Nutritional strategies to mitigate NH3 in broiler production
To achieve a reduction in indoor NH3 concentrations, various interventions are possible. Good ventilation management can act to remove NH3 from the broiler house, but this does not prevent the formation of NH3 inside of the broiler house. Nutritional strategies are the key to decrease the indoor concentration of NH3 and subsequently NH3 emissions by reducing the amount of nitrogen excreted by the broilers or limiting the amount of NH3 volatilized from the litter.
Nitrogen excretion is highly correlated to nitrogen intake. Reduced crude protein diets (supplemented with synthetic amino acids to maintain optimal amino acid ratios) have been shown to reduce nitrogen excretion and NH3 emissions in broilers and broiler breeders. By avoiding the overfeeding of crude protein and amino acids, the fraction of uric acid excreted by the bird will be reduced. This can significantly impact NH3 formation and volatilization as uric acid nitrogen is degraded more rapidly than nitrogen that is excreted via the faeces. Furthermore, a lower uric acid excretion by the bird will also cause a lower water intake (leading to drier litter) and may reduce the incidence foot pad dermatitis and hock burn in broilers. Another approach to reduce the protein intake of broilers is by implementing phase feeding. This involves the adjustment of the dietary nutrient content closer to the requirements of the broilers in order to avoid the overfeeding of protein and amino acids. In broilers, the application of a 6- instead of a 4-phase feeding program reduced NH3 emissions by 22%. A decrease in the dietary crude protein content of broiler feeds generally involves reducing the amount of soybeans and soybean meal in the diet. These feedstuffs are high in potassium and their reduction can decrease the dietary electrolyte balance (Na + K – Cl), which in turn can lead to a lower water intake and a reduced litter moisture content. A lower litter moisture content can reduce the formation of NH3.
The inclusion of a range of feed enzymes and additives is already standard practice in commercial broiler feeds. As enzymes such as amylase, xylanase, protease, and phytase can improve the utilisation of nutrients such as protein, the excretion of nitrogen can be reduced and, as a consequence, the formation and volatilization of NH3 from the litter. Furthermore, the addition of enzymes to broiler feeds should allow for a dietary crude protein reduction. The water binding capacity of clays such as zeolites can increase the dry matter content of the excreta and, consequently, of the litter. Furthermore, clinoptilolite has a high cation exchange capacity and therefore high affinity toward NH4+ and NH3. The adsorption of NH3 by clinoptilolite can improve intestinal health and may prevent the volatilization of NH3 from the broiler litter. Saponin extracts are well-known for their use in reducing NH3 emissions and odour. Saponins have various modes of action and can act to reduce NH33 emissions by directly binding to NH3, improving the digestibility of nutrients such as protein, or inhibiting the enzymes involved in the conversion of uric acid to TAN.
The inclusion of fermentable fibres such as distiller’s dried grains with solubles (DDGS), wheat middlings, or soybean hulls in the diet may also contribute to reduce NH3. The microbial fermentation of these fibrous feedstuffs causes the production of volatile fatty acids which can lower the pH of the excreta and increase the non-volatile NH4+ fraction of the TAN.
In order to ensure a sustainable broiler industry, NH3 emissions should be reduced. Nutritional strategies are essential to reduce the NH3 originating from broiler production at the source. A reduction in NH3 will have a positive influence on the indoor climate and, consequently, the well-being of the animals and the farmers will be improved.