Air quality is a highly important issue in livestock farming, particularly for poultry farms. The general public is also becoming more conscious of the unavoidable emissions from intensive livestock farming, with the latter one of the most important public issues of socio-political debate.

Ammonia is a major concern in animal production because it negatively affects animal health and welfare. Furthermore, ammonia and odor emissions from production units are undesirable for anyone living nearby. Unsurprisingly, emission reduction measures are of intense interest for those engaged in livestock production.

Multiple aspects of poultry house emissions

The proportion of ammonia emissions attributed to poultry farming is the lowest among all agricultural farming sectors. Although pollution caused by poultry farming has increased by more than 3 percent in the past 15-20 years, ammonia emissions across all animal production fell by one-quarter over the period due to the reduction in cattle and pig herds. Some fundamental correlations need to be considered in this respect, particularly that about 80 percent of water consumed by poultry is expelled through respiration and excreta.

Feed composition, environmental stress and diseases can affect the water balance in healthy animals. For example, an increase of 1 percent crude protein in the diet results in a 3 percent increase in water intake and a 10 percent increase in nitrogen excretion. In contrast, a reduction of protein in the diet leads to a reduction in nitrogen excretion.

In their study on the effects of dietary crude protein on growth, ammonia concentration and litter composition of broilers, Ferguson et al. observed that lower crude protein content (215g/kg and 11.5g/kg lysine reduced to 196g/kg and 11.3g/kg lysine) correlated positively with litter moisture content. By reducing crude protein, the ammonia concentration in the air was significantly reduced by 31 percent, while litter nitrogen content declined by 16.5 percent in dry matter.

The microbial mobilization of nitrogen in poultry excreta is relatively high because poultry excrete redundant nitrogen from protein synthesis and nitrogen from undigested protein as uric acid. Litter is perceived as "wet" when the water content of the feces exceeds 25 percent. Ammonia is formed in turn by the microbial degradation of uric acid in the wet bedding. Four molecules of ammonia are formed from one molecule of uric acid.

The higher the temperature and relative humidity of the litter, the greater is the conversion of uric acid to ammonia. Humidity increases ammonia concentrations which result in a poor housing atmosphere. As wet litter is an indicator of digestive disorders as well as energy losses due to inadequate feed conversion, this parameter is particularly important for floor rearing systems.

Increased ammonia concentration due to the moisture content of litter aggravates respiratory diseases along with the occurrence and extent of foot pad dermatitis.

In addition, the removal of poultry excrement with high nitrogen concentration contributes to air and water pollution.

Emission reduction scope

Factors such as anion-cation ratio, proportion of minerals in the diet, and various feed additives affect water intake and retention in the intestines, altering the moisture content of urine and feces. Clean indoor air contributes to nutrient intake in the digestive process, regardless of the number of animals per square meter, type of litter or condition of drinkers. The amount of uric acid excreted decreases due to better digestibility of nutrients.

Phytogenics in emission reduction

Improvements in protein digestibility will result in better utilization of dietary amino acids and thus reduce the excretion of nitrogenous compounds. As such, phytogenic feed additives have the potential to reduce emissions from poultry farms.

Studies investigating the effects of feeding two levels of dietary crude protein (21 vs. 23 percent) in combination with or without two levels of green tea (1.5 and 3 g/kg diet) or one level of oxytetracycline at 0.1 g/kg diet, revealed that decreasing dietary crude protein level to 21 percent had no adverse effects on the growth rate of broilers. Green tea supplementation at 1.5 g/kg diet increased growth rate and improved FCR by 10 percent. The authors concluded that feeding broiler chickens a 21 percent protein diet containing adequate amino acid levels when supplemented with green tea, had no negative effects on productive performance. This may contribute to less environmental pollution by reducing nitrogen excretion.

As a natural digestibility enhancer, the phytogenic flavor stimulates the internal secretion of enzymes and bile acids and enhances nutrient absorption. The most striking effect is better feed conversion, accelerated growth performance, a significant increase in carcass yield and quality, and a reduction in mortality. The latter is also based on a significant influence on the transcription factors controlling the inflammatory processes.

Experiments investigating the influence of feed additives on gas emissions are scarce. Such studies require strict experimental conditions, especially in terms of housing, temperature control, ventilation rates and measurements of gas concentrations in the air.

Several published experiments have demonstrated that protein and energy digestibility were improved in birds fed phytogenic feed additives (PFAs). Because the birds digest crude protein better with a PFA, it is also possible to reduce the dietary crude nutrients, and in this way reduce the nitrogen excretion and associated ammonia emissions.

In commercial applications in broiler houses in the Netherlands, it was ascertained that a phytogenic digestibility enhancer reduced the quantity of excreta up to 0.29kg/animal. This measurable decrease corresponds with the subjective observations of the manager that, as a whole, the litter was dry and led to better air quality. Furthermore, finishing weights were achieved earlier with the application of a PFA.

Perspectives

It is possible with the use of phytogenic digestibility enhancers to reduce ammonia content in the stall air, due to the reduction of protein in the diet specification, and improved nutrient utilization and better animal performance.

Diets with lower crude protein content are an advantage for poultry because they no longer have to make the energy-consuming conversion of excess protein into uric acid, and this energy remains available for growth. Moreover, diets with optimal protein reduce demand for water which serves the best interests of the animal while also representing economic benefits for producers.

Phytogenic feed additives comprising single or combinations of components have significant potential as new generation feed additives capable of reducing poultry house emissions. An increasing demand for animal protein on one hand, and stricter regulations of animal welfare and environmental protection on the other, makes further improvement of current production techniques mandatory.