By Dr. Jerry Shurson, University of Minnesota Department of Animal Science
© 2019 Feedstuffs. Reprinted with permission from Vol. 91, No. 08, August 5, 2019
© 2019 Feedstuffs. Reprinted with permission from Vol. 91, No. 08, August 5, 2019
Swine diet formulation and feeding management are evolving into a new era of decision-making. Nutritionists are beginning to implement "precision nutrition" approaches to customize diet formulations and feeding programs designed for specific farm conditions to capture the greatest economic value in pork production.
In addition, critical decisions are also being made on selecting and using alternatives to growth-promoting antibiotics and selecting feed ingredient sources based on their relative biosecurity risks of introducing foreign animal diseases.
Another important consideration is that environmental sustainability has become a new megatrend in global agriculture, and large, multinational companies have begun implementing programs to source feed ingredients based not only on cost and nutritional value but also on their environmental impact to reduce the overall carbon footprint of pork production systems (Shurson, 2017).
Several researchers have begun conducting life-cycle assessments of the environmental impacts of using various feed ingredients in animal feeds. However, the assumptions, breadth and scope of many of these assessments vary among studies and affect the results and their interpretations (Zilberman, 2017). In fact, many of the published studies do not include the economic impact of environmental assessments; they use static instead of dynamic models and do not take into account the actual measured emission rates from feeding diets, which may generate misleading results.
Although estimates vary substantially, food animal production contributes about 18% of total greenhouse gas (GHG) emissions (carbon dioxide, methane, nitrous oxide) globally, which is primarily attributed to gastrointestinal fermentation of feed in animals and manure storage (Steinfeld et al., 2006).
In addition to minimizing GHG emissions and the carbon footprint, precision feeding programs must also focus on minimizing nutrient excretion as well as odor and gas emissions from confinement pork production facilities (Lu et al., 2017). Minimizing these negative environmental impacts are important because high nitrogen, phosphorus and trace mineral concentrations in manure applied to cropland can cause soil concentrations of these nutrients to exceed crop removal rates.
Nitrate can leach through soils and contaminate groundwater supplies and is considered to be a major pollution concern on livestock farms. Methane and nitrous oxide produced in manure contribute to GHG emissions, and volatilization of ammonia causes acid rain, which has detrimental effects on vegetation and trees. Furthermore, phosphorus can enter surface waters through soil erosion and increase the growth of algae and other aquatic plants, which reduces dissolved oxygen and can cause fish death.
In addition, soil accumulation of excessive trace minerals (e.g., copper and zinc) can increase the risk of toxicity of plants and microorganisms.
Lu et al. (2017) suggested several nutritional strategies that can be effective for minimizing excess nitrogen, phosphorus and trace mineral excretion in manure. First, formulate diets to accurately meet animals’ dietary amino acid, phosphorus and trace mineral requirements. Dietary crude protein levels can be reduced by using supplemental synthetic amino acids. Excess phosphorus excretion can be minimized by formulating swine diets on a digestible phosphorus basis and adding supplemental phytase.
Using multiple phase-feeding programs to adjust diet formulations more frequently as nutrient requirements change during the various stages of production can substantially minimize excess nutrient excretion in manure. Using highly bioavailable sources of phosphorus and trace minerals and avoiding excesses of these nutrients when formulating diets can minimize excess mineral content in manure. Effective feed additives such as enzymes, probiotics, prebiotics and others that improve nutrient utilization in animal feeds can also have measurable impacts on reducing production costs while also minimizing potential negative environmental impacts.
Due to the relatively high fiber content of DDGS, dry matter excretion is increased when feeding DDGS compared to corn/soybean meal diets without DDGS (Almeida and Stein, 2012). This produces a greater volume of manure, which may increase the need for manure storage capacity or more frequent manure removal from swine production facilities.
Nitrogen and phosphorus excretion. It is well documented that using crystal-line amino acids and phytase in swine diets improves nutrient utilization efficiency and reduces diet cost, nitrogen and phosphorus excretion in manure and emissions of gases such as ammonia.
