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Because the pig is the point source of manure production, altering the diet fed to the pig has the potential for influencing nutrient utilization and excretion.
Dietary influences affect nutrient excretion and air emission.
The amount of nutrients excreted is influenced by:
- amount of dietary nutrients that is consumed,
- the efficiency with which the dietary nutrient is used by the animal, and
- the interrelationships of nutrients. The amount of natural body losses also has an influence but little can be done to influence the amount of nutrient losses from normal body functions.
Nutrient intake (-) nutrients used (+) body losses (=) nutrients excreted
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Management strategies have the potential to reduce nutrient excretion by the pig.
Nutrient excretion can be reduced by:
- reducing the total nutrient consumption of the pig ,
- increasing the utilization of nutrients by the pig, or
- balancing the various nutrients in the diet.
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You can reduce total nutrient consumption while maintaining optimum growth.
Diets must be formulated to provide the exact nutrient needs of the animal while guarding against nutrient imbalance. Some formulations provide an excessive "margin of safety" by adding low cost ingredients that are excreted by the pig. Feed ingredients should be analyzed for variations in nutrient content and digestibility. Adding excessive levels of nutrients to the diet will result in an imbalance of the nutrient flow resulting in excessive excretions.
You can increase the utilization of nutrients by the pig.
Nutrient use is affected by the quality of the feed ingredients and the feed processing.
Environmental conditions while growing cereal grains and protein sources can affect the quality and amount of nutrients in feed ingredients. High quality feed ingredients and regular testing will increase the utilization.
Fine grinding and pelleting are effective in improving feed use and decreasing dry matter, as well as decreasing nitrogen, phosphorus, and other mineral excretion. The average particle size in the feed industry is 1,100 microns while the recommended particle size by nutritionists is 650 to 750 microns. A reduction from 1,100 microns (3/8 screen) to 700 microns (1/8 screen) will reduce manure excretion by approximately 20-25 %.
Decreasing particle size increases the energy costs of grinding, reduces the throughput of feed mills, causes bridging problems, and may increase incidences of stomach ulcers in pigs.
Natural and synthetic enzymes may increase digestibility. Cellulase, protease, and glucanase have shown to increase digestibility in diets.
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Results of an imbalanced diet.
There is a complex interaction among nutrients in normal adsorption and metabolic processes. Imbalances result in excessive excretion of nutrients.
Diet manipulation strategies have demonstrated the potential to reduce odors. Diet strategies include the:
- Reduction of protein levels by 3%
- Substitute synthetic amino acids
- Optimize nutrient use and energy balances
- Feeding low levels of cupric citrate
Since most odor compounds are produced from processes involving protein decomposition, reducing the protein in rations to a practical minimum should help reduce manure odor. Feeds with reductions in NH3-N and volatile fatty acid concentrations are found when feeding 3% less crude protein diets supplemented with essential synthetic amino acids. Synthetic amino acids reduce ammonia, hydrogen sulfide, and odor emissions from confinement facilities. The removal of sulfur trace mineral sources also reduced odorous gases.
Rations that provide balance of the carbon: nitrogen ratio and that regulate the nitrogen and sulfur compounds reduce odors and improve the environment for pigs and humans working in the facilities. Feeding trials have shown low levels of cupric citrate significantly reduce odor intensity and improve odor quality when compared to control diets.
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You can design a diet that balances available amino acid composition to meet the needs of the pig.
Diets that meet the amino acid requirements of pigs (NCR, 1998) without going beyond the requirements should be fed.
High protein diets are needed when:
- Pigs are of superior genetic quality or in high health conditions
- Diets include porcine somatotropin or β-agonists (ractopamine)
- Split-sex feeding of gilts
- Lactating sows are nursing large litters
Protein levels for growing and finishing diets can be reduced by 2% when the diet is supplemented with 0.15% lysine. This supplement reduced the N excretion by 20%. Additionally, when the dietary protein was reduced by 4% and supplemented with threonine, tryptophan, and methionine, N excretion was reduced by 34%. In all cases, it is important to calculate the costs of synthetic amino acids as a part of the diet decision.
