Ammonia emissions can be reduced by up to 50% through nutritional strategies that reduce nitrogen in excreta and prevent ammonia from being released into the environment. The formulation of diets to more closely meet the bird's amino acid requirements and the addition of fibre are key.
Poultry manure and its nitrogenous compounds can be a potential pollutant causing eutrophication, nitrate or nitrite contamination of water, ammonia volatilisation and acid deposition in the air. Therefore, reducing nitrogen excretion and emissions in poultry manure by nutritional strategies is important to maintain a clean environment.
Protein is composed of amino acids that birds utilise for maintenance and egg production. Mature birds do not have a protein storage mechanism, so protein provided in the diet above the birds need is broken down and utilised as an energy source with excess nitrogen being excreted. Feeding reduced protein diets (-2%) can reduce N excretion with up to 24% reduction in ammonia emission. Further decreases in protein levels of the diet will, however, require that all essential amino acids are included, preferably in a crystalline form, with a careful balance of the amino acids to be considered.
A study was conducted to evaluate the effect of including various fibre ingredients in laying-hen diets on ammonia emission. It was found that the fibre ingredients led in all cases to a decrease in ammonia emission from laying-hen manure (Table 1). The effect of fibre here could be attributed to two factors:
• Fibre provides energy to bacteria in the lower gastrointestinal tract where the bacteria use nitrogen that would otherwise be excreted as uric acid for bacterial protein synthesis.
• The bacterial metabolism produces short-chain fatty acids that lower manure pH, thereby shifting ammonia (NH3) to ammonium (NH4+), which is less volatile.
The reduced ammonia emission certainly helps alleviate a number of health problems commonly observed in chicken flocks such as ascites, gastrointestinal irritation, respiratory diseases, contact dermatitis, and foot burns. Alleviation of such problems would better be achieved when fibre feeding is considered along with other management practices, such as use of nipple drinkers, balancing bird density with ventilation capacity and using litter materials with high water-holding capacity.
In one study, the inclusion of soy hulls, wheat midds, or corn DDGS in diets for laying hen, has reduced the total ammonia emission and the rate of ammonia emission from manure by up to 50%. This result has been attributed here to a shift in the partitioning of nitrogen excretion from uric acid to microbial protein, and a reduction in manure pH stemming from an increased content of microbially produced volatile fatty acids, causing a shift from ammonia (NH3) to the more water soluble ammonium (NH4), thereby reducing ammonia emission.
Feed processing can impact nutrient availability and gas emissions. For example, fine grinding of feed increases the grain particle surface area, allowing digestive enzymes to breakdown the feed more easily and increase nutrient utilisation. Decreasing feed particle size from 1,000 to 600 microns increases dry matter and nitrogen digestibility by 5%-12% and lowers the amount or nitrogen in manure by 20%-24%. Excessive grinding, however, should be avoided as it causes gut motility and health problems.
Processing of feed into uniform durable pellets also affords significant benefits. The pelleting process increases the bulk density and reduces the segregation and dustiness of the feed, thereby reducing the losses during handling, transportation, and storage. Feed conversion efficiency is much improved when birds consume pelleted rather than mash feed because it results in less feed spillage during consumption. Moreover the heat treatment associated with pelleting improves feed digestibility by deactivating anti-nutritional factors and hence improves performance.
There are some additives that can be added to the diet to sequester ammonia or trap it. Among these additives is zeolite, a type of mineral with a porous or lattice-like structure, when included in the diet, binds ammonia in the faeces and prevents it from being emitted into the air.
Also, acidification of the diet may help alleviate the ammonia production problem. This can be achieved by adding gypsum (CaSO4) or calcium benzoate, or by lowering the dietary electrolyte balance. The acidic diet will result in acidic manure, causing ammonia (NH3) to be converted to ammonium (NH4), which is more water-soluble and not readily emitted into the air.
Another way to alleviate the ammonia production problem is to prevent uricase activity in the micro-flora in poultry manure. Egg yolk antibodies are economic alternatives for administering in feed to poultry. In order to use this dietary strategy effectively, a well balanced feed formulation and a more practical way of delivering the antibodies in feed remains to be developed.
Phase feeding allows producers to formulate diets to more closely meet the bird's amino acid and other nutrient requirements, thus reducing feed loss and nutrient excretion. In one study, the multiphase feeding reduced ammonia emission by 16%. In the past, such an approach has not been practical since most of the feed companies have not been able to produce more than four diets for broilers and six diets for turkey because of feed milling constraints. In recent years, however, some companies have been able to produce up to 17 different feed phases, thereby minimising nutrient deficiencies and excesses.
Minimising feed and water wastes
Poultry will waste a significant amount of feed if feeders are overfilled, adjusted too low, or poorly designed. In this case faecal N may increase by 1.5% for each 1% increase in feed waste, and ammonia emission rate will subsequently be increased. Feeders should, therefore, be designed in such a way that it is difficult for the birds to push the feed out of the feeders. In this way, the feeder height should be adjusted so that the top of the feed pan is level with the bird's neck, with the feed fill level to be adjusted to only 25% of the feeder pan.
Too much water in the house also results in excess ammonia emission and poor air quality. To alleviate the problem, the nipple drinker system should be adopted for better control over water intake and wastage. Also, excretion of wet droppings should be avoided. It has been found - for example - that diets containing drugs such as coccidiostats are associated with metabolic changes that are often associated with high water content of faeces. A change of feed ingredients will frequently overcome this problem. Such a dietary change may be made in a way which suits changes of activities of micro-flora present in the intestines during the course of medication.
As indicated earlier, dietary crude protein level should be reduced and the diet should be formulated based on amino acid requirements rather than crude protein. One extra benefit of reduced protein will be the reduced requirement for water intake, since excess protein requires water as part of the excretion process. If the protein level in the diet decreases by 3%, there will be an 8% reduction of water consumption. This, in turn, results in drier litter and consequently less moisture and ammonia in the air.