Kebreab et al. (2016) compared the impact of adding crystalline amino ac ids and phytase to swine diets in Europe, North America and South America. Their results showed that using these supplements in pig diets reduced GHG emissions by 56% in Europe, 17% in North America and 33% in South America versus feeding diets without supplemental synthetic amino acids and phytase. These are substantial reductions, and it is interesting to note that the North American swine diets used in this comparison contained 14.6% DDGS, but DDGS was not included in European and South American diets. As a result, the use of DDGS in swine diets can be part of the solution for minimizing the negative environmental impacts of pork production.
McDonnell et al. (2011) evaluated the effects of adding 0%, 10%, 20% or 30% corn DDGS to replace wheat in wheat- and barley-based diets — formulated on a net energy, ileal digestible amino acid and digestible phosphorus basis — on the nitrogen and phosphorus balance of growing/finishing pigs. As expected, nitrogen intake as well as urinary and total nitrogen excretion increased linearly with increasing DDGS levels in the diets (Table 1).
This was due to feeding excess nitrogen from DDGS relative to pig requirements, resulting in increased deamination of excess amino acids and increased urinary nitrogen excretion. Nitrogen retention was not affected by feeding the 10% and 20% DDGS diets, but feeding the 30% DDGS diet decreased nitrogen retention relative to nitrogen intake.
The increased nitrogen excretion commonly observed by feeding DDGS diets to swine can be minimized by using synthetic amino acids to reduce the amount of excess protein (nitrogen) in the diet.
In contrast, phosphorus intake linearly increased with increasing dietary DDGS levels, but there was no effect on phosphorus excretion or retention. These results indicate that feeding diets containing up to 30% DDGS increases nitrogen excretion but has no effect on phosphorus excretion in growing/finishing pigs when diets are formulated on a digestible amino acid and phosphorus basis.
Baker et al. (2013) compared the phosphorus balance and digestibility between dicalcium phosphate and DDGS in growing pigs and showed that although the standardized total tract digestibility (STTD) of phosphorus in DDGS was less than dicalcium phosphate, it was quite high (93% and 63%, respectively) and did result in greater fecal phosphorus excretion than dicalcium phosphate (Table 2).
However, because of the relatively high phosphorus digestibility in DDGS, diet inclusion rates may need to be reduced to minimize excess phosphorus excretion in manure. Furthermore, dicalcium phosphate is a much more expensive source of phosphorus in animal feeds, and global supplies of inorganic phosphate reserves are rapidly declining, which makes DDGS an excellent and more sustainable alternative phosphorus source in swine diets.
The addition of microbial phytase to swine diets has become a common practice to improve phosphorus digestibility, reduce phosphorus excretion in manure and lower diet costs by reducing the amount of inorganic phosphate required in the diet. Almeida and Stein (2012) added increasing levels of microbial phytase (0, 500, 1,000 or 1,599 phytase units [FTUs]) to corn or 50% DDGS diets and showed a linear improvement in STTD of phosphorus in corn (40.9%, 67.5%, 64.5% and 74.9%, respectively), and phosphorus digestibility tended to increase in DDGS diets (76.9%, 82.9%, 82.5% and 83.0%, respectively).
However, the magnitude of improvement in phosphorus digestibility by adding phytase to DDGS diets was much less than observed for corn and may not justify the additional cost of adding high amounts of phytase to swine DDGS diets.
Rojas et al. (2013) compared the phosphorus balance and digestibility of feeding growing pigs corn, DDGS and corn gluten meal with or without 600 FTUs/ kg of diet. Total phosphorus excretion was greatest for pigs fed the corn diet without phytase supplementation but was reduced by 50% when phytase was added (Table 3). However, feeding DDGS without phytase resulted in 40% less phosphorus excretion than feeding corn without phytase, and feeding corn gluten meal without phytase resulted in a 60% reduction in phosphorus excretion compared to feeding corn.
