There is evidence that spontaneous fermentation frequently occurs in liquid pig feed that is intended to be delivered as fresh liquid feed, often with a resultant deterioration in the microbial and nutritional quality of the feed, which can negatively affect pig health and growth. Strategies including controlled fermentation with microbial inoculants, pre-fermentation or soaking of the cereal fraction of the diet, enzyme supplementation and dietary acidification have been employed to inhibit pathogens and prevent deterioration of feed nutritional quality, with promising results obtained in many cases. This review evaluates the impact of these strategies on the microbial quality of liquid feed and discusses how they can be further improved. It also investigates if/how these strategies impact the pig gut microbiota and growth performance of liquid-fed pigs. Finally, we review liquid feed system sanitisation practices, which are highly variable from farm to farm and discuss the impact of these practices and whether they are beneficial or detrimental to liquid feed microbial quality. Overall, we provide a comprehensive review of the current state of knowledge on liquid feed for pigs, focusing on factors affecting microbial quality and strategies for its optimisation, as well as its impact on the pig gut microbiome.

Aims: To investigate the effect of liquid feeding system sanitization on the bacteriome and mycobiome of feeding system surfaces and liquid feed. Methods and results: High-throughput 16S and ITS2 rRNA amplicon sequencing was performed on surface swabs and feed samples collected during a previous liquid feeding system sanitization experiment. Results confirmed that feed pipeline surface biofilms were disrupted post-cleaning (PC). Pre-cleaning, the pipeline was dominated by Lactobacillus, Leuconostoc and Apiotrichum. Microbial diversity increased PC, with Jeotgalicoccus and Brachybacterium predominating, although Lactobacillus became predominant again between wk8-wk10 PC. Sanitization also impacted the feed microbial profile, with decreases in Lactobacillus, Leuconostoc, and Chryseobacterium observed in the mixing tank feed. Weissella and Kazachstania became predominant in the trough-sampled liquid feed PC. Despite sanitization, spontaneous fermentation was still observed in the feed, evidenced by decreased abundance of spoilage-associated Pantoea and Pseudomonas between the mixing tank and troughs and a concomitant increase in Lactobacillus. Nonetheless, previously reported improvements in feed quality PC suggest the changes in the liquid feed microbiota were beneficial. Conclusions: Intensive cleaning and subsequent daily acid-rinsing of the feeding system disrupted feed pipeline biofilms, reduced spontaneous fermentation and improved liquid feed quality. Therefore, we recommend liquid feeding system sanitization between batches of grow-finisher pigs followed by maintenance acid-rinsing.

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.