In addition,some organic P forms excreted in manure may displace sorbed inorganic and increase FIGURE 14.1 The soil–water phosphorus cycle.. Surface P applications will result in more P
Trang 1Environmental Pollution from Swine Production
A.L Sutton, B.T Richert, and B.C Joern
CONTENTS
14.1 Introduction 273
14.2 Environmental Impacts 274
14.3 Agronomic Considerations 275
14.3.1 Phosphorus 275
14.3.2 Nitrogen 277
14.4 Feed Formulation 279
14.4.1 Phosphorus 279
14.4.2 Nitrogen 280
14.4.3 Other Minerals 282
14.5 Feed Management 283
14.5.1 By-Product Feeds and Additives 283
14.6 Genetic Modifications 285
14.7 Odor Reduction 285
14.7.1 Nitrogen Manipulation 286
14.7.2 Adding Fermentable Carbohydrates 286
14.7.3 Microbial Manipulation 288
14.7.4 Physical Characteristics 288
14.8 Summary 289
References 290
14.1 INTRODUCTION
Nutrients, pathogens, and organic sources reaching our nations waters can adversely affect the tropic status and potential uses of the water body If nutrients from manures and other sources are applied at excessive rates to cropland, increased accumulations
of the nutrients in the soil can result in significant losses to bodies of water Gaseous emissions of volatile compounds from manure are also a threat to our atmosphere This chapter provides an overview of issues related to excess nitrogen and phospho-rus in the environment, and agronomic, dietary, and managerial practices that may
Trang 2be used to reduce nutrient and gas emission impacts on the environment and sustainenvironmental stewardship.
14.2 ENVIRONMENTAL IMPACTS
Nitrogen (N), phosphorus (P), and other nutrients are essential elements for normalgrowth, development, and reproduction of both plants and animals However, exces-sive nutrient levels, especially N and P, applied to cropland can potentially impairsurface water and groundwater quality It is well established that P is the limitingnutrient for phytoplankton production in lakes.1–3 Although fewer data exist forstreams and rivers, research indicates P also is a key element controlling productivity
in these systems.4,5 High P levels in surface waters accelerate the eutrophicationprocess and often result in the excessive production of phytoplankton such as algaeand cyanobacteria The respiration of these organisms leads to decreased oxygenlevels in bottom waters and, under certain circumstances (at night under calm, warmconditions), in surface waters.6 These decreased oxygen levels can lead to fish killsand significantly reduce aquatic organism diversity
Similarly N, especially in the ammonium form, can stress aquatic life at a verylow concentration and is toxic to fish at excessive levels The enrichment of N in waterwill enhance the biological degradation of organic matter resulting in algal growth andoxygen reduction in the waters Excessive NO3 levels in drinking water can causemethemoglobinemia in young infants7 and, at excessive concentrations, even in live-stock Ammonia emissions and gases created from digestion of manure slurry in pitsystems of confinement facilities can lead to nasal and lung irritation in workers caringfor livestock in these facilities Zhang et al.8 also reported that the air quality ofconfinement swine housing can have significant effects on respiration, as well as cause
an increase in white blood cell count of humans subjected to typical confinementconditions Pig manure contains a variety of organic compounds, complex to simple
in nature, inorganic compounds, including considerable amounts of N, P, Ca, K, Zn,
Cu, Cl, Mn, Mg, S, and Se, and indigenous microorganisms Fecal N arises fromundigested dietary protein, intestinal secretions (mucin, enzymes, etc.), sloughed intes-tinal cells, and intestinal bacteria Urinary N, largely in the form of urea, arises fromthe breakdown of absorbed dietary amino acids that are in excess of the amountsneeded for lean tissue protein synthesis and maintenance functions, and from thenormal turnover of body tissue proteins Most P excreted by pigs is in the feces Fecal
P arises from the dietary P that is undigested (mainly phytate) and/or unabsorbed, andfrom endogenous P secretions Normally, only small amounts of urinary P are excretedunless the diet is grossly excessive in P Other mineral concentrations in excreta depend
on their absorption, retention, and release after metabolism in the animal Currently
N and P are the major nutrients of primary environmental concern However, because
