Comparative evaluation of probiotic, bacteriophage, and combined additive strategies after antibiotic use in weaned pigs

This study investigated whether the functional efficacy of probiotics (PRO), bacteriophages (BAC), and a phytogenic–β-glucan multi-component blend (COK) differs depending on the timing of administration relative to in-feed antibiotic (ANT) exposure in weaned pigs. A total of 120 piglets were assigned to five treatments: CON (basal diet), ANT (d 0-7 supplementation antibiotic), ANP (d 0-7 supplementation antibiotic + d 8-21 supplementation probiotics), ANB (d 0-7 supplementation antibiotic + d 8-21 supplementation bacteriophage), ANC (d 0-7 supplementation antibiotic + d 8-21 supplementation of multi-component blend). Growth performance, fecal consistency, nutrient digestibility, blood hormones, inflammatory cytokines, and hair cortisol were evaluated over a 21-day period. No additive exerted measurable effects during the antibiotic administration period (week 1), indicating that amoxicillin masked functional responses during early post-weaning. Pigs receiving ANP and ANC exhibited higher overall average daily gain and average daily feed intake than CON (p<0.05). The ANC group showed greater crude protein digestibility than CON and ANT during week 3 (p<0.05). ANP, ANB, and ANC supplementation increased serum IGF-1 than CON at d 21 (p<0.05). Both ANP and ANC tended to attenuate inflammatory cytokines in week 3, whereas ANB supplementation produced minimal effects (p=0.051). Fecal score and hair cortisol were unaffected across treatments (p>0.05). These results demonstrate that functional additives provide limited benefit when co-administered with antibiotics but become effective once antibiotics are withdrawn, highlighting the importance of timing when integrating additives into antibiotic-restricted weaning programs.