The rapid expansion of chicken meat production in Australia has led to a scarcity of bedding materials such as wood shavings and sawdust, and, at times, rice hulls and straw, according to an article in E-Chook News from Poultry Hub, part of Poultry CRC in Australia. The natural flow on from this demand is increased pricing of new bedding materials which create a financial incentive to re-use litter for multiple batches in broiler production.

Litter quality is critical for broiler health and welfare

Reuse of litter, while common in some countries such as the US, poses problems such as diminished litter quality, carry-over of poultry or human disease organisms (pathogens) and excessive ammonia production, particularly during brooding. However, these problems can be overcome by appropriate litter treatment between batches of chickens.

Professor Steve Walkden-Brown at the University of New England leads Poultry CRC Project, 'Methods to quantify and inactivate viruses in poultry litter'. This project has focused on use of litter heaping between batches to improve litter quality and reduce the load of poultry pathogens, particularly viruses. The research team have also evaluated some treatments for the amelioration of ammonia production from reused litter.

Recently at the bi-annual Poultry Information Exchange (PIX) conference, Professor Walkden-Brown, his UNE collaborator Dr Fakhrul Islam, and recently completed Poultry CRC-supported PhD student, Michael Cressman, presented their latest findings.

Common approaches to dealing with pathogens include litter pasteurisation (using the heat generated by heaping of litter and allowing it to start composting), chemical amendment, or the ‘do nothing’ strategy.

Professor Walkden-Brown explained: “Pasteurisation usually occurs for four to 10 days with or without turning, and previous research suggests good efficacy. There are many claims of efficacy of various chemical amendments, but little in the way of verification. Finally, the 'do nothing' strategy relies on maternal antibodies within the chick to resist disease challenge. Some growers only reuse litter in the grow-out portion of the shed, using new litter in the brooding area, and this can assist with limiting early exposure to pathogens and excessive ammonia.”

The research looked at improving the efficacy of litter pasteurisation by testing the effects of covering (with tarpaulins), adding water, turning and heap size and shape on temperatures at a wide range of depths within the heap. This has given the research team more detailed profiling of temperature change in the surface layers of heaps and windrows and shown that pasteurising temperatures can extend out to within 5cm of the heap surface, reducing the requirement for turning.

In addition, the team has investigated new ways of measuring virus inactivation and the temperature-time relationships for the inactivation of five important poultry viruses, namely, Marek’s disease virus (MDV), infectious laryngotracheitis virus (ILTV), chicken anaemia virus (CAV), Fowl adenovirus (FAdV), and infectious bursal disease (IBDV).

Results to date show that inactivation of some viruses occurs at lower temperatures than previously considered necessary. For example, litter contaminated with FAdV by infected chickens lost its ability to transmit the virus to chicks placed on it after five days at 45°C, 55°C or 65°C. At 35°C, infectivity was retained for 10 days but lost by 20 days, while at 25°C infectivity was retained for 20 days. Detection of FAdV viral DNA by qPCR showed a very similar pattern, with some variations, suggesting that viral inactivation in 'composting litter' is followed rapidly by loss of viral nucleic acids.

Overall, Professor Walkden-Brown suggests that from this research project, other recent Poultry CRC work in Australia, published research and field observations, there are some clear basic principles for litter reuse. These include:

• Caked litter must be removed or pulverised before reuse. Heaping litter does not break down cake (nor, incidentally, does it kill litter beetles).
• Ammonia generation from reused litter during brooding is a significant issue. The problem can be avoided by not brooding on reused litter, using a range of litter amendments to reduce ammonia production, or ensuring reused litter is dry, friable and spread well in advance of chick placement.
• Heaping of litter between batches will significantly reduce pathogen load. Significant reductions in most infective viruses can be expected in three to four days, but the longer litter is heaped the greater the reduction that can be expected.

With regard to litter heaping, the literature and recent data suggest:

• Viral inactivation in litter is not due to achieving a specific temperature. Rather high temperatures will inactive a virus more rapidly than lower temperatures with each virus having a different time-temperature relationship. The team are close to an improved understanding of this relationship for MDV, ILTV, CAV, FAdV and IBDV.
• Turning of litter is probably not worth the effort, as recent work has shown that the volume of cool litter in heaps is relatively small and positive effects of turning on temperature generation are small. Turning cools the heap for a period of 24 hours following turning.
• Litter moisture content can affect the temperatures achieved during composting but pasteurising temperatures are achieved under a wide range of litter moisture conditions. Experimental results suggest that addition of moisture is unlikely to be warranted.
• The size of the heap to be used should be determined by the length of the pasteurisation period available. For short periods (five to six days), smaller heaps or windrows are preferable as they heat quickly. For longer periods, larger heaps are preferable as higher temperatures are reached and sustained and the deep core has time to heat up. Larger heaps also have a smaller surface area to mass ratio, so a lower proportion of cooler litter.
• Covering of heaps will generally increase average temperatures and improve the evenness of temperatures in the heap. However under conditions of cold nights and high litter moisture content, significant 'sweating' can occur under the covers, and paradoxically lead to lower surface temperatures due to evaporation. Use of covers that insulate but 'breathe' more, could overcome this problem.
• qPCR assessment of viral load in litter is likely to prove useful in determining viral presence in litter, but may overestimate infectivity of the virus.

Economic pressures and litter resource scarcity will continue to drive growers towards increased reuse of poultry litter for broiler production in Australia.

This research has improved our understanding of the inactivation of pathogens, particularly viruses in litter that is pasteurised by heaping, and we are now in a good position to optimise our approach to reuse. However, as Professor Walkden-Brown notes, “a significant barrier to litter reuse is ammonia production during brooding, and attention needs to be given to this, and to inactivation methods other than heaping, if the full potential benefits of litter reuse are to be realised”.

He added: “At present, our research group is working on integrating the available information on the effects of litter heaping on virus inactivation into a simple spreadsheet that can act as a decision support to tool. This will indicate whether litter reuse from a particular batch is sensible or not, and if so, provide recommendations for optimum treatment of litter between the batches.”

July 2014