of performance enhancement, higher levels of Zn and Cu may be fed to pigs Thus,limiting Zn and Cu excretion also may become an important feeding practice tominimize their potential as environmental pollutants
Odors and gaseous compounds emitted from swine operations are a majordeterrent for the growth on the industry because of neighbor complaints, potentialhealth concerns, and deposition of particulates (acid rain) on the ecosystem Odorous
Trang 3and gaseous compounds are emitted from manure immediately after excretion due
to microbial metabolism in the digestive tract of the animal Further decompositionoccurs in storage, resulting in significant gaseous emissions and odors that have animpact on air quality These include nitrogenous and sulfur compounds, volatileorganic compounds, greenhouse gases (CH4, CO2, NOx), and particulates
14.3 AGRONOMIC CONSIDERATIONS
The soil-water P cycle is illustrated in Figure 14.1 Both organic and inorganic Pare present in soil, but only inorganic P is the form taken up by plants Soil Pdynamics are largely influenced by soil pH, clay content and mineralogy, amorphousiron and aluminum, and organic matter Inorganic P is the predominant P form inboth manures and commercial fertilizers Depending on soil pH and mineralogy,inorganic P can be sorbed on the surface of clays and amorphous iron and aluminumcompounds or precipitated as mineral salts until utilized by plants Organic forms
of P from crop residues, soil organic matter, and manures can be mineralized bysoil microorganisms and become available for plant uptake Conversely, inorganic
P can be immobilized to organic P forms not available for plant uptake In addition,some organic P forms excreted in manure may displace sorbed inorganic and increase
FIGURE 14.1 The soil–water phosphorus cycle.
Leaching and Drainage
P Removed with Crop
Surface Waters (Eutrophication)
Dissolution Precipitation
Dissolution
Plant Residue Uptake Plant
Trang 4inorganic P runoff and/or leaching in the soil Obviously, soil P cycling is a dynamicprocess The extent of P runoff from soils depends on rainfall intensity, soil type,topography, soil moisture content, crop cover, and the form, rate, timing, and method
of P application Surface P applications will result in more P runoff from soil thanincorporated P applications.9 Conservation best management practices that reducesurface runoff and erosion can greatly reduce the risk of P loss from soils.Much of the P reaching the receiving water is from runoff, often with sediment,from cropland receiving high rates of manure or inorganic fertilizers While P loss
to surface water and groundwater via P leaching through the soil profile is generallymuch smaller than runoff P losses, excessive P applications to soils over time willmove P to lower portions of the soil profile, and this P can discharge into tile drains,ditches, and eventually streams (Figure 14.1) Significant tile discharges of P alsocan occur via macropore transport of manure to tile lines after land application,especially during the dry season when cracks form in the topsoil Additionally, sandysoils with rapid drainage and low anion exchange sites generally have greater Pleaching potential than heavier textured clay-type soils
Swine manure N, P, and potassium (K) composition is not properly balancedfor plant uptake by typical crops grown in production agriculture The relativeratio of N, P2O5, and K2O in manure from pigs fed commercial diets after storage
in an under-floor liquid pit is approximately 1:1:1 When based on fertilizerrecommendations for N and crop removal rates for P2O5 and K2O, corn grainproduction requires roughly a 3:1:1 ratio, and if corn is grown for silage, thenapproximately a 2:1:2 ratio of N, P2O5, and K2O is required Therefore, if under-floor liquid pit manure is applied to meet the N requirement of corn grain pro-duction, manure P application will be approximately three times crop P removalunder an ideal manure application scenario Uncovered earthen pits and lagoonswill typically lose more N than under-floor pits, and if agitated prior to manureapplication, will have manure N:P2O5 ratios less than 1:1 Nitrogen losses forapplied manure that is not injected or immediately incorporated can be up to 30%10
within 4 days of application Additional N losses occur as the time between manureapplication and crop utilization increases In addition, excessive P levels in animaldiets increase animal manure P excretion, and land application of this manure tosoil can increase potential P losses from fields to surface water and groundwaterresources Ideally, if the ratio of N, P, and K in manure could be altered bynutritional means to more closely meet specific crop nutrient requirements, itwould alleviate a significant problem currently facing many pork producers uti-lizing manure as a crop nutrient resource
