environmental concerns about animal manure

A. W. Jongbloed and N. P. Lenis

Environmental concerns about animal manure

1998. 76:2641-2648. J Anim Sci

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1Presented at a symposium titled “Nutrient Management Proce-dures to Enhance Environmental Conditions” at the ASAS 89thAnnu. Mtg., July 1997, Nashville, TN.

2To whom correspondence should be addressed: phone: +31 320237 312; fax: +31 320 237 320; E-mail: [email protected].

Received October 6, 1997.Accepted May 26, 1998.

Environmental Concerns About Animal Manure1

A. W. Jongbloed2 and N. P. Lenis

Department of Nutrition of Pigs and Poultry, Institute for Animal Scienceand Health (ID-DLO), P.O. Box 65, Lelystad, 8200 AB The Netherlands

ABSTRACT: The structure of swine production haschanged dramatically in the last four decades. Rawmaterials for swine feeds are often grown in regionsother than where swine production takes place. Swinemanure is mostly spread in the neighborhood of thefacilities, which may lead to soil accumulation ofminerals such as P, Cu, and Zn. Moreover, soil nitratemay leach and result in enhanced nitrate levels inground and surface water. Large swine units generateodors, ammonia, and dust that can exceed tolerablelevels. Negative effects of swine production on the

environment have already led to new legislation thatlimits the use of animal manure or the expansion orlocalization of pig operations in some countries. Theconsequences of intensive swine production on theenvironment and possible solutions by means ofnutrition are outlined. Also, discussed are experiencesfrom the Dutch situation, forthcoming legislation, andenvironmental constraints on pig production in thefuture. Our approach centers more on the systemlevel.

Key Words: Pigs, Nutrition, Environment, Legislation, Ammonia, Emission

1998 American Society of Animal Science. All rights reserved. J. Anim. Sci. 1998. 76:2641–2648

Introduction

There is an increasing awareness of the impact thatlivestock production systems have on the environ-ment, especially in countries or regions with a denseanimal population (e.g., in The Netherlands; Jongb-loed and Henkens, 1996). In the past, animals werefed on farm-produced feeds, and the manure producedwas regarded as a scarce and valuable commodity formaintaining soil fertility. This ensured nutrient recy-cling except for losses associated with storage, trans-port, and nutrients deposited in milk and meat.Today, large confinement systems for livestock havebeen developed on limited acreage. However, despitethe advantages of animal production on a large scale,legislation in some countries and states limits the useof animal manure or the number of animals perhectare of cultivated land.

The aim of this paper is to describe the environmen-tal concerns associated with intensive animal produc-tion and to give insight into the Dutch legislation thatseeks to minimize environmental pollution. Examples

will be presented for nutritional means to reduce theexcretion of nitrogen and minerals. In addition,speculation on the future of pig farming from anenvironmental viewpoint is presented.

Environmental Concerns

Environmental concerns can be divided into threecategories, concerns related to the soil (accumulationof nutrients), the water (eutrophication), and the air(global warming, odors). The major thrust in TheNetherlands is finding an acceptable balance betweenthe input and output of N and minerals per hectare ofcultivated land. Some minerals, such as P, Cu, and Zn,accumulate in the soil and contribute via leaching andrun-off to eutrophication of ground and fresh watersources. Table 1 lists the contributions of phosphate(P2O5) from animal manure and fertilizers (CBS,1995). Considering that crops use an average of 50 kgof P2O5 per hectare, it is apparent that, in TheNetherlands, P accumulates in the soil. This leads toeutrophication and may cause excessive growth ofalgae, which sometimes results in massive fishmortality (Roland et al., 1993).

