Introduction

There are a number of options available to pork producers interested in reducing nutrient output in manure. The nutrients of prime concern are:

  • copper (Cu)
  • zinc (Zn)
  • nitrogen (N)
  • phosphorus (P).

Potassium (K) should also be considered as it affects the fertilizing value of manure. Nitrogen and P also represent two of the most expensive nutrients in a swine ration. Excretion of nutrients in swine manure can be substantially reduced by a number of strategies, depending on individual farm situations.

Most of these strategies are quite simple and can significantly affect the bottom line. The most promising and practical of these strategies focus on two main principles - minimizing input and maximizing the efficiency of utilization.

Copper and zinc

In general, Cu and Zn in pig diets are much higher than the minimum requirements for normal performance (i.e. 5-25 ppm Cu and 50-125 ppm Zn for the various classes of swine). These minerals act as growth promotants when included at levels much higher than minimum requirements.

In Canada, the federal Feeds Act limits the maximum level of Cu and Zn in the diet to 125 ppm and 500 ppm respectively, but in the U.S. much higher levels are common. In some countries, like the Netherlands, growth-promoting levels of Cu and Zn are no longer allowed in finisher pig diets due to the impact on the environment. As long as minimum requirement levels of Cu and Zn are maintained, the excretion of these minerals in pig manure is not a concern; the focus then switches to N and P excretion.

Mineral balances

Overall, approximately two-thirds of N and P intake is excreted in manure (Table 1). Starter pigs are slightly more efficient than sows. However, since grower-finisher pigs produce the majority of the manure on a typical farrow-to-finish operation, typical values for these operations would be similar to the values shown for grower-finisher pigs. This extremely low level of efficiency and between farm variability leaves room for decreasing mineral excretion by improving the efficiency of retention in the pig. Differences in the amount of minerals excreted with manure between farms can be attributed to various animal and feed factors. These include:

  • feed usage and feed wastage
  • the level and digestibility of amino acids and P in the various diets
  • the minimum amounts of N and P required by the pig for basic body functions (maintenance requirements)
  • the inefficiency of using amino acids and P that are supplied over maintenance but below maximum N and P retention in the pig's body
  • the balance of amino acids supplied in the diet vs. the balance of amino acids required
  • the rate of N and P retention in the pig's body

Given the large variation between farms and environmental pressures, the need to closely monitor N and P balances on individual pig units will increase. This can be best accomplished by closely monitoring the amount and composition of feeds or feed ingredients used, and the number and weight of animals removed from the farm.

In the Netherlands such a mineral bookkeeping system is obligatory for farms with more than 2.5 large animal units (about 10 growing-finishing pig places) per hectare of land and requires feed companies to provide statements regarding amounts of nutrients delivered to each farm. With this approach, the calculated nutrient balances are rather sensitive to initial and final nutrient inventories with feed and manure.

In Ontario this approach to calculating nutrient balances has been integrated into 2 computer programs used to accurately predict the excretion in manure of the minerals of concern (N, P, P) in environmental pollution. In one approach developed at the University of Guelph, N, P and P excretion in pig manure is calculated from the difference between the amounts of N, P, and P fed to the animals (based on amounts of various feeds used and the N, P, and P content in the various feeds) and the amounts of N, P, and P removed from the farm in animals (based on the number of pigs in each category, live and dead, removed from the farm). NMAN is a software tool developed by the Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA) that assists farmers in predicting nutrient generation, based on manure analysis or database values, and determining land base requirements for agronomic use of nutrients.

Tables 1. Typical mineral balances (kg/animal) on Dutch pig farmsfootnote i

Table 1.1. Growing pigs (25-106 kg live weight)
VariableNitrogenPhosphorusPotassium
Dietary levels (%)16.70*0.521.22
Intake (kg/pig)6.361.232.90
Excretion (kg/pig)4.480.832.73
Retention (kg/pig)1.880.400.17
Efficiency of retention (%)29.5032.506.00
Table 1.2. Sows, including nursing piglets
VariableNitrogenPhosphorusPotassium
Dietary levels (%)15.70*0.591.32
Intake (kg/sow/yr)27.576.5314.52
Excretion (kg/sow/yr)22.505.514.00
Retention (kg/sow/yr)5.071.030.52
Efficiency of retention (%)18.4015.83.60
Table 1.3. Starter pigs (9-25 kg live weight)
VariableNitrogenPhosphorusPotassium
Dietary levels (%)18.40*0.671.25
Intake (kg/pig)0.940.210.40
Excretion (kg/pig)0.560.130.36
Retention (kg/pig)0.380.080.04
Efficiency of retention (%)40.5039.4010.00

*Crude protein (N x 6.25) rather than N levels.