Adding phytase to the corn diet had the greatest magnitude of improvement on reducing phosphorus excretion, with no benefit in the DDGS diets and some improvement when phytase was added to the corn gluten meal diet. As a result, adding phytase to corn and corn gluten meal diets improves the STTD of phosphorus in corn and corn gluten meal but not DDGS.
This lack of response to adding phytase to DDGS diets is a result of the already high phosphorus digestibility that occurs from the degradation of phytate during the fermentation process in dry-grind ethanol plants. Therefore, formulating DDGS diets on a digestible phosphorus basis for swine can dramatically reduce phosphorus excretion in manure compared with feeding corn-based diets.
Several studies have been conducted to determine how feeding DDGS diets to swine affects gas and odor emissions from manure. Powers et al. (2009) measured air emissions of ammonia, hydrogen sulfide, methane and non-methane hydrocarbons when feeding growing/ finishing pigs diets containing 0% or 20% DDGS, with either supplemental inorganic or organic trace minerals. Although the organic trace mineral sources helped minimize the increased hydrogen sulfide emissions resulting from feeding the 20% DDGS diet, ammonia, methane and non-methane hydrocarbon emissions increased when feeding the DDGS diet. This is the only study that has shown an increase in ammonia and hydrogen sulfide emissions from feeding DDGS diets to pigs.
Spiehs et al. (2012) observed no differences when feeding a 20% DDGS diet compared with a corn/soybean meal diet to growing pigs over a 10-week period on total reduced sulfur, ammonia or odor concentrations.
Trabue et al. (2016) fed growing pigs diets containing 35% DDGS over a 42-day period and observed a reduction in manure pH and an increase in manure surface crust coverage, dry matter content and concentrations of carbon, nitrogen and sulfur in manure compared with pigs fed a corn/soybean meal diet (Table 4).
Warmer temperatures are often observed for manure with greater surface crusting or foam (van Weelden et al., 2015), which is associated with animals fed high-fiber diets (Misselbrook et al., 2005; Lynch et al., 2007; Wood et al., 2012) and lower pH (Kerr et al., 2006). As a result, the increased crusting of manure (Wood et al., 2012), higher temperature (Blunden and Aneja, 2008; Blunden et al., 2008; Rumsey and Aneja, 2014) and reduced pH associated with feeding DDGS diets can reduce gas emissions.
In fact, ammonia and hydrogen sulfide emissions from manure produced by pigs fed DDGS was less than from those fed a corn/soybean meal diet, but volatile fatty acid (VFA) and phenolic compound concentrations were greater in manure from pigs fed the DDGS diet (Table 4). It is likely that the increased crusting of manure from pigs fed the DDGS diet reduced hydrogen sulfide emissions by acting as a barrier for emission to the air.
Trabue et al. (2016) also measured emissions of various odor compounds from manure in the same study (Table 5). These data were normalized for pig weight (animal unit) and nutrients consumed. Pigs fed the corn/soybean meal diet had greater emissions of ammonia (53% of nitrogen consumed) and hydrogen sulfide (9% of sulfur consumed) than pigs fed the 35% DDGS diet (30% of nitrogen consumed and 2% of sulfur consumed).
These results are consistent with those from another study where ammonia emissions were reduced from feeding DDGS diets to swine (Li et al., 2011), which is likely due to the reduced pH of manure (Roberts et al., 2007) and increased microbial activity because more carbon is present in manure (Kerr et al, 2006; Ziemer et al., 2009).
However, manure from pigs fed the 35% DDGS diet had greater emissions of VFA and phenolic compounds, but there were no differences in indole emissions compared with manure from pigs fed the corn/soybean meal diet (Table 5). These differences were relatively small compared with ammonia and hydrogen sulfide emissions because total volatile organic compound emissions represented less than 1% of the total carbon consumed from feeding both diets.