Because of excessive application of manure perhectare of land, heavy metals accumulate in the toplayer, with consequences for plant growth and poten-tial risks for human and animal health (e.g., copperintoxication of sheep; Henkens, 1975) and soil life


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JONGBLOED AND LENIS2642

Table 1. Amount of P2O5 in animal manure and fertilizers(kg/ha cultivated land; CBS, 1995)

Province/Country 1970 1980 1987 1990 1995

Noord Brabant 110 195 245 200 204Gelderland 115 170 200 175 162Limburg 110 165 215 160 174Netherlands (manure) 78 114 124 110 107Netherlands (fertilizer) 49 42 44 38 32Netherlands (total) 127 156 168 148 139

Table 2. Allowed application of P2O5 (kg/ha)from 1987 onwards in The Netherlands

Year(s) Grassland Arable land Corn silage

1990 and earlier 250 125 3501991−1993 200 125 2001994 200 125 1501995 150 110 1101996−1997 135 110 110

(earthworms, microbiology; Van Rhee, 1974). Fur-thermore, because of excessive application of manureand fertilizers per hectare of land, surplus precipita-tion and leaching of nitrate often exceed tolerablevalues in fresh water (50 mg nitrate/L). Similarly,the tolerated level of 12 mg of K per liter of freshwater is exceeded, although the environmental conse-quences of this are not clear at this time (VanBoheemen et al., 1991). Generally, the enrichment ofthe environment may lead to less biodiversity. Thisaspect is stressed more and more in The Netherlands.

Ammonia and greenhouse gases, together withnoxious odors from animal husbandry, are also ofconcern. The latter is regarded as a major concern inthe United States and Canada. Animal husbandrycauses 92% of the total NH3 emission in TheNetherlands (Heij and Schneider, 1995). The emis-sion of CH4 primarily from ruminants, and gases suchas N2O contribute to global warming (greenhouseeffect) by 15 to 20% and 6%, respectively (Leijen etal., 1993). Dust, noise, visual pollution, and animalsand their manure as carriers of pathogens may also beregarded as environmental concerns. Furthermore, theloss of organic matter in the soil predominantly as aresult of erosion may also be regarded as one of themajor environmental threats (Pimentel et al., 1995).

Legislation in The Netherlands

A disturbed mineral balance in several soils in TheNetherlands was recognized as early as the 1970s byseveral experts (Jongbloed and Henkens, 1996), butlegislation was not enforced until 1984.

1984 Legislation. Legislation was enforced in TheNetherlands to achieve 1) equilibrium in fertilizerapplication, 2) reduction of acid deposition, and 3)protection of surface and ground water quality. Withrespect to soil protection, the policy stated that in thelong term, no harm to plant growth or health risk forhumans and animals was permitted. In the same year,a freeze was placed on pig and poultry expansion.

Criteria formulated for N stated that the concentra-tion of nitrate in ground and surface water should notexceed 50 and 10 mg/L, respectively. Moreover,surface water should not contain more than .02 mg ofNH3 N per liter. Furthermore, NH3 emission should

be reduced by 50% in the year 2000, relative to 1980.From 1992, all manure pits should be covered. For P,the ground and surface water should not exceed .10mg of ortho-P per liter (about .15 mg of Pt per liter).Local authorities can further reduce the allowableconcentrations, especially when the farms are locatedclose to woods or natural parks.

The amount of animal manure that could be appliedper hectare of land was based on its P content (Table2). The allowed application was gradually reduced forall types of land, which resulted in an amount of 110kg of P2O5 for both arable land and land used for cornsilage and 135 kg for grassland. In order to reduceleaching of nitrate, application of manure on the fieldwas restricted more during the autumn and winter,when there is no growth of crops. The applicationperiod also depends on the soil type and crop.Additionally, restrictions were made with regard tothe method of application. More use of the injectionmethod or incorporation immediately after applicationwas enforced to reduce ammonia emission. If the P2O5production per hectare of cropland exceeded theamount allowed, the farmer had to pay a tax on thesurplus, which had to be transported to other regions.Manure transport can be facilitated by use of themanure bank program.

1998 Mineral Accounting System (MINAS) Legisla-tion. In January 1998, new MINAS legislation, whichcontains far-reaching amendments to earlier Dutchlegislation, was introduced. The most drastic policychange is the introduction of compulsory mineralinput and output registration for farms with morethan 2.5 livestock units (LU) per hectare, of whichthere are about 50,000 in The Netherlands. Thelegislation is aimed at reducing the mineral surpluses


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ENVIRONMENT AND ANIMAL MANURE 2643

Table 3. Standard losses or levy-free surpluses of P(kg P2O5/ha) and N (kg/ha) in The Netherlands

in the new 1998 Mineral AccountingSystem (MINAS) legislation

aDeposition and mineralization not included.