Source : Jongbloed, A.W. 1991. « Developments in the production and composition in manure from pigs and poultry » dans Mest & Milieu in 2000. Ed. Verkerk, H.A.C. Dienst Landbouwkundig Onderzoek, Wageningen, Pays-Bas (en néerlandais).

Lowering nitrogen and phosphorus excretion through nutrition

The 3 most expensive components of a swine ration are N (an important component of protein and amino acids), P and energy. Nitrogen and P are also the most critical contributors to pollution from swine manure so it is important to maximize the efficiency with which these nutrients are used. Excretion of N and P in swine manure can be substantially reduced by a number of strategies.

1. Improve feed efficiency

Improved productivity is the most obvious strategy for reducing nutrient excretion. In general, a better feed efficiency leads to a lower excretion of N and minerals. Improving feed conversion 0.25 units would reduce N excretion 5%-10%.

Over the past 20 years, the feed efficiency of pigs growing from 25 kg to market weight has gradually decreased from approximately 4.0 to less than 2.85 in top-producing herds. Since feed efficiency is the single most important factor that determines feed cost/pig, at a cost of $265/tonne, each 0.1 unit improvement in feed efficiency can also save $2/pig.

Reduce feed and water wastage

Although often overlooked, a significant amount of feed nutrients may end up in manure simply because they were not consumed by the pig. Poor feeder design, improperly adjusted feeders, and feed form can contribute to a major feed wastage problem that directly impacts on nutrient output. Research in this area estimates feed wastage can range from 2%-20%, with typical operations at 5%-6%.

In general, N and P in manure will increase by 1.5% for every 1% increase in feed waste. If there is a noticeable amount of feed on the floor, at least 10% is being wasted and, at $265/tonne, producers are losing over $6/pig. To limit feed wastage producers can feed pelleted rations, pay close attention to feeder design and adjust feeders properly.

A good general guideline is to manage feeders so that only 50% of the bottom of the feeder is covered. Water wastage does not affect the amount of nutrients excreted, but it adversely affects manure processing and increases manure volume and disposal costs. The new generations of nipple drinkers reduce water use compared to conventional nipple drinkers, which tend to be favourite play toys for pigs. Bowl or cup systems, although difficult to keep clean, also reduce water wastage. Wet-dry feeders and liquid feeding systems offer options for greater control over water use and the impact of water wastage on manure volumes.

Improve feed digestibility

Proper processing of feeds represents a very practical means to decrease nutrient excretion through improvements in feed digestibility. Pelleting of feeds has been estimated to improve feed efficiency through increased energy and protein digestibility by 6.6% and subsequently reduce N excretion by 5%. Particle size is an area where producers can significantly improve feed efficiency.

Research at Kansas State University indicates that for corn-based diets ranging in particle size from 1200-400 microns, there is a 1%-1.5% improvement in feed efficiency for every 100-micron reduction in average particle size. Kansas State University recommends an optimum particle size for pigs of 700-800 microns.

Other means to improve diet nutrient digestibility include using ingredients with highly digestible nutrients and using enzymes, especially phytase. Note that improving digestibility only improves nutrient utilization if total dietary nutrient intake is reduced.

Recent research at Prairie Swine Centre indicates that reducing particle size from 900-600 microns was effective in reducing fecal N by 11%, but not total N excretion. This is likely because feed intake was not reduced with decreasing particle size and excess digestible protein intake was broken down after absorption and excreted in urine.

Improve animal productivity

Pigs with improved lean growth potentials can have a better feed efficiency as a result of reduced fat tissue growth and higher carcass lean yield as compared to conventional pigs. Feed additives that promote lean tissue growth may also reduce excretion of N and P as a result of a better feed conversion compared to non-supplemented feeds.

In addition, improvement in the herd health status, or in the thermal environment to which pigs are exposed, will lead to improvements in feed efficiency and thus reductions in mineral excretion.

One experiment estimated that converting to a specific-pathogen-free herd health status can improve feed efficiency by as much as 10% and, as a result, decrease N excretion by 10%.

2. Phytase

The most important anti-nutritional factor in swine nutrition, as it relates to nutrient management, is phytate. The major ingredients in pig diets are seeds (cereal grains) or products from seeds (oilseed meal and grain byproducts). However, 60%-80% of the P in these feedstuffs is present in the form of phytate, a compound that pigs do not use well. Bioavailability estimates of P in corn and soybean meal for pigs range from 10%-30%.