Furthermore, human panelists detected no differences in the odor of com- pounds emitted from manure from pigs fed the two diets, but chemical analyses of individual odorous compounds showed greater hydrogen sulfide and ammonia and fewer total VFAs and phenols in manure emissions from pigs fed the corn/soybean meal diet than those fed the DDGS diet. The majority (60%) of odorous compounds in swine manure were derived from ammonia and hydrogen sulfide.
These data indicate that controlling nitrogen and sulfur excretion when feeding DDGS diets does not change ammonia and hydrogen sulfide emissions because the sulfur content in the DDGS diet was almost twice as high as in the corn/soybean meal diet (Trabue and Kerr, 2014), but manure hydrogen sulfide emissions from pigs fed the DDGS diet were about 30% less than those fed the corn/soybean meal diet.
Carbon dioxide, methane and nitrous oxide are major GHGs of concern in animal production systems. From the same study (Trabue et al., 2016), emissions of carbon, nitrogen and sulfur gases were also determined (Trabue and Kerr, 2014). Results showed that carbon dioxide, methane and nitrous oxide emissions, expressed on an animal unit and amount of element consumed basis, did not differ between the two diets (Table 6). However, as previously described, ammonia and hydrogen sulfide emissions were reduced by feeding the DDGS diet.
These results suggest that pigs fed DDGS diets have no greater GHG emissions from stored manure than those fed corn/soybean meal diets.
These results suggest that for swine farms installing biogas production systems to capture energy from manure, feeding DDGS diets would provide manure with significant amounts of carbon to generate greater amounts of methane than feeding corn/soybean meal diets.
A study by Thoma et al. (2011) showed about a 6% increase in the overall carbon footprint of pork production (production to consumption) when DDGS was included in swine diets. This increase was attributed to the additional energy consumed in processing corn during the ethanol and co-product production process compared with corn grain and soybean meal.
Mackenzie et al. (2016) use a more comprehensive LCA approach to determine the environmental impacts of using co-products from human food and biofuel supply chains in pig diets in Canadian pork production systems. As shown in Table 7, on a per kilogram of feed basis, feeding corn DDGS at maximum diet inclusion rates increased non-renewable resource use by 71%, non-renewable energy use by 68% and global warming potential by 30% compared with feeding the control corn/soybean meal diets.
However, including corn DDGS in the diets reduced acidification potential by 20% and eutrophication potential by 22% versus the corn/soybean meal and all other co-product diets. When environmental impacts were expressed on a kilogram of carcass weight basis, the impacts were less dramatic but went in the same direction as when expressed on a per kilogram of feed basis.
Due to the increasing interest in and importance of reducing the carbon footprint and resource use in pork production, more of these types of comparative studies will be conducted in the future.
Although DDGS is relatively high in protein and low in lysine and other amino acids relative to the pig’s requirements, the widespread availability and cost effectiveness of synthetic amino acids allows nutritionists to reduce dietary crude protein levels while meeting all of the essential amino acid requirements and reducing nitrogen excretion in manure.
One of the unique advantages of corn DDGS over other grains and grain-based ingredients is its relatively high total and digestible phosphorus content. Formulating swine and poultry diets on a digestible phosphorus basis and using phytase can significantly reduce manure phosphorus excretion. Furthermore, feeding DDGS diets to pigs does not appear to affect methane emissions but can substantially reduce ammonia and hydrogen sulfide emissions from swine manure.
Initial studies comparing DDGS with other co-product or byproduct ingredients indicate that feeding DDGS to pigs may reduce acidification and eutrophication potential by as much as 22% compared with corn/soybean meal and all other co-product diets.
In addition, critical decisions are also being made on selecting and using alternatives to growth-promoting antibiotics and selecting feed ingredient sources based on their relative biosecurity risks of introducing foreign animal diseases.
Another important consideration is that environmental sustainability has become a new megatrend in global agriculture, and large, multinational companies have begun implementing programs to source feed ingredients based not only on cost and nutritional value but also on their environmental impact to reduce the overall carbon footprint of pork production systems (Shurson, 2017).