Grassland andarable land, Grassland, Arable land,

Year P Na Na

1998 40 300 1752000 35 275 1502002 30 250 1252005 25 200 1102008/2010 20 180 100

and to achieve an equilibrium in fertilizer application,which means having a good balance between inputand output and taking into account obligatory losses.Apart from phosphate, nitrogen is included in the newlegislation. The MINAS includes all animals to whichmanure legislation applies: cattle, pigs, chickens,turkeys, foxes, mink, goats, ducks, and rabbits. A levelof 2.5 LU is equal to the number of animals thatexcrete 102.5 kg of manure phosphate per year. Thismight be 2.5 dairy cattle, 13.9 growing pigs, fivebreeding sows with pigs, or 427 broilers. Nearly allpig, poultry, and other intensive farms exceed thelimit of 2.5 LU per hectare. After the year 2000, allfarms with livestock will have to participate inMINAS.

The farms exceeding 2.5 LU/ha must submit aminerals accounting each year. Farmers register howmany kilograms of phosphate and nitrogen enter thefarm and how many leave the farm. Main sources ofinput are, for instance, supply of animals, feed(compound), fertilizers, and animal manure fromother farms. Main items of output are discharge ofslaughter animals, milk, animal manure, and crops.Because it is never possible to exactly balance inputsand outputs, some minerals are always lost. Theregulation, therefore, prescribes a maximum allowableloss (standard losses or levy-free surpluses) forphosphate and nitrogen (Table 3). Levy-free sur-pluses per hectare for phosphate and nitrogen arestringent and will be lowered in increments. Levy-freesurplus for P for each hectare of arable land andgrassland will gradually decrease from 40 kg of P2O5per hectare in 1998 to 20 kg in the years 2008/2010.For grassland, the levy-free surplus for N willdecrease from 300 to 180 kg/ha. An evaluation will beheld in the year 2000, after which the standard lossesmay be changed. In addition to the standard losses perhectare, there is also a correction for nitrogen lossesper animal because of ammonia volatilization inlivestock housing. When drawing up a mineralsaccount, farmers may deduct the levy-free surplusesand the corrections from their minerals account.

With the implementation of MINAS, the surpluslevy from the 1984 legislation has become obsolete.

Instead, in 1998 and 1999 farmers whose nitrogen andphosphate losses exceed the maximum have to paylevies of US$ 1.25/kg for the first 10 kg of phosphatesurplus per hectare and US$ 5 for each successivekilogram. From the year 2000, these levies will beUS$ 2.50 and US$ 10, respectively. The levy for Nsurplus will be US$ .75·kg−1·ha−1. In addition, MINASparticipants will have to pay destination levies at afixed rate of US$ 200, though some form of discountmay be possible. For specialized pig and poultryfarmers, having no or little land, the main costs due toMINAS legislation will probably be costs for discharg-ing, sampling, and analyzing the manure. The costs ofselling manure to arable farms will depend on supplyand demand. The amounts of P2O5 and N in themanure will be very decisive; however, dischargingmanure from the farm probably will result in substan-tial costs.

Livestock farmers who are required to submit aminerals account according to MINAS have twooptions: 1) a specific account or 2) an estimatedaccount. A specific minerals account is an accurateregistration of the quantities of phosphate and Nentering and leaving the farm. Farmers should alsoconsider the additional costs for sampling, weighing,and administration. However, a specific account givesa more accurate picture of the mineral inputs andoutputs and is usually fairer than the current systemof manure accounting. An estimated account is sim-pler and less costly, but it is also less accurate andcarries more disadvantages than the specific method.The estimated account is a calculation based onofficial, fixed rates. These rates are used to calculatethe quantities of phosphate and N in manure andother fertilizers. Standard losses and N corrections arethen deducted from this amount. There is also a fixeddeduction for minerals output through crops. In theregulation, the official rates are deliberately higherthan the average real-life situation to encouragefarmers to choose in favor of specific accounting.

Small farms with no more than 3 LU and less than3 ha of land are not required to register their land andanimals. However, evidence of manure transportsmust be recorded. This category also includes smallhorticulture farms. Different rules apply for green-house horticulture.

