Re-used or New Bedding Are Not Drivers of <em>Salmonella</em> Levels and Serovar Emergence in Commercially Farmed Broilers in Australia

<p> To inform <em>Salmonella</em> on-farm management during broiler rearing, a 2-year study on two farms compared the Australian practices of new bedding use, partial litter re-use and an alternative, full litter re-use. Six sequential commercial cycles of ~50 days each were tested on each farm, on ~day 7 from placement (litter only), prior to first thin-out, and prior to final removal (litter and ceca). A random number sample collection occurred, defined by shed supports (33, 39), different drinkers, feeders, and shed center. Across the six cycles on both farms, <em>Salmonella</em> levels in ceca just prior to thin-out on full re-use litter were higher (log 3.11 MPN/g, <em>P</em> = 0.008) than for new bedding (log 2.04 MPN/g) and partial re-use (log 2.43 MPN/g) litter (the latter two were not significantly different). Prior to final removal across all practices the <em>Salmonella</em> levels in ceca from new bedding (log 1.72 MPN/g), partial re-use litter (log 1.77 MPN/g), and full re-use litter (log 2.33 MPN/g) were not statistically different, suggesting no effect of litter practice. The <em>Salmonella</em> levels in litter prior to the first (log 1.96–2.31 MPN/g) and second (log 2.24–2.48 MPN/g) removals were also not statistically different. The emergence of <em>Salmonella</em> serovars in the partitioned chicken-free grow-out end (back) of all sheds at ~day 7 did not suggest carry-over. Both the pattern of emergence of <em>Salmonella</em> serovars and <em>Salmonella</em> levels in litter ~day 7 in the brooder-end with chickens (front), suggested the <em>Salmonella</em> present were due to flock contribution and not practice driven. The dominant <em>Salmonella</em> serovar across cycles on both farms was <em>S</em>. Sofia (75 and 77% isolates) followed by <em>S</em>. Typhimurium (11 and 17%). Irrespective of initial serovars, <em>Salmonella</em> Sofia rapidly gained dominance and displaced 14 other serovars including <em>S</em>. Typhimurium on both farms. This study demonstrates that the litter practices are not the major driver of <em>Salmonella</em> prevalence in broiler farming, supporting the commercial re-use of bedding as a sustainable farming practice in Australia. The major contributor of <em>Salmonella</em> load in production is the <em>Salmonella</em> status of the incoming flock, indicating this is the key area to focus future control measures. </p>