Several researchers have begun conducting life-cycle assessments of the environmental impacts of using various feed ingredients in animal feeds. However, the assumptions, breadth and scope of many of these assessments vary among studies and affect the results and their interpretations (Zilberman, 2017). In fact, many of the published studies do not include the economic impact of environmental assessments; they use static instead of dynamic models and do not take into account the actual measured emission rates from feeding diets, which may generate misleading results.
Although estimates vary substantially, food animal production contributes about 18% of total greenhouse gas (GHG) emissions (carbon dioxide, methane, nitrous oxide) globally, which is primarily attributed to gastrointestinal fermentation of feed in animals and manure storage (Steinfeld et al., 2006).
In addition to minimizing GHG emissions and the carbon footprint, precision feeding programs must also focus on minimizing nutrient excretion as well as odor and gas emissions from confinement pork production facilities (Lu et al., 2017). Minimizing these negative environmental impacts are important because high nitrogen, phosphorus and trace mineral concentrations in manure applied to cropland can cause soil concentrations of these nutrients to exceed crop removal rates.
Nitrate can leach through soils and contaminate groundwater supplies and is considered to be a major pollution concern on livestock farms. Methane and nitrous oxide produced in manure contribute to GHG emissions, and volatilization of ammonia causes acid rain, which has detrimental effects on vegetation and trees. Furthermore, phosphorus can enter surface waters through soil erosion and increase the growth of algae and other aquatic plants, which reduces dissolved oxygen and can cause fish death.
In addition, soil accumulation of excessive trace minerals (e.g., copper and zinc) can increase the risk of toxicity of plants and microorganisms.
Lu et al. (2017) suggested several nutritional strategies that can be effective for minimizing excess nitrogen, phosphorus and trace mineral excretion in manure. First, formulate diets to accurately meet animals’ dietary amino acid, phosphorus and trace mineral requirements. Dietary crude protein levels can be reduced by using supplemental synthetic amino acids. Excess phosphorus excretion can be minimized by formulating swine diets on a digestible phosphorus basis and adding supplemental phytase.
Using multiple phase-feeding programs to adjust diet formulations more frequently as nutrient requirements change during the various stages of production can substantially minimize excess nutrient excretion in manure. Using highly bioavailable sources of phosphorus and trace minerals and avoiding excesses of these nutrients when formulating diets can minimize excess mineral content in manure. Effective feed additives such as enzymes, probiotics, prebiotics and others that improve nutrient utilization in animal feeds can also have measurable impacts on reducing production costs while also minimizing potential negative environmental impacts.
Manure volume, nutrients
Manure volume. Swine diets containing dried distillers grains plus solubles (DDGS) have higher fiber, crude protein and sulfur than traditional corn/soybean meal diets (Kerr et al., 2008; Zhang, 2010), which affects nutrient digestibility and excretion (Kerr et al., 2003; Degen et al., 2007; Kil et al., 2010; Anderson et al., 2012).Due to the relatively high fiber content of DDGS, dry matter excretion is increased when feeding DDGS compared to corn/soybean meal diets without DDGS (Almeida and Stein, 2012). This produces a greater volume of manure, which may increase the need for manure storage capacity or more frequent manure removal from swine production facilities.
Nitrogen and phosphorus excretion. It is well documented that using crystal-line amino acids and phytase in swine diets improves nutrient utilization efficiency and reduces diet cost, nitrogen and phosphorus excretion in manure and emissions of gases such as ammonia.
Kebreab et al. (2016) compared the impact of adding crystalline amino ac ids and phytase to swine diets in Europe, North America and South America. Their results showed that using these supplements in pig diets reduced GHG emissions by 56% in Europe, 17% in North America and 33% in South America versus feeding diets without supplemental synthetic amino acids and phytase. These are substantial reductions, and it is interesting to note that the North American swine diets used in this comparison contained 14.6% DDGS, but DDGS was not included in European and South American diets. As a result, the use of DDGS in swine diets can be part of the solution for minimizing the negative environmental impacts of pork production.