Apart from the minerals accounting system, a set ofmeasures that has proved its effectiveness in the pastwill become applicable to all farms as a basic package.It contains the following measures: 1) a ban onspreading manure in autumn and winter (September1 to February 1) for leaching-prone grassland andarable land, and, for grassland not prone to leaching,starting on September 15; 2) when spreading manureto make use of techniques that keep ammoniaemission to a minimum; and 3) to cover manure storesbuilt after 1987.

It is not the government’s intention to chargefarmers as much as possible. The levies are meant as


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a stimulus for change. Farmers will often find thattaking the necessary measures is cheaper than payinglevies for surplus losses. The right measures will carryextra costs, such as selling manure. Other measurescan save money, such as reducing the use of inorganicfertilizers or concentrates. Dutch farmers are doubtfulthat a strong agriculture is possible under thesestringent standards. Farmer organizations have askedfor a more regional approach and, at a certain level,this will be allowed. If the environmental targetsprevail over the possibilities of good agriculturalpractice, then either high investments will be made orthe number of animals will be reduced. Possibly, newsolutions will come forward from research. Addition-ally, according to a new restructuring law, the totalnumber of pigs will be reduced by 20 to 25% betweenSeptember 1998 and the end of the year 2000.

Reduction of N and P Excretionby Pigs Through Nutrition

The Netherlands was the first country to initiate alarge research program to reduce the environmentalimpact of livestock production. Three main solutionswere proposed. The first one was a reduction ofmineral input via the feed. The second one was astimulation of practical solutions at the farm level,such as distribution and application of manure. Thethird solution was to upgrade manure by processingon a large scale for export purposes. In this section,only some general aspects of altering nutrition will bediscussed because details have been described else-where (Jongbloed and Lenis, 1992; Jongbloed andHenkens, 1996).

Nutritional research aimed at alleviating the ma-nure problem has focused mainly on reducing andimproving the efficiency of the dietary input of N andP. Growing pigs use only 30 to 35% of ingested dietaryN and P (Jongbloed and Lenis, 1992). For this reason,it is important to supply dietary N and P in closeaccordance with an animal’s requirement. This callsfor adequate knowledge about the digestibility ofamino acids (AA) and P in the feed, and on therequirement for these nutrients. It is possible toenhance the digestibility of P in feeds by usingextrinsic enzymes. In addition, the excretion of N andP can be reduced further by exchanging less-digestiblefeedstuffs with more-digestible ones. Also, by im-proved performance (improved genetic lines of pigs),the excretion of N and P can be substantially reduced.

Match Dietary N and P with Requirement. Two newevaluation systems were introduced. The one forprotein is based on requirements for the apparent ilealdigestibility of lysine, methionine, cystine, threonine,and tryptophan (Lenis, 1992; CVB, 1997). Data onthe ileal digestibility coefficients for some feedstuffsare provided in Table 4. For maximum growth

performance of growing-finishing pigs, the require-ments for ileally digestible methionine + cystine,threonine, and tryptophan relative to the ileallydigestible lysine should be 59, 60, and 19%, respec-tively (Lenis, 1992). Recently, this has been changedslightly, considering the increasing contribution formaintenance for the sulfur AA and threonine duringthe growing period (Lenis, 1996). Compared withcastrates, boars and fast-growing sows should receivea 10% higher amino acid supply. The optimum ratiobetween essential amino acid N and total N for Nutilization was between .45 and .55% of intake,depending on the level of daily N retention (Lenis etal., 1996). For N retention, this optimum ratio isslightly lower.

The total P content of a diet does not reflect itsnutritive value correctly. Therefore, we introduced anew evaluation system for P based on its apparentdigestibility. The large variation among and within afeedstuff is attributed to differences in phytate Pcontent, phytase activity, and processing (Jongbloedand Kemme, 1990). Also, the requirements for P areexpressed in terms of digestible P using a factorialmethod (Jongbloed et al., 1994). As we use a model,we can adapt the recommendations to the level andtype of production and the physiological status of theanimal. Because the required concentration of digesti-ble P/kg of feed decreases as live weight of the pigincreases, phase-feeding systems can be introduced toreduce P excretion.