Diets should provide a good balance of amino acids that meet the lysine requirement. These diets have lower dietary protein levels than when lower quality protein sources, such as cottonseed, are used. Some feed manufacture use computer-formulated "ideal protein" rations in which the amino acids closely match the needs of the pig. Balanced diets result in less nitrogen being excreted.
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Benefits of reducing dietary crude protein and supplementing with synthetic amino acids.
When the crude protein (CP) level in corn-soybean diets was reduced from 13% to 10% and supplemented with threonine, tryptophan, and methionine, the levels of ammonium and total N excretion were reduced by 40% and 42%, respectively.
When CP is reduced by 1% and supplemented with synthetic amino acids, the ammonia emission into the air will be reduced by 8-12%. Further, when CP is reduced from 19% to 13%, the NH3 emission in building air is reduced 47-59%, manure odors are reduced by 40-86%, and p-cresol is decreased by 43%.
In recent research, rations with a reduced crude protein and supplemental amino acids (12% v. 17%), found slurry manure had a lower pH (.4 units), lower total N (40%), and lower ammonium N (20%). Additionally, emissions of ammonia and hydrogen sulfide were reduced by 40% while total room air odors were reduced by 30%. However, growth rate and feed efficiency were reduced by 5% and back fat depth increased slightly (.13cm) compared with the 17% CP diet.
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Minerals are critical in comprehensive nutrient management planning.
Critical minerals are phosphorus (P), potassium (K), zinc (Zn), copper (Cu), selenium (Se), and the calcium:phosphorus ratio. Animals to be kept for breeding have different mineral requirements, particularly for calcium and phosphorus. Nutritionists traditionally recommend dietary minerals at the 110 to 200 percent of the NRC requirements but may not be necessary.
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Precautions should be observed when providing minerals in the diet.
Mineral forms should be incorporate using the highest bioavailability to reduce excessive excretion. Organic forms of minerals are believed to have higher bioavailability and different routes of adsorption than inorganic forms. Minerals fed in higher dietary concentrations than required will reduce the efficiency of adsorption. Mineral needs are high from birth to 100 pounds, decrease moderately until 200 pounds, and decrease further until market weight. Nutritionists traditionally recommend dietary minerals at 110 to 200 percent of the NRC requirements. Research demonstrated that reduced dietary Cu, Zn, Mn and Fe concentrations do not depress growth or alter feed efficiencies of market animals.
Phosphorus is a critical nutrient since its concentration in manure limits land application and its loss in streams causes degradation of water quality. A reduction of 50% in excreted P by pigs would mean that producers would need 50% less land for manure application. This has a major impact if environmental regulations are phosphorous-based.
About three-fourths of the phosphorus in cereal grains and oilseed meals occur as phytate and is not well digested by pigs. The use of phytase and reduction of inorganic P will reduce the P input in the diet by 20%. Corn genetically selected for low phytic acid P (LP) may reduce the P excretion from 20-50% while reducing the P excretion by 21%. HAP corn increased the utilization of P by 30% while reducing the excretion by 23%. When HAP and phytase were combined, P excretion was reduced by about 40%.
Preliminary research indicates a concern that the phosphorus from manipulated diets is more soluble and therefore potentially more susceptible to runoff.
Most swine diets contain adequate potassium (K) to meet the pig's need, but its accumulation in lagoon effluent and pasture grasses is a concern. High potassium in forages depresses the availability of magnesium for ruminants. Potassium concentrations in lagoon effluent may result in 11 to 14 pounds of potassium applied per acre.
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Feeding practices should be considered to improve nutrient management.
- Reducing feed waste will reduce the amount of nutrients in lagoons.
- Split-sex feeding reduces nutrients without compromising efficiency in gilts.
- Optimum feeding schedules improve feed efficiency.
- Wet-dry feeding.
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New technologies should be considered to improve nutrient management
- Genetically modified feeds, including High Available Phosphorus (HAP) corn, HAP Low Oleic Acid (LO) soybean meal, and nutridense corn have potential to enhance use of nutrients and reduce nutrient outputs.
- Growth enhanced diets resulted in reduced urinary N excretion, decreased manure output, and a shorter feeding duration than traditional diets. Producers need technical assistance to optimize the feeding of ractopamine, including the level fed, duration of use, and dietary lysine levels fed.
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