McDonnell et al. (2011) evaluated the effects of adding 0%, 10%, 20% or 30% corn DDGS to replace wheat in wheat- and barley-based diets — formulated on a net energy, ileal digestible amino acid and digestible phosphorus basis — on the nitrogen and phosphorus balance of growing/finishing pigs. As expected, nitrogen intake as well as urinary and total nitrogen excretion increased linearly with increasing DDGS levels in the diets (Table 1).
This was due to feeding excess nitrogen from DDGS relative to pig requirements, resulting in increased deamination of excess amino acids and increased urinary nitrogen excretion. Nitrogen retention was not affected by feeding the 10% and 20% DDGS diets, but feeding the 30% DDGS diet decreased nitrogen retention relative to nitrogen intake.
The increased nitrogen excretion commonly observed by feeding DDGS diets to swine can be minimized by using synthetic amino acids to reduce the amount of excess protein (nitrogen) in the diet.
In contrast, phosphorus intake linearly increased with increasing dietary DDGS levels, but there was no effect on phosphorus excretion or retention. These results indicate that feeding diets containing up to 30% DDGS increases nitrogen excretion but has no effect on phosphorus excretion in growing/finishing pigs when diets are formulated on a digestible amino acid and phosphorus basis.
Baker et al. (2013) compared the phosphorus balance and digestibility between dicalcium phosphate and DDGS in growing pigs and showed that although the standardized total tract digestibility (STTD) of phosphorus in DDGS was less than dicalcium phosphate, it was quite high (93% and 63%, respectively) and did result in greater fecal phosphorus excretion than dicalcium phosphate (Table 2).
However, because of the relatively high phosphorus digestibility in DDGS, diet inclusion rates may need to be reduced to minimize excess phosphorus excretion in manure. Furthermore, dicalcium phosphate is a much more expensive source of phosphorus in animal feeds, and global supplies of inorganic phosphate reserves are rapidly declining, which makes DDGS an excellent and more sustainable alternative phosphorus source in swine diets.
The addition of microbial phytase to swine diets has become a common practice to improve phosphorus digestibility, reduce phosphorus excretion in manure and lower diet costs by reducing the amount of inorganic phosphate required in the diet. Almeida and Stein (2012) added increasing levels of microbial phytase (0, 500, 1,000 or 1,599 phytase units [FTUs]) to corn or 50% DDGS diets and showed a linear improvement in STTD of phosphorus in corn (40.9%, 67.5%, 64.5% and 74.9%, respectively), and phosphorus digestibility tended to increase in DDGS diets (76.9%, 82.9%, 82.5% and 83.0%, respectively).
However, the magnitude of improvement in phosphorus digestibility by adding phytase to DDGS diets was much less than observed for corn and may not justify the additional cost of adding high amounts of phytase to swine DDGS diets.
Rojas et al. (2013) compared the phosphorus balance and digestibility of feeding growing pigs corn, DDGS and corn gluten meal with or without 600 FTUs/ kg of diet. Total phosphorus excretion was greatest for pigs fed the corn diet without phytase supplementation but was reduced by 50% when phytase was added (Table 3). However, feeding DDGS without phytase resulted in 40% less phosphorus excretion than feeding corn without phytase, and feeding corn gluten meal without phytase resulted in a 60% reduction in phosphorus excretion compared to feeding corn.
Adding phytase to the corn diet had the greatest magnitude of improvement on reducing phosphorus excretion, with no benefit in the DDGS diets and some improvement when phytase was added to the corn gluten meal diet. As a result, adding phytase to corn and corn gluten meal diets improves the STTD of phosphorus in corn and corn gluten meal but not DDGS.
This lack of response to adding phytase to DDGS diets is a result of the already high phosphorus digestibility that occurs from the degradation of phytate during the fermentation process in dry-grind ethanol plants. Therefore, formulating DDGS diets on a digestible phosphorus basis for swine can dramatically reduce phosphorus excretion in manure compared with feeding corn-based diets.