Enhancement of Phosphorus Digestibility. The highexcretion of P by pigs is mainly because about two-thirds of P in feedstuffs from plant origin is present asphytate, the salt of phytic acid (Jongbloed, 1987).Phytate P is almost indigestible for pigs, which forcesfeed manufacturers and farmers to add inorganic P totheir feeds. In the presence of supplementary orintrinsic phytase, phytic acid can be hydrolyzed toliberate free orthophosphates and inositol for absorp-tion. When 500 to 1,000 units of Aspergillus nigerphytase is added per kilogram of feed, the increase inamount of digestible P is almost 50% of the require-ment for digestible P in a growing pig (Jongbloed etal., 1996). Also, several other types of microbialphytase have enhanced P digestibility substantially.Phytase-supplemented feeds for growing-finishing pigsand for pregnant sows may need little or no sup-plementary feed phosphate. Microbial phytase iscommercially available and has been incorporated inmore than 70% of pig feeds in The Netherlands.

Changes in Feedstuff Composition. In order todecrease the excretion of P, feedstuffs should bechosen in which P is in a highly digestible form.Because feed phosphates are only used to supply P,one can easily choose those forms in which P is easilydigestible. In The Netherlands, this has already led toa total shift to monocalcium phosphates at theexpense of dicalcium phosphates.


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Table 4. Ileal digestibility of N and some amino acids (%) and apparent total tractdigestibility of P (%) in some feedstuffs (Jongbloed and Henkens, 1996)

Feedstuff N Lys Met Cys Thr Trp P

Maize 70 56 82 70 62 48 17Barley 73 70 80 71 66 73 39Peas 74 83 74 63 69 67 45Wheat middlings 69 71 76 69 63 74 28Soybean extracted 81 86 86 76 79 83 38Sunflower extracted 75 74 86 73 72 79 16Meat meal fat 73 83 85 55 78 74 80

For economic reasons, it is impossible to formulatediets without oversupplying certain AA, particularlywhen many by-products are used. Lowering theproportion of some by-products and other feedstuffswith a low ileal protein digestibility in the diet infavor of cereals and other feedstuffs with a higherprotein digestibility will result in a better balance ofdietary AA. Nitrogen excretion can be substantiallylowered by reducing the protein level by more thantwo percentage points. In doing so, feeds need to besupplemented with lysine, methionine, and, in mostcases, threonine and tryptophan. This reduction incrude protein decreases N excretion by 20%. Datafrom other experiments in several countries show thateven bigger reductions in dietary protein level arepossible with little effect on animal performance.

In addition to the changes mentioned before, thereis also the possibility of enhancing the energyconcentration in the feeds. As a result, feedstuffs thathave a higher digestibility are used, consequentlyleading to a lower excretion of N and minerals viafeces.

Current Status of Phosphorus and Nitrogen Excretionby Pigs in The Netherlands. Table 5 summarizes thechanges in P excretion by growing-finishing pigs inpractice in The Netherlands. From 1973 to 1996, thetotal P content in feeds for growing-finishing pigs hasdecreased by more than 2.5 g/kg, and the feedconversion ratio has improved substantially; thehealth of the pigs has not been impaired. Phosphorusexcretion has more than halved, whereas, with regardto N excretion, only a slight decrease has beenobserved.

Reduced Ammonia Emissionand Manure Volume

In a preceding discussion, it was shown that Dutchlegislation requires that NH3 emission from livestockproduction be lowered substantially. For growing-finishing pigs, it means that the NH3 emission per pigspace has to be reduced from 2.10 (half-slatted floor)to 1.38 kg.

Ammonia emission from pig manure originatesfrom urea in the urine. Nitrogen in the feces comprises

undigested dietary N, endogenous N, and microbial N,partly present in nucleic acids. As a result of theurease activity of fecal microbes, urea is rapidlyconverted into ammonia, which easily volatilizes.Factors that influence the rate of ammonia emissionare concentrations of urea and ammonia/ammoniumin the manure, air temperature and velocity, pH,emitting surface, and dry matter content (Van Vuurenand Jongbloed, 1994).

