In Australia, the majority of broilers are reared on single-batch litter. However, production costs and concerns regard bedding material availability are forcing additional Australian producers to attempt multi-batch litter production. The Australian broiler industry is forecasted to increase 3-4% annually through 2017, while more of Australia’s producers are expected to adopt multi-batch litter production and, consequently, take on all challenges associated with it. Therefore, a study was conducted to investigate a novel litter reuse approach and its associated challenges on broiler performance and welfare, as well as to better understand both litter and intestinal microbiomes associated with this novel litter reuse approach.
The objective of the first study was to investigate the effects of reused litter on litter pH and moisture, air ammonia concentrations, and bird performance and welfare on three commercial broiler farms in New South Wales, Australia. On each farm, litter from the previous batch within six on-site sheds was assigned to one of three treatments: 1) a full cleanout replenished with new litter (NL); 2) litter reuse in the entire shed following heaping and turning (RL); and 3) RL plus the addition of an acidifying litter amendment (RL+A). Chicks were placed directly on their respective litter/bedding treatments, although placement paper was used to allow feed to be placed on the litter surface for easier chick consumption. Litter and air ammonia concentrations, live bird bodyweight (BW), and welfare measures were collected on days 0 (day of placement), 7, 14, and 35 and analyzed in a randomized block design (RBD) with repeated measures in time using the PROC MIXED procedure of SAS version 9.3. Mortality was recorded by farm staff and analyzed as a chi-square. Following heaping and turning, RL and RL+A litters were dryer (P < 0.0001) than NL litter on day of placement, with no treatment differences occurring thereafter. The pH of NL was lower (P < 0.001) than RL and RL+A at 0 and 7 d. The litter amendment failed to significantly impact litter chemistry, such that litter moisture and pH did not differ (P > 0.05) between RL and RL+A. However, litter amendment did appear to have a reducing effect on air ammonia concentrations relative to the RL treatment on two of the test farms. Overall observed early (2%) and final (6.5%) mortality rates were consistent with commercial production systems. Live bird BW did not differ (P > 0.05) between treatments on days 0, 7, or 14; however, by day 35, RL birds tended (P = 0.08) to be 102 ± 41 g and 145 ± 43 g heavier than NL and RL+A birds, respectively. Welfare measures provided no evidence of sustained reduction in welfare status of birds on reused litter, or any clear benefits or disadvantages of the litter amendment. Under proper management, results indicate bird performance and welfare can be maintained when incorporating reused litter.
The objective of the second study was to characterize and compare both the litter and intestinal microbiomes of commercial broiler chickens reared on different litter management treatments (new litter, NL; reused litter, RL; and, reused litter plus an acidifying amendment, RL+A) over the course of one grow-out period using Illumina sequencing of 16S rRNA gene amplicons. Litter and digesta (ileal and cecal) samples were collected on days 0, 7, 14, and 35. Alpha diversity indices, operational taxonomic units (OTU), and OTU abundance were analyzed in a RBD with repeated measures in time using the PROC MIXED procedure of SAS version 9.3. Ordination of beta diversity was performed using principal coordinate analysis (PCoA), and Venn diagram analysis was performed to generate the number of unique and shared OTUs across samples within treatment. As indicated by PCoA analysis and significant (P < 0.01) treatment × sampling day interactions in the analysis of dominant phyla, the NL microbiome was different from the microbiome of reused litter for at least the first two weeks of production. Firmicutes and Actinobacteria were the predominant phyla in reused litter across the duration of the study; whereas Proteobacteria was the predominant phylum in NL at d0 and second most abundant phylum in NL at days 7 and 14. RL and RL+A litter microbiomes did not differ, likely due to the inability of the amendment to lower the reused litter pH. Despite differences between NL and reused litter microbiomes, litter did not have an effect (treatment effect, P > 0.05) on ileal or cecal microbiomes. Microbial communities exhibited temporal successions (sampling day effect, P < 0.05) in the NL, ilea, and ceca. Baby chicks arrived on farm with intestinal microbiomes that exhibited considerable richness and diversity at the time of placement. Venn analysis showed that 56% of OTUs were shared across the core microbiomes of all three treatments; however, reused litter microbiomes were more similar to one another, as they shared 5 additional OTUs that were not present in the NL. These data suggest that although the microbiome may differ between new shavings and reused litter, its impact on the development of the intestinal microbiome and the performance of birds reared on those litters is not obvious. Instead, the temporal succession of the NL microbiome to become more similar to that of the reused litter microbiomes at d35 suggests that the bird may have a greater influence on the development of the litter microbiome.
The objective of the third and final study was to test the effects of in-house litter “composting” with and without the addition of an acidifying litter amendment on the abundance of enteric pathogens associated with commercial broiler production, as a means to validate alternative litter reuse management strategies for Australian producers. Specific quantitative PCR (qPCR) assays were used to quantify Campylobacter, Salmonella, generic C. perfringens, and virulent C. perfringens that carried the gene encoding NetB-toxin (netB) from samples of litter and digesta (ileal and cecal) collected on days 0, 7, 14, and 35. All missing data were assigned to the value of the detection limit for a given target sequence. Transformed qPCR data were analyzed in a RBD with repeated measures in time using the PROC MIXED procedure of SAS version 9.3. Sustained “composting” temperature >50 ºC were observed in both heaped litter piles and litter windrows at varying depths. Campylobacter was detected in 40.5% of all litter samples. It was detected in similar abundance in litter samples prior to “composting” and on d0, indicating that “composting” had no effect (P > 0.05) on Campylobacter within the litter. Both Salmonella and generic C. perfringens were not detectable in litter samples prior to “composting.” Salmonella was more abundant (P < 0.05) in fresh shavings than reused litter on days 0, 7, and 14; however, Salmonella was not detected in ileal digesta and cecal digesta samples collected from birds reared on fresh shavings for the entire grow-out period. C. perfringens was detected in all samples (litter, ilea, and ceca) only at day d7 (sampling day effect, P < 0.05). Virulent netB carrying C. perfringens was not detected in any of the samples. From these data, the effects of “composting” and litter amendment on the presence/abundance of pathogens within litter were not obvious. There were no treatment (litter) effects (P > 0.05) on the presence/abundance of pathogens in digesta samples, indicating that horizontal transmission of pathogens from the litter to intestines of birds did not occur in this study. One advantage to reused litter is that its diverse microbiome may exude competitive inhibition-like properties toward the colonization of pathogens.
Collectively, these studies present an alternative to single-batch litter production that some Australian producers may want to adopt. Despite the inherent challenges associated with litter reuse, bird performance and welfare on reused litter were comparable to if not better than that observed on single-batch litter in this study. In addition, high-throughput sequencing has revealed the microbiomes unique to both the litter and broiler gastrointestinal tract with a level of depth and clarity that have only been seen a few times before.