Gas, odor emissions
Feeding high-fiber diets to pigs has been shown to increase the production of methane (Jarret et al., 2011), which is a major GHG of concern. Some sources of DDGS contain significant concentrations of sulfur, which may increase the sulfur content of manure and lead to an increase in hydrogen sulfide, other reduced-sulfur compounds and odor from swine manure (Blanes-Vidal et al., 2009; Feilberg et al., 2010; Trabue et al., 2011). Furthermore, the relatively high content of protein relative to lysine in DDGS results in increased protein and nitrogen content in swine diets, which can lead to increased nitrogen excretion and potentially greater ammonia emissions in swine manure. Ammonia and hydrogen sulfide are two of the major gases produced from swine manure during storage.Several studies have been conducted to determine how feeding DDGS diets to swine affects gas and odor emissions from manure. Powers et al. (2009) measured air emissions of ammonia, hydrogen sulfide, methane and non-methane hydrocarbons when feeding growing/ finishing pigs diets containing 0% or 20% DDGS, with either supplemental inorganic or organic trace minerals. Although the organic trace mineral sources helped minimize the increased hydrogen sulfide emissions resulting from feeding the 20% DDGS diet, ammonia, methane and non-methane hydrocarbon emissions increased when feeding the DDGS diet. This is the only study that has shown an increase in ammonia and hydrogen sulfide emissions from feeding DDGS diets to pigs.
Spiehs et al. (2012) observed no differences when feeding a 20% DDGS diet compared with a corn/soybean meal diet to growing pigs over a 10-week period on total reduced sulfur, ammonia or odor concentrations.
Trabue et al. (2016) fed growing pigs diets containing 35% DDGS over a 42-day period and observed a reduction in manure pH and an increase in manure surface crust coverage, dry matter content and concentrations of carbon, nitrogen and sulfur in manure compared with pigs fed a corn/soybean meal diet (Table 4).
Warmer temperatures are often observed for manure with greater surface crusting or foam (van Weelden et al., 2015), which is associated with animals fed high-fiber diets (Misselbrook et al., 2005; Lynch et al., 2007; Wood et al., 2012) and lower pH (Kerr et al., 2006). As a result, the increased crusting of manure (Wood et al., 2012), higher temperature (Blunden and Aneja, 2008; Blunden et al., 2008; Rumsey and Aneja, 2014) and reduced pH associated with feeding DDGS diets can reduce gas emissions.
In fact, ammonia and hydrogen sulfide emissions from manure produced by pigs fed DDGS was less than from those fed a corn/soybean meal diet, but volatile fatty acid (VFA) and phenolic compound concentrations were greater in manure from pigs fed the DDGS diet (Table 4). It is likely that the increased crusting of manure from pigs fed the DDGS diet reduced hydrogen sulfide emissions by acting as a barrier for emission to the air.
Trabue et al. (2016) also measured emissions of various odor compounds from manure in the same study (Table 5). These data were normalized for pig weight (animal unit) and nutrients consumed. Pigs fed the corn/soybean meal diet had greater emissions of ammonia (53% of nitrogen consumed) and hydrogen sulfide (9% of sulfur consumed) than pigs fed the 35% DDGS diet (30% of nitrogen consumed and 2% of sulfur consumed).
These results are consistent with those from another study where ammonia emissions were reduced from feeding DDGS diets to swine (Li et al., 2011), which is likely due to the reduced pH of manure (Roberts et al., 2007) and increased microbial activity because more carbon is present in manure (Kerr et al, 2006; Ziemer et al., 2009).
However, manure from pigs fed the 35% DDGS diet had greater emissions of VFA and phenolic compounds, but there were no differences in indole emissions compared with manure from pigs fed the corn/soybean meal diet (Table 5). These differences were relatively small compared with ammonia and hydrogen sulfide emissions because total volatile organic compound emissions represented less than 1% of the total carbon consumed from feeding both diets.