Current regulations are forcing pork producers to apply manure at agronomicrates based on the most limiting nutrient, which in most cases is P However, there
is the potential that producers can “bank” P for short periods of time if there issufficient land available to rotate the fields for manure application in subsequentyears A common practice may be to apply the manure to meet the N requirement
of the crop, but apply the manure to the field only every 3 years A rotation formanure application to crop fields must be established for manure applications tomeet crop P needs for the crop rotation grown on specific fields
Trang 514.3.2 N ITROGEN
The soil–water–atmosphere N cycle,11 presented in Figure 14.2, is only a part of theoverall N cycle Most soil N is sequestered in soil organic matter and only about1% of soil N is available to plants as nitrate (NO3) or exchangeable ammonium(NH4) at any one time Soil organic matter decomposition, manures, and commercialfertilizers are the primary inputs to the soil N cycle Organic nitrogen present inorganic matter, manures, and other organic N sources must be mineralized to ammo-nium (NH4) before it can be taken up by plants, held in an exchangeable form onsoil cation exchange sites, or fixed by various clay minerals If mineralization takesplace at the soil surface, ammonia volatilization can be a significant loss pathway.The ammonium fraction of manure also can be lost via ammonia volatilization ifmanure is left on the surface, especially under warm, windy conditions or if the soil
pH is greater than 7.0 During the normal crop growing season, solution andexchangeable NH4 is converted to NO3 fairly rapidly in the soil environment.Nitrate N may be taken up by plants, leached below the root zone, or lost to theatmosphere as NOx or N2 gas via denitrification Both nitric oxide and nitrous oxidegases contribute to greenhouse warming while nitric oxide also plays a role in theproduction of tropospheric ozone and is known to be the main component of acidrain.12 With the current interest in greenhouse gas emissions, gaseous N losses willlikely be more closely scrutinized and potentially subject to regulation in the future
FIGURE 14.2 The soil–water–atmospheric nitrogen cycle.
Trang 6Current agricultural practices in the Mississippi River Basin contribute imately 2.25 to 3.6 kg of nitrogen per agricultural hectare to the Mississippi Rivereach year Similar loss of nutrients is occurring in the livestock dense areas of Europe.Vitousek et al.12 report the rate of nitrogen deposition in the Netherlands is thehighest in the world at a rate averaging 40 to 90 kg⋅ha–1⋅yr–1 Timing and method
approx-of manure application can significantly affect potential N loss to the environment
In the midwestern U.S., much of the manure is applied in the fall and early winterwhen crops are either not present or not actively growing In general, the greaterthe length of time between manure application and crop uptake, the greater the risk
of N loss For fall applications of manure, cover crops can take up some N that mayotherwise leach or be denitrified during the winter and early spring prior to plantinggrain crops Timing of manure application is also important from the aspect ofcommercial fertilizer application as is reported by Torstensson and Aronsson.13
A comparison of N leaching from manure or commercial fertilizer applied toground covered with or without a catch crop was conducted in Sweden Catch cropsare fall planted crops, such as perennial ryegrass or winter rye used in this study,which serve as sources for nutrient uptake during manure application while thecommodity crop is not being grown The catch crop is then tilled back into the soiland the nutrients captured in the catch crop may be recycled back into the nutrientcycle for the next growing season The authors report that when either a single ordouble application of manure was applied to ground without a catch crop there was
a 15 and 34% increase in average N leaching, respectively, compared to commercialfertilizer application It was observed that while catch crops reduced N leachingfrom commercial fertilizer application 60%, when a double application of manurewas applied to a catch crop there was only a 35% reduction in leaching due to greaterapplications of mineral N in the spring with manured treatments compared to fer-tilized treatments
