High stocking density in pig production is associated with stress and reduced growth, but its effects on nasal and fecal bacterial communities, gut metabolites, and predicted functions are not fully understood. We hypothesized that high stocking density disrupts host–microbiota interactions, contributing to stress and impaired growth. In this study, 98 finishing pigs (Landrace × Yorkshire) × Duroc; 21 weeks old were assigned to high stocking density (HD: 5 pigs per pen, 0.58 m2 per pig, k = 0.029) or control (CON: 3 pigs per pen, 0.97 m2 per pig, k = 0.049) in a completely randomized block design. Growth, blood profile, and coughing index were monitored over 4 weeks. Nasal and fecal microbiota were characterized using full-length 16S rRNA sequencing, fecal metabolites were quantified by high-performance liquid chromatography, and correlations with physiological parameters were analyzed. After 4 weeks, pigs in HD group had lower final body weight (P = 0.048), average daily gain (P = 0.035), and average daily feed intake (P = 0.048), alongside elevated cortisol (P = 0.037) and coughing index (P < 0.001). Alpha-diversity of the nasal microbiota was reduced (Shannon Entropy, P = 0.009), while the fecal microbiota showed non-significant decrease. Beta-diversity revealed distinct clustering between CON and HD in nasal (P = 0.003; R2 = 0.021) and fecal (P = 0.005; R2 = 0.042) bacterial communities. Taxonomic profiling of the HD group revealed enrichment of Rothia nasimurium, Psychrobacter faecalis, and Globicatella sp. in nasal microbiota, and increased Clostridium sensu stricto 1 and Terrisporobacter, with marked decline in Lactobacillus, particularly L. amylovorus and L. johnsonii, in fecal microbiota (P < 0.05). Metabolism-related functional pathways were altered in both bacterial communities. Fecal lactate was decreased (P = 0.005) and was positively correlated with tumor necrosis factor-α (TNF-α) (P = 0.048). Biomarkers in the HD group were negatively correlated with growth performance, whereas those in the CON group showed positive correlations (P < 0.05). High stocking density impaired growth, increased blood cortisol and stress-related coughing, and altered nasal and fecal bacterial communities in finishing pigs, highlighting potential impacts of crowding on pig productivity.
Vasquez et al. (Fri,) studied this question.