCFL (P < 0.05) had lower alpha diversity for cecal mucosal microbiota compared to HC+. At the genus level, pigs fed LC had lower Lactobacillus relative abundance vs. pigs fed HC + (P < 0.01). Therefore, BSFLM can partially replace SBM without sacrificing growth performance vs. nursery pigs fed corn- and SBM-based diets, but both groups had reduced phase I growth performance vs. pigs fed highly digestible diets containing animal proteins when weaned into non-disinfected pens. The BSFLM did not influence fecal E. coli CFU or improve fecal consistency after weaning and therefore, is less effective at minimizing digestive upsets vs. HC + diets.