It is possible to reduce ammonia emission substan-tially by nutritional management aimed at reducingthe N and urea content in urine and slurry, loweringthe pH of urine and slurry, and reducing total Nexcretion by improvement of the utilization of dietaryprotein. The latter reduces the amount of urea and Nexcretion. This will result in a diminished emission ofammonia (Oldenburg and Heinrichs, 1996). RecentlyCanh et al. (1998) showed that for every percentageunit reduction of dietary CP ammonium concentrationwas reduced by approximately 11% and ammoniaemission by 10 to 12%. Because a surplus of slurry ona farm often has to be transported over a longdistance, more attention should be paid to increasingthe DM content of slurry. In this respect, not only theeffect of several minerals (i.e., Na, K , and Cl), butalso of protein, nonstarch polysaccharides, and struc-tural carbohydrates in the diet should be studied toreduce water intake by pigs (Mroz et al., 1995). Thelatter two may enhance satiety and, therefore, reducewater intake, whereas the minerals and proteinenhance water requirement.

In order to reduce ammonia emission, many meas-ures have been developed by changing the ratiobetween urinary N and fecal N (bacterially fermenta-ble carbohydrates); reducing urea degradation (sepa-ration of urine and feces and urease inhibitors);binding the ammonia (yucca extract and clay miner-als); lowering the slurry pH (acidification); reducingthe emitting surface by means of flushing, slopedfloors, and slurry removal (Van der Peet-Schwering etal., 1996), airtight storage, and soil injection. Somemeasures are still speculative and need furtherresearch.

Several authors have investigated the possibilitiesof reducing the ratio between urinary N and fecal N byincluding bacterially fermentable carbohydrates in the


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Table 5. Mean excretion of P and N of growing-finishing pigs from 25to 110 kg in The Netherlands (kg/pig; adapted from PDV, 1997)

aStarter diet/finisher diet.

In feed, g/kgFeed conversion

ratio

Excretion

Year P N P N

1973 7.4 23.8 3.37 1.62 4.741983 6.2 24.4 3.08 1.18 4.301988 6.0/5.0a 26.9 2.94 0.85 4.641992 5.5/4.9 26.9 2.86 0.77 4.461996 5.3/4.6 26.7 2.74 0.67 4.13

Table 6. Nitrogen balance (relative values, %)and ammonia emission using fermentable

carbohydrates (Bakker et al., 1996)

Treatment 1: basal diet 35%, cornstarch 65%; basal diet mainlyconsists of soybean meal.

Treatment 2: basal diet 35%, cornstarch 32.5%, raw potato starch32.5%.

Treatment 3: basal diet 35%, raw potato starch 65%.

Treatment

Item 1 2 3

Intake 100 100 100Feces 15 29 36Urine 49 32 32Retained 36 37 32NH3 emission, % 100 — 87

diet. Nitrogen incorporated in bacterial protein infeces is less easily degraded to ammonia than urea Nexcreted in urine. Microbial fermentation of DM in thehindgut can increase the excretion of N in feces, and itreduces the N excretion in the urine. Canh et al.(1997) reported an increase in fecal N as a proportionof total N excretion from 22 to 45% when 300 g/kgsugar beet pulp ( SBP) was included in the diet,compared with diets based on grain, tapioca, andoilseed cake. Ammonia emission during the 1st 7 dafter excretion, from slurry standardized at 7.5% DM,was 45% lower with the SBP diet. Bakker et al.(1996) showed that inclusion of raw potato starch( PS) in diets for growing pigs increased the amountsof DM disappearing from the hindgut, and less Ndisappeared from the hindgut (Table 6). With the PSdiet, there was a net N appearance in the hindgut.The N excretion in urine was lower with more PS inthe diets, but N retention was not different.

According to Canh et al. (1997), a lower slurry pHrelated to a higher VFA content and a lower dietarybase excess may also affect ammonia emission. Mrozet al. (1996) measured the effect of dietary cation-anion difference ( DCAD) and acidifying salts onurinary pH, nutrient retention, and indoor ammoniaemission by growing pigs (Table 7). They addedacidifying Ca salts to dietary Ca levels of 7 and 10 g/kg. Urinary pH was reduced by 1.6 to 1.8 units,thereby diminishing ammonia emission by 26 to 53%.In addition, reducing DCAD from 320 to 100 mEq/kgDM lowered urinary pH by .48 unit and ammoniaemission by 11%.