As is expected, ammonia release is subject to temperature as well as the mentioned time of manure application and other factors In a heavily concentratedswine and poultry production area in North Carolina, ammonia emission was directlycorrelated with air temperature and it was reported that as much as 50% of the totalamount of ammonia lost from swine effluent lagoons in a year is lost during summermonths.14 Robarge et al.14 suggest that because the partial pressure of ammoniaincreases with an increase in temperature and this leads to increased ammoniumions in the aqueous phase, the increased temperature during the summer monthswould cause greater deposition of ammonium ions in rain water and potentiallygreater deposition in alternative ecosystems
above-Nitrification inhibitors can aid in retaining fertilizer and manure N in the soiland minimize nitrate leaching by inhibiting the microbial conversion of ammonium
N to nitrate N Early research has shown that use of commercial nitrification itors will reduce nitrate leaching from injected swine slurry manure applicationswhen applied in the fall and summer seasons Varel15 showed that phosphoryl diamideand triamide compounds can be added to manure slurries and inhibit urease activityresulting in minimal volatile N losses Immediate injection of manure to croplandresults in <5% volatile N losses compared to 20 to 30% volatile N losses with surfaceapplication in a 48-h period after application.16
Trang 7inhib-14.4 FEED FORMULATION
Many feed ingredients in swine diets are high in phytate, and certain small grains(wheat, rye, triticale, and barley) contain endogenous phytase that can release thephytic P This creates a wide variation in the bioavailability of P in feed ingredients.For example, the P in corn is only 14% available while the P in wheat is 50%available.17 The P in dehulled soybean meal is more available than the P in cottonseedmeal (23 vs 1%), but neither source of P is as highly available as the P in meat andbone meal (90%), fishmeal (93%), or dicalcium phosphate (100%) Due to this greatvariation in the availability of P in feed ingredients coupled with a lack of preciseinformation on the requirements of P for pigs, nutritionists have great difficulty inestimating the available P levels in the diet Consequently, additional supplemental
P is added to the diet, oftentimes in excess for a safety margin and excess P isexcreted in manure Reducing the safety margin alone would potentially decrease Pinput by 8 to 10% in the diet and excretion by 20 to 30% (Table 14.1).18
Supplementing the diet with the enzyme, phytase, is an effective means of ing the breakdown of phytate P in the digestive tract and reducing the P excretion inthe feces Using phytase allows a lower P diet to be fed because a portion of theunavailable phytate P in the grain and soybean meal is made available by the phytaseenzyme to help meet the pig’s P needs Table 14.1 shows the theoretical model forusing dietary P levels and phytase supplementation on P excretion Numerous studieshave indicated that the inclusion of phytase increased the availability of P in a corn–soy-bean meal diet by threefold, from 15% up to 45%.19,20 Phosphorus excretion wasreduced from 31 to 62% when the diets for growing through finishing pigs werechanged with a lower inorganic P level and addition of phytase or wheat bran (10 to20% of the diet) compared to typical corn–soybean meal diets.21 The availability andutilization of amino acids and other trace minerals have been shown to increase in pig
increas-Theoretical Model of Effects of Dietary P Level and
Phytase Supplementation, 91-kg Pig
Trang 8studies with phytase supplementation resulting in lower excretion of elements such as
N, Zn, Cu, Mn, and Ca.22 Radcliffe et al.23 showed an increase in P and Ca digestibilitywith the addition of phytase in low P and low Ca diet Qian et al.24 showed thatmaintaining a relative narrow Ca:P ratio (1.2:1 vs 2:1) is critical with low P diets andwhen phytase is used In their study, performance and P and Ca digestibility werereduced with the wider ratio
Smith et al.25 and Baxter et al.26 showed that use of phytase and/or LPA corn willchange the form of P excreted with an increased percentage of water-soluble or solublereactive P (SRP) in the manure In the Smith et al.25 study, use of phytase in the dietreduced SRP by 22% There has been an environmental concern about increased SRP
