Litter additives have traditionally been used to control ammonia production from litter (Ritz et al., 2017; Waziri & Kaltungo, 2017) in the USA, where litter reuse is a common practice. These litter additives are also used to limit odour production, reduce solubility of phosphorus in spent litter and improve composition of spent litter for utilisation. Ritz et al. (2017) concluded that additives that can achieve multiple goals or reduce pathogen loads in end products are likely to become more popular.
Most of the litter additives that are used in the USA are not widely used in Australia, and many of the additives are not readily available, nor have they been tested. There has been limited need for these litter additives in Australia due to ample supply of fresh bedding material, and almost all meat chickens in Australia are brooded on new bedding, which significantly reduces the need for litter additives.
If you are considering multi-batch reuse of litter, brooding on reused litter, or using litter amendments, this needs to be considered in consultation with your integrator company, and will require a risk assessment as would be necessary with any alternative bedding/litter material.
Litter additives can take multiple forms, and each has a distinct mode of action. The key litter amendments identified in Ritz et al. (2017), Waziri and Kaltungo (2017) and Cockerill et al. (2020) are:
- acidifying agents—change the chemical properties of the litter (pH) and reduce ammonia generation.
- clay-based absorbents—absorb odours and reduce ammonia release by absorbing moisture.
- microbial and enzymatic inhibitors—inhibit enzymatic activity and microbial growth which contribute to ammonia generation.
- alkalisers—inactivate pathogens in manure and sewage sludge before land application and promote the rapid volatilisation of ammonia.
Ritz et al. (2017) stated that litter accumulation, litter moisture, meat chicken breed, brooding temperature program and disease challenges are among variables that influence the selection, efficacy and return on investment, with the most effective products being those that react chemically to lower the pH of the litter (i.e. acids). Low pH creates an unfavourable environment for most bacteria, including those responsible for ammonia volatilisation. The authors also note that high litter moisture can reduce the effectiveness of chemical litter additives, with their effective life being less than three weeks, which may not significantly reduce ammonia generation over the production cycle.
The use of alkaline products in the litter is not recommended because they can increase ammonia emissions from the litter. It is recommended to use acidifiers instead. They control ammonia generation effectively by creating acidic conditions in the litter which reduce or prevent the conversion of NH4 (ammonium) to NH3 (ammonia). Commercially available acidifiers include alum, sodium bisulphate, ferric sulphate, sulfuric acid and phosphoric acid (Waziri & Kaltungo, 2017).
In a review of litter amendments, Dunlop et al. (2020) found that the most widely used litter amendment products in the USA are acids that reduce the pH of the litter and hence lower ammonia emissions. Their review found, however, that the timing of application is important. For example, if ferric sulphate is used, it should be applied 2–5 days before chick placement to allow activation, while sodium bisulphate activates quicker and should be applied 24 hours before placement. In their review of litter amendments, Cockerill et al. (2020) concluded that acidifiers are the most effective amendment types, sodium bisulphate and alum being among the most commonly tested.