Dietary additions of urease inhibitors are claimedto increase N utilization, reduce urea degradation, andreduce ammonia volatilization (Easter et al., 1993).Certain extracts of the yucca plant are sometimesregarded as urease inhibitors, but their mode of actionrelies on binding or converting ammonia (Kemme etal., 1993). Headon and Walsh (1994) reported a 50 to70% reduction in ammonia concentration after 9 wk.In contrast, Kemme et al. (1993) reported small andinconsistent reductions in ammonia emission after a2-wk adaptation period at similar and higher dosagesof yucca extract. They concluded that for the Dutchpractice, inclusion in the diet does not provide arelevant contribution to ammonia reduction. Results

of the inclusion of other materials, such as clinoptilo-lite and clay minerals, on animal performance seemquite variable (perhaps because of a lower dietaryenergy content), whereas their effect on ammoniaemission is unclear (Easter et al., 1993; Krieger et al.,1993).

Future of Pig Production froman Environmental Viewpoint

At the interface of sustainable agriculture andswine production, Honeyman (1996) indicates fourlevels of issues: the farm, the rural community, thesociety or consuming public, and the ecosystem orenvironment. It may be speculated that in the futurepig production will have to deal with more constraintsthat are imposed from society. This may relate toanimal well-being and health, to quality of the animalproduct and production system, to utilization ofnutrients, and last, but not least, to the environment.Application of nutrients via manure and(or) chemicalfertilizers on the fields should be in close balance withthe uptake by the crop, with minor losses via leachingor volatilization/evaporation.

To reduce or even eliminate the emissions of gasesand dust from pig operations, animals have to be keptin well-insulated confinement systems. Therefore,


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Table 7. Effect of dietary cation-anion difference (DCAD) and Ca sourceon urinary pH and ammonia emission (Mroz et al., 1996)

DCAD, mEq/kg DM Ca source

Item 320 100 CO3 SO4 Benzoate Cl2

pH urine 7.34 6.75 7.05 5.44 5.25 5.39NH3 emission from manure, % 100 81 100 79 56 78

vented air has to be cleaned before leaving thebuilding, and cheap technological solutions are re-quired. Furthermore, the expired CO2 from the pigscan be reused in greenhouses for vegetable production.Considering that more than one-half of the energysupplied to pigs is converted to heat, vented air can beused for heating (heat pump) the pig houses (inmoderate climates) and(or) for greenhouses. Also,better insulation of the building will result in usingless fossil energy.

To reduce the surplus of minerals and N in a region,more recycling of kitchen wastes and of by-productsfrom the food-processing industry should be en-couraged. Development of technologies (enzymes,processing) to degrade fibrous raw materials mayfurther enhance the utilization of energy from thoseraw materials in pig feeding. In certain regions,manure processing (fermentation for methane produc-tion, manure separation, combustion) may be inevita-ble. The generated energy can be used on the farm orfor the power grid. In addition, pig house roofs cangenerate energy with photovoltaic cells. By furtherintegration in the whole production cycle, pig produc-tion can be an important link in the food productionchain.

Implications

The aim of governmental policy should be toachieve an equilibrium in fertilization, which meanshaving a good balance between input and output andtaking into account obligatory losses. Manure legisla-tion can help to achieve this, and legislation has beensuccesful in The Netherlands. Nutritional manage-ment can substantially contribute to reduction in Nand P excretion and ammonia emission by pighusbandry, and it should be further integrated withother disciplines. An approach more at the systemlevel should be emphasized.

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Canh, T. T., J. B. Schutte, A.J.A. Aarnink, D. J. Langhout, andM.W.A. Verstegen. 1998. Reduction of ammonia emission bylowering protein content in diets of growing-finishing pigs.IMAG-DLO/ILOB TNO Rep. No. I98-31085. Wageningen, TheNetherlands.

Canh, T. T., M.W.A. Verstegen, A.J.A. Aarnink, and J. W. Schrama.1997. Influence of dietary factors on nitrogen partitioning andcomposition of urine and feces of fattening pigs. J. Anim. Sci.75:700−706.

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Headon, D. R., and G. Walsh. 1994. Biological control of pollutants.In: D.J.A. Cole, J. Wiseman, and M. A. Varley (Ed.) Principlesof Pig Science. p 375. University Press, Nottingham, U.K.

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