Evaluation of feeding a Bacillus-based probiotic with Rhizopus oligosporus biomass in nursery pigs

Abstract Text: High grain prices, biofuels, and severe weather events are defining how we utilize crops used for livestock production. The need for alternative feed sources and resource conservation (water, energy etc…) has become more apparent. Previously, our group has shown that fungal biomass produced by growing Rhizopus microsporus var. oligosporus (RO) on thin stillage leftovers from the ethanol process can be used as an alternative feed source in nursery pigs. Digestibility was decreased at 20% inclusion and lysine availability of RO biomass was 54%. However, the limitation in nutrient digestibility may be due to the presence of chitin, a non-starch polysaccharide. The objective of this project was to examine the use of the probiotic (Pr) Bacillus subtilis (chitinase producer) to increase digestibility of RO biomass in nursery pigs. Using a 2 x 2 factorial arrangement, 40 barrows (10.6 ± 1.52 kg BW) were assigned to four corn-SBM based diets containing the digestibility marker titanium dioxide (n=10/trt):  0%ROPr-, 0%ROPr+, 20%ROPr-, or 20%ROPr+. Pigs were fed ad libitum and performance was recorded weekly for 28 days and ADG, ADFI and G:F calculated. Body composition was assessed using a serial slaughter technique. Four additional barrows of the same initial BW were euthanized to establish the initial body composition. Total tract fecal collections were taken in the final week. Thereafter, pigs were euthanized for distal ileum contents and whole body composition. Digesta and fecal samples were analyzed for DM, N, energy, and titanium dioxide. Initial and final slaughter group body composition was assessed using dual x-ray absorptiometry and tissue accretion rates calculated. Data were analyzed with a mixed model with fixed effects RO, Pr and their interaction, with ADFI as a covariate. There was no significant RO x  Pr interaction observed in any parameters assessed. However, Pr+ increased ADG (0.47 vs. 0.45 kg/d) and G:F (0.61 vs. 0.57), compared to the Pr- treatments (P<0.05). Additionally, Pr+ increased AID of energy (59 vs. 53%, P<0.10) and N (71 vs. 55%, P<0.01). RO treatments decreased AID of N (57 vs. 69%, P<0.01). Compared to 0%RO treatment, energy (86 vs. 79%), N (84 vs. 74%) and DM (88 vs. 82%) ATTD coefficients decreased due to RO inclusion (P<0.01). Probiotic diets had little effect on ATTD. Together these data suggest probiotic modification of RO biomass had negligible effects on digestibility, tissue accretion and growth performance, however, probiotic alone did improve AID.

Keywords: Pig, Rhizopus microsporus, Bacillus subtilis