This low availability of phytate P poses two problems for producers - the need to add inorganic P supplements to diets and the excretion of large amounts of P in the manure. Phytate P must be hydrolyzed by an enzyme - phytase - into inorganic P before it is available to pigs. Research shows that phytase added to the diet can improve P digestibility. As a result, the total P levels in the diet should be reduced to improve the efficiency of retention and reduce excretion of P into the environment by 25%-50% (Table 2).

In addition, feeds supplemented with phytase for grower-finisher pigs and for pregnant sows may need little or no supplementary feed phosphate. Currently, adding phytase does not appear to add more cost to the diet because it is offset by the savings associated with reducing P and Ca in the diet. Despite it being cost neutral, phytase use in Ontario remains at 20%-30% compared to 70% in Quebec.

Consider these points when including phytase in pig diets.

  • Different commercial products differ in the content of active phytase. Phytase units (PTU) can be used to compare different products using a standardized test.
  • The efficacy of phytase is not the same for all feed ingredients and diets. This is likely due to differences in the location that phytate is deposited within the seed, e.g. in the germ in corn and the aleurone layer in wheat.
  • Not all phytase products are stable when exposed to heat. During pelleting the temperature of the feed should not exceed 70-75°C when uncoated phytase is included. Check phytase activity in the complete, processed feed. Phytase products with higher heat stability are now commercially available.
  • Phytase not only increases the digestibility of P; it also increases the digestibility of Ca and other trace minerals tied to the phytate complex (Cu, Zn, etc.). Phytase can improve feed utilization (by 1%-2%) in starter and grower pigs by making other nutrients more available as well. This results in additional "value" of added phytase.
  • When determining the value of phytase, consider the effects of reducing the P and Ca levels in the diet. In particular, in high-energy diets where (expensive) fat is used, reducing mineral levels reduce the need to use fat as there is more "space" in the feed formula. This results in reduction of ingredient costs.
  • The Ca to P ratio in the diet affects the utilization of P; maintain these at low levels (1-1.25:1 total or 2-3:1 available).

3. Formulate based on nutrient availability

The bioavailability of N and P varies considerably from one feed ingredient to another (Table 3). The major reason for the inefficiency of P utilization in pigs is the poor digestibility/availability of P that is present in plant products, largely because much of the P in plants is in the phytate form. In contrast, the availability of P in animal and inorganic sources is much higher. For this simple reason, pig diets should be formulated on available/digestible, rather than total, nutrient basis.

Estimated excretion of nutrients by pigs without and with footnote ii

Assumptions for 113 kg Market Hog (birth to 113 kg):

  • 306 kg of feed/pig
  • 88% DM, 16.5% CP (2.64% N), 0.55% total P in diet
  • 85% DM digestibility, 38% N retention, 38% P retention

Excretion per Market Hog:

  • 40 kg DM [306 x 0.88 x (1 - 0.85 = 0.15)]
  • 5 kg N [306 x 0.0264 x (1 - 0.38 = 0.62)]
  • 1 kg P [306 x 0.0055 x (1 - 0.38 = 0.62)]

Excretion for Hogs Marketed in Ontario (5.33 million in 2003):

  • 1.63 million metric tonnes of feed fed, 213,200 metric tonnes of DM excreted
  • 26,650 metric tonnes N and 5330 metric tonnes P excreted

Phytase Feeding and Reduction in P Fed:

  • A 0.1% unit reduction of P fed and the feeding of 500 units/kg of microbial phytase would result in 1630 metric tonnes less P excreted (1.63 million metric tonnes x 0.1%) or a 31% reduction in P excreted

Tables 2. Bioavailability of nitrogen and phosphorus in feed ingredients for pigs.footnote iii

Table 2.1. Cereal Grains
FeedstuffBioavailability P* (%)Bioavailability N** (%)
Corn14%78%
Oats22%76%
Barley30%79%
Triticale46%81%
Wheat50%81%
Table 2.2. Grain by-products
FeedstuffBioavailability P* (%)Bioavailability N** (%)
Oat groats13%79%
Corn gluten meal15%80%
Rice bran25%78%
Wheat bran29%71%
Brewers grains34%82%
Wheat middlings41%89%
Corn gluten feed59%66%
Distillers grains77%75%
Table 2.3. High protein meals - plant
FeedstuffBioavailability P* (%)Bioavailability N** (%)
Canola meal21%78%
Soybean meal, dehulled23%90%
Soybean meal, 44% protein31%89%
Table 2.4. High protein meals - animal
FeedstuffBioavailability P* (%)Bioavailability N** (%)
Feather meal31%67%
Meat and bone meal90%80%
Dried skim milk91%93%
Blood meal92%94%
Fish meal94%95%
Dried whey91%87%
Table 2.5. Inorganic phosphates
FeedstuffBioavailability P* (%)Bioavailability N** (%)
Steamed bone meal85%-
Defluorinated phosphate90%-
Monocalcium phosphate100%-
Diacalcium phosphate100%-
Table 2.6. Miscellaneous
FeedstuffBioavailability P* (%)Bioavailability N** (%)
Alfalfa meal100%56%