in poultry manure and potentially in manure from pigs fed phytase, especially if surfaceapplied to cropland or grassland, since it has been shown to increase runoff potential.However, if incorporated in the soil, this impact was not a concern.9
If P is the limiting nutrient for land application, a 50% reduction in excreted P
by pigs would mean that pork producers would need 50% less land for manureapplication and minimize any potential impact on water quality Obviously, this willhave a major impact if environmental regulations are being proposed to regulateswine waste application on a P basis While the impact of reducing dietary P belowNRC requirements, utilizing exogenous phytase and more available P sources seemslike a partial solution, its impact on whole-body P including lean tissue mass andbone health as well as on other essential minerals still needs to be investigated Theavailable P requirements and mineral composition of today’s genetic lines of pigshas not been determined and must be researched to produce greater reductions of Pexcretion from diet manipulation in the future
In the review by Kerr,27 the impact of amino acid supplementation with low crudeprotein (CP) diets to reduce N excretion ranged from 3.2 to 62% depending on thesize of the pig, level of dietary CP reduction, and initial CP level in the control diet.The average reduction in N excretion per unit of dietary CP reduction was 8.4% Table14.2 shows the theoretical model for the impact of reducing dietary protein andsupplementing with amino acids in a 91-kg pig Sutton et al.28 showed that reducingthe CP level in corn–soybean meal growing–finishing diets by 3% (from 13 to 10%CP) and supplementing the diet with lysine, tryptophan, threonine, and methioninereduced ammonium and total N each in freshly excreted manure and stored manure
by 28 and 43%, respectively (Table 14.3 and Table 14.4) Hobbs et al.29 showed thatreducing the CP in practical diets from 21 to 14% CP plus synthetic amino acids ingrowing diets and from 19 to 13% CP plus synthetic amino acids in finishing dietsreduced N excretion by 40% and also reduced concentrations of a majority of odorants
in the slurry In a practical feeding study, Kay and Lee30 used the same diets andshowed 41% total reduction in slurry N output Reducing the intact CP content of thediet (generally soybean meal) and replacing it with crystalline lysine and corn willreduce N input to the diet by 13.2% In studies at Missouri31,32 the protein content ofdiets for early finishing barrows (50 to 80 kg) was reduced four percentage units (15.34
vs 11.43%) with the addition of lysine, threonine, tryptophan, and methionine with
Trang 9no differences in any performance criteria Pigs fed the control diet and those fed thelow-protein diet had similar carcass protein and fat, and N retention However, Nexcretion of pigs fed the low-protein diets was 38% lower (31.5 vs 51.2 g d–1) Resultsfrom late-finishing pigs (85 to 120 kg) demonstrated that an all corn diet supplementedwith lysine, threonine, tryptophan, methionine, isoleucine, and valine gave similar pigperformance with similar carcass protein and fat, and N retention.33,34 Nitrogen excre-tion was reduced 48% with the low-protein amino acid supplemented diet However,due to the cost of isoleucine and valine, addition of soybean meal to meet these aminoacids and the addition of lysine, threonine, tryptophan, and methionine would be morecost-effective and result in a 30 to 40% reduction of N excretion without affecting pigperformance.
Kendall et al.35 used a reduced CP (12.2% CP) corn–soy diet with syntheticlysine, methionine, tryptophan, and threonine fed to 27 kg pigs for 9 weeks andcompared to pigs fed a high CP corn–soy diet (16.7% CP) Slurry manure contents
Theoretical Model of the Effects of Reducing Dietary
Protein and Supplementing with Amino Acids on N
Excretion by 91-kg Finishing Pig a
Change in dietary costs, b $ kg –1 0 –$0.004 +$0.009
a Assumes an intake of 3.0 kg d –1 , a growth rate of 900g d –1
b Delivered prices used as of 6/1/04: Corn, $0.09 kg –1 ; SBM (48%), $0.302
kg –1 ; Choice White Grease, $0.364 kg –1 ; Dical Phos., $0.346 kg –1 ;
Lime-stone, $0.064 kg –1 ; Salt, $0.161 kg –1 ; Swine Vitamin Premix, $1.050 kg –1 ;
Swine Trace Mineral Premix, $0.706 kg –1 ; Se Premix, $0.273 kg –1 ; Tylan
40, $0.273 kg –1 ; Lysine-HCl, $3.226 kg –1 ; DL-Methionine, $3.043 kg –1 ;
Threonine, $3.391 kg –1 ; Tryptophan, $35 kg –1
Source: Adapted from Cromwell, G.L and Coffey, R.D., Proc Pork
Acad-emy, 1995, 39.
