Early Litter Microbiota Changes Are Associated with Footpad Dermatitis Severity in Broilers Challenged with...

Footpad dermatitis (FPD) is a major welfare and economic concern in broiler production and is closely linked to litter conditions and bird performance. Although wet litter is a well-recognized risk factor, the contribution of early litter microbiota to paw quality remains poorly understood. In this study, we evaluated footpad lesion severity in Cobb 500 broilers at harvest (49 days) and examined litter microbiologic and physicochemical parameters throughout the grow-out period to identify factors associated with differences in paw quality. Birds were raised under four treatments: a negative control; a positive control challenged with Salmonella enterica serovar Infantis; a feed-applied Bacillus velezensis probiotic (Calsporint) with Salmonella Infantis challenge; and a litter-applied B. velezensis probiotic (proLitterbiotic) with Salmonella Infantis challenge. Footpad lesion scores differed modestly among treatments, with the positive control and birds receiving proLitterbiotic exhibiting a higher mean lesion severity score at harvest compared with the Calsporin and negative control birds. Litter moisture, water activity, pH, and metal composition varied by treatment at select time points but did not consistently align with lesion severity. Female birds in the positive control and proLitterbiotic treatments had higher mean body weights at 42 days. The 16S rRNA gene sequencing revealed that litter bacterial communities were strongly structured by time and showed treatment-associated differences immediately after placement. Early litter bacterial communities reflected contributions from the broiler house environment, starter feed, and the meconium with distinct separation between treatments receiving litter-applied probiotics and those receiving feed-applied probiotics. Although litter microbial communities converged later in the grow-out, early differences coincided with subsequent variation in paw quality. These findings indicate that poorer paw quality was associated with a combination of early changes in litter microbial communities and litter physicochemical differences, rather than a single dominant factor.