*Relative to the availability of P in monosodium/monocalcium phosphate which equal 100

**True ileal digestibility of lysine

Table 3. Effect of phase feeding on nitrogen excretion in grower-finisher pigs
ItemOne feedTwo feeds - growerTwo feeds - finisherTwo feeds - overall
Protein (%)16.0016.5014.0014.88
Feed:gain2.85--2.82
Feed intake (kg)257.0089.00165.00254.00
N intake (kg)6.572.353.706.05
N retention (kg)2.30--2.30
N excreted (kg)4.27--3.75
N excreted (%)65.00--62.00
% improvement---12.00

Variation in nutritional value of feed ingredients is an economic and environmental concern. Without complete and timely ingredient analysis there is a tendency for manufacturers to over-formulate rations resulting in higher ration costs and increased potential for nutrient losses. Using book values (such as those available from the National Research Council) for feed formulation will not be sufficient in the future.

As farmers strive to feed pigs more closely to their requirements, it will become increasing important that techniques are available to determine both nutrient levels and availabilities. Using near infrared reflectance (NIR) technology or other rapid nutrient analysis methods prior to mixing feed could allow for "real-time" feed formulation and significantly reduce safety margins of nutrients. Feed ingredients vary considerably in their nutrient content across ingredients and also within a single feed ingredient.

When researchers at the University of Guelph analyzed the P and phytate levels in Ontario corn and soybeans they found large differences depending on variety, location, and growing conditions. In corn, total P content ranged from 0.22%-0.42% while phytate levels varied from 48%-90% of total P. In soybeans, total P levels varied from 0.36%-0.84% with the percent as phytate from 43%-71%. Unfortunately, at the present time, there is no quick commercially available method to routinely determine phytate levels.

4. Match supply of available nutrients to requirements

The key to minimizing nutrient output is by feeding animals according to their nutrient requirements. Over- or underfeeding nutrients relative to the animal's requirement will increase output since animals will simply excrete all of the nutrients they are unable to use for maintenance and growth.

Accurate estimates of nutrient requirements are essential to optimize the production system but they are a moving target, depending on factors such as energy density of the diet, stage of development, genetic potential, sex, environmental temperature and health status. Since nutrient requirements and the optimum dietary nutrient levels differ between individual pig units, the main determinants of nutrient requirements may be monitored on individual pig units. In grower-finisher pigs, estimates of feed intake and lean tissue growth will provide good information for nutritionists to establish target diet nutrient levels.

Phase feeding

As the liveweight of a pig increases from 30-110 kg, the optimum concentration of amino acids and P in the feed decreases. So, introducing one or more additional feed(s) for grower-finisher pigs will help balance the amino acids and digestible P in the diet to the requirements of the animal; therefore less N and P is excreted (Figure 1).

When diets are precisely formulated to meet the protein and amino acid requirements of pigs, N excretion is reduced due to decreased dietary excess and improved utilization of nutrients. Calculations show that by changing from one feed system (common in Ontario) to a 2-phase system, the N needs would be met more precisely resulting in a reduction in N in manure of 12% (Table 4).

Producers who go from a single ration to 2 phases in the grower-finisher barn can expect to save $2/pig, with half that benefit at each additional step. Going from a 1-phase to a 3-phase feeding program should reduce N excretion by about 17.5%. Clearly, the incremental benefit of implementing one additional diet in a phase feeding program is smaller as the number of diets in the phase feeding program is increased.

Effect of number of feed phases on nutrient excess relative to nutrient requirement
Figure 1. Effect of number of feed phases on nutrient excess relative to nutrient requirement.

Accessible image description of Figure 1

Split-sex feeding

Feeding barrows and gilts separately can also decrease excretion of N and P. It is well known that barrows eat more feed, grow faster, are less feed efficient and yield lower carcass lean than gilts. Although there is little difference between barrows and gilts up to 25 kg, differences in feed intake and growth rate may be as high as 15% during the finisher phase.

Because they eat less feed and have a higher lean growth rate, gilts require higher levels of amino acids and other nutrients than barrows. Different diets can be fed to more closely match the nutrient requirements of the separate sexes, resulting in savings of $1/pig, while limiting excesses and reducing excretion.