Trang 10had a lower pH (0.4 units), lower total N (40%), and lower ammonium N (20%)from pigs fed the reduced CP diet compared to the slurry manure from pigs fed thehigh CP diet.
Copper sulfate addition to the diet (125 to 250 ppm) has been shown to improvefeed efficiency 5 to 10% and to reduce odors36 but will significantly affect copperexcretion.37 Adding copper sulfate at 125 or 250 ppm to the diet will increase Cudietary input by 7.8 and 16.7 times a control diet (15 ppm of Cu), respectively Use
of lower levels of organic forms of Cu that provide similar growth promotion benefitsincreases the Cu excretion levels only 2.1 times the control Use of chelated minerals
or organic forms can reduce the excretion of a variety of minerals by 15 to nearly50% Researchers at Michigan State University and North Carolina State University38
TABLE 14.3 Effect of Diet on pH and Nitrogen
b TKN = total Kjeldahl nitrogen.
Source: Sutton, A.L., et al., J Anim Sci., 77, 430, 1999
TABLE 14.4 Effect of Diet on pH and Nitrogen
b TKN = total Kjeldahl nitrogen.
Source: Sutton, A.L., et al., J Anim Sci., 77, 430, 1999
Trang 11and enzymatic activities indicative of health parameters.
14.5 FEED MANAGEMENT
Diet ingredient sources, forms, and levels greatly influence nutrient availability andexcretion levels Understanding the bioavailability of nutrients from feed sources iscritical for formulating diets that will meet the productive needs of the animal withoutexcesses Any management procedure that improves the overall efficiency of feedutilization in a swine herd will generally reduce the total amount of manure produced,and should reduce nutrient excretion Controlling feed wastage improves herd feedconversion and reduces nutrient losses Use of wet–dry feeding systems will reducemanure volume by 30 to 50%; however, nutrient contents in the manure can increase
by about 30 to 50% Maintaining pigs under comfortable environmental conditionswith proper ventilation, temperature, humidity, space, and general well-being willimprove feed utilization and reduce nutrient excretions Raising genetically leanpigs, using growth promoters such as antibiotics, β-agonists, growth hormones,controlling diseases and parasites, and using good management practices are furtherexamples of how one can improve feed conversion efficiency and reduce nutrientexcretion by 10 to 15%
Fine grinding and pelleting are also effective in improving feed utilization anddecreasing dry matter (DM), N, P, and other mineral excretion By reducing theparticle size, the surface area of the grain particles is increased, allowing for greaterinteraction with digestive enzymes Hancock et al.,39 based on a summary of eightpelleting trials for swine, reported that pelleting resulted in an average 6% improve-ment in average daily gain and a 7% improvement in feed efficiency Wondra et al.40
reported a 23% decrease in DM excretion and a 22% decrease in N excretion whenfinishing diets were pelleted Henry and Dourmad41 reported for growing–finishingpigs that for each 0.1 percentage unit decrease in feed-to-gain ratio there was a 3%decrease in N output
Dividing the growth period into more phases with less spread in weight betweengroups allows producers to more closely meet the pig’s protein and other nutrientrequirements Also, since gilts require more protein than barrows, penning barrowsseparate from gilts will allow lower protein levels to be fed to barrows withoutcompromising leanness and performance efficiency in gilts.42 Henry and Dourmad43
reported that N excretion could be reduced approximately 15% when feeding of14% CP diet was initiated at 60 kg bodyweight, rather than the continuous feeding
of 16% CP grower diet to market weight A 14.7% reduction in urinary N excretionwas reported when a multiphase feeding program was compared to a two-phasefeeding program.44 Ammonia emission also was reduced 16.8%
By-product feeds can serve as a source of nutrients in pig diets Often, by-productfeeds, such as distiller’s grains, corn gluten meal, wheat middlings, etc., are included