Profiling the bacteriome of a diet fed in meal or pelleted form, delivered as dry, wet/dry, or liquid feed and its impact on the fecal and intestinal bacteriome of grow-finisher pigs

Research is limited on how feed-associated microbes impact the intestinal bacteriome, growth, and feed efficiency of pigs. The aims of this study were to (1) profile the bacteriome of a meal or pelleted diet, delivered as dry, wet/dry or liquid feed using 16S rRNA gene sequencing; (2) determine its impact on the fecal and intestinal bacteriome of grow-finisher pigs; and (3) investigate if differentially abundant bacterial taxa are correlated with growth parameters of these pigs. The experiment was a 2 x 3 factorial arrangement, with two factors for feed form (meal, pellets) and three factors for feed delivery (dry, liquid, wet/dry). It involved 216 Danavil Duroc × (Large White × Landrace) pigs penned in same-sex pen groups of 6 pigs of similar weight (average ∼33.3 kg). Pen groups were blocked by sex and weight before being randomly assigned to 1 of 6 wheat-barley-soya-based dietary treatments in a completely randomized block design: (1) Dry meal; (2) Dry pellets; (3) Liquid meal; (4) Liquid pellets; (5) Wet/dry meal; (6) Wet/dry pellets. Diets were fed on an ad-libitum basis for 64 d. Liquid feed was prepared at a water:feed ratio of 2.5:1 (fresh matter basis). Dry feed was sampled from silos and bags, and liquid feed from mixing tanks and troughs. Bacterial richness was lower in the dry pellets compared to meal (P ≤ 0.05). The liquid feed bacteriome was more diverse than that of dry feed (P ≤ 0.001). Weissella and Leuconostoc had higher relative abundance (RA) in residual trough-sampled liquid feed compared to mixing tank and fresh trough-sampled feed. The ileal bacteriome was more diverse (P ≤ 0.01) in meal-fed than pellet-fed pigs, with higher RA of Megasphaera and Mitsuokella, while Streptococcus and Escherichia-Shigella had greater RA in pellet-fed pigs (P ≤ 0.01). Lactobacillus was enriched in the intestinal digesta of liquid meal-fed pigs (P ≤ 0.05), corresponding with its predominance in this diet. Liquid meal-, liquid pellet-, and wet/dry pellet-fed pigs had the highest average daily gain (P < 0.001). Feed conversion efficiency (FCE) was better in dry pellet-fed compared to liquid-fed pigs (P < 0.001). Leuconostoc (associated with feed fermentation) was most abundant in the feces and ileal digesta of liquid-fed pigs and correlated with poorer FCE (P ≤ 0.05). The same Leuconostoc found in liquid feed were also detected in the digesta and feces of liquid-fed pigs, implicating feed-derived bacteria as a potential cause of the poorer FCE of liquid-fed pigs.