5. Replace protein with synthetic amino acids

Protein is an expensive nutrient in pig diets, so maximizing the efficiency of protein and amino acid utilization is important. Diets containing amino acids at minimum requirement (for maximum lean growth) with minimal excesses is critical.

An experiment using chemically defined diets containing amino acids as a sole source of dietary N, showed that, with a near perfect amino acid balance, a 15 kg pig is capable of converting 87% of its absorbed N above maintenance to body protein. This does not mean that each of the 23 amino acids found in dietary protein are used at 87% efficiency for protein (some are used more efficiently, others less). Feed ingredients are combined to meet the pig's requirements for the most limiting amino acid. As a result, the protein content of the diet is higher than required because of the presence of excess amino acids.

For grower-finisher pigs, the greatest improvements in the efficiency of N utilization can be achieved from improving the dietary amino acid balance, so that the diet more closely reflects the true balance in which amino acids are required. Through manipulation of the dietary amino acid balance, N excretion in manure can be substantially reduced, by 35% in grower pigs and 20% in finisher pigs, without affecting animal performance.

In a simple example, N excretion can be decreased by approximately 15% when a 16% protein grower diet is replaced by a 14% protein finisher diet at 60 kg. Synthetic amino acids are commonly added to swine diets. L-Lysine-HCL is the most commonly used, and DL-methionine is used in some diets. Recently, synthetic L-threonine and L-tryptophan have become commercially available.

The ability of the swine industry to efficiently use competitively priced synthetic amino acids is limited by our knowledge of amino acid requirements of pigs and of biological availability of amino acids in feed. The order in which amino acids become limiting will vary with pig body weight, body protein gain and feeding level.

With the current cost of synthetic amino acids, it does not make sense to include synthetic amino acids other than lysine in grower pig diets but this will change as the availability and price of other amino acids improves.

Conclusions

Through science-based nutritional strategies, the mineral balance on pig farms can be substantially improved. Most of these strategies are quite simple to implement and can have a significant impact on nutrient output (Table 5) and the operation's profitability.

The most promising and practical of these strategies focus on two main principles - minimizing input and maximizing the efficiency of utilization. Using phytase, replacing protein with synthetic amino acids, and by feeding more closely to the animal's requirements, N and P excretion in pig manure can be reduced by up to 50%.

Applying nutritional strategies to reduce mineral excretion will increase the need for precise feed ingredient evaluation, feed formulation, manufacturing and delivery. Reducing water wastage from drinkers can also affect manure volumes.

Table 4. Potential impact of nutritional strategies on excretion of nitrogen and phosphorus
Strategy usedReduction in nutrient excretion
Improve feed efficiency3% for every 0.1 unit in improvement
Minimize feed wastage1.5% for all nutrients for every 1% reduction
Match nutrient requirements6-15% for N and P
Phase feeding5-10% for N and P
Split-sex feeding5-8% for N
Phytase2-5% for N; 20-50% for P
Formulate on nutrient availability10% for N and P
Replace protein with amino acids9% for N for every 1% reduction in crude protein
Highly digestible feed ingredients5% for N and P
Pellet the ration5% for N and P
700-1000 micron particle size5% for N and P
Enzymes: cellulases, xylanases, etc.5% for N and P for appropriate diet
Growth promoting feed additives5% for all nutrients
Low-phytate corn25-50% for P

Sources

Van Heugten, E. and T. van Kempen. 2001. Understanding and applying nutrition concepts to reduce nutrient excretion in swine. North Carolina Cooperative Extension Service. pp. 1-15.

Ferket, P.R., E. van Heugten, T.A.T.G. van Kempen, and R. Angel. 2002. Nutritional strategies to reduce environmental emissions from nonruminants. J. Anim. Sci. 80 (E. Suppl. 2): E168-E182.

This factsheet was originally written by Greg Simpson - Swine Nutritionist, Ontario Ministry of Agriculture, Food and Rural Affairs and Kees de Lange - Department of Animal and Poultry Science, University of Guelph.

This factsheet was originally written by Greg Simpson - Swine Nutritionist, Ontario Ministry of Agriculture, Food and Rural Affairs and Kees de Lange - Department of Animal and Poultry Science, University of Guelph.

Accessible image description

Figure 1. Effect of number of feed phases on nutrient excess relative to nutrient requirement

Figure 1 demonstrates the above explanation. As the animal's weight increases, the excretion decreases in a continuous downward slope. However, with 5 phase and 2 phase feeding, the excretion decreases in levelled steps, each consecutive step being a balanced excretion of the nutrients. The 5 phase feeding has 5 steps, and the 2 phase feeding has 2 steps.