Furthermore, human panelists detected no differences in the odor of com- pounds emitted from manure from pigs fed the two diets, but chemical analyses of individual odorous compounds showed greater hydrogen sulfide and ammonia and fewer total VFAs and phenols in manure emissions from pigs fed the corn/soybean meal diet than those fed the DDGS diet. The majority (60%) of odorous compounds in swine manure were derived from ammonia and hydrogen sulfide.
These data indicate that controlling nitrogen and sulfur excretion when feeding DDGS diets does not change ammonia and hydrogen sulfide emissions because the sulfur content in the DDGS diet was almost twice as high as in the corn/soybean meal diet (Trabue and Kerr, 2014), but manure hydrogen sulfide emissions from pigs fed the DDGS diet were about 30% less than those fed the corn/soybean meal diet.
Carbon dioxide, methane and nitrous oxide are major GHGs of concern in animal production systems. From the same study (Trabue et al., 2016), emissions of carbon, nitrogen and sulfur gases were also determined (Trabue and Kerr, 2014). Results showed that carbon dioxide, methane and nitrous oxide emissions, expressed on an animal unit and amount of element consumed basis, did not differ between the two diets (Table 6). However, as previously described, ammonia and hydrogen sulfide emissions were reduced by feeding the DDGS diet.
These results suggest that pigs fed DDGS diets have no greater GHG emissions from stored manure than those fed corn/soybean meal diets.
Biogas production
Van Weelden et al. (2016) showed that manure from pigs fed coarsely ground diets containing corn and soybean meal had the lowest methane production rate, while pigs fed diets containing corn/soybean meal/soybean hulls had the greatest methane production, and manure from pigs fed a 35% DDGS diet had an intermediate production rate. However, the biochemical methane production potential was greatest for the 35% DDGS diet.These results suggest that for swine farms installing biogas production systems to capture energy from manure, feeding DDGS diets would provide manure with significant amounts of carbon to generate greater amounts of methane than feeding corn/soybean meal diets.
Life-cycle assessment
There is increasing interest in conducting life-cycle assessments (LCAs) of the environmental impacts of using various feed ingredients in the swine industry. Lammers et al. (2010) conducted a partial LCA that included only the production and processing of feed ingredients used in Iowa swine diet formulations (including DDGS) and focused on non-solar energy use and global warming potential. Unfortunately, economic analyses of diets were not considered in this study, which provided misleading results.A study by Thoma et al. (2011) showed about a 6% increase in the overall carbon footprint of pork production (production to consumption) when DDGS was included in swine diets. This increase was attributed to the additional energy consumed in processing corn during the ethanol and co-product production process compared with corn grain and soybean meal.
Mackenzie et al. (2016) use a more comprehensive LCA approach to determine the environmental impacts of using co-products from human food and biofuel supply chains in pig diets in Canadian pork production systems. As shown in Table 7, on a per kilogram of feed basis, feeding corn DDGS at maximum diet inclusion rates increased non-renewable resource use by 71%, non-renewable energy use by 68% and global warming potential by 30% compared with feeding the control corn/soybean meal diets.
However, including corn DDGS in the diets reduced acidification potential by 20% and eutrophication potential by 22% versus the corn/soybean meal and all other co-product diets. When environmental impacts were expressed on a kilogram of carcass weight basis, the impacts were less dramatic but went in the same direction as when expressed on a per kilogram of feed basis.
Due to the increasing interest in and importance of reducing the carbon footprint and resource use in pork production, more of these types of comparative studies will be conducted in the future.
Conclusions
Including DDGS in swine diets can contribute to improved environmental sustainability when using net energy and digestible nutrients to formulate precision diets based on accurate net energy and nutrient digestibility estimates, which is essential to minimize nitrogen and phosphorus excretion in manure.Although DDGS is relatively high in protein and low in lysine and other amino acids relative to the pig’s requirements, the widespread availability and cost effectiveness of synthetic amino acids allows nutritionists to reduce dietary crude protein levels while meeting all of the essential amino acid requirements and reducing nitrogen excretion in manure.
One of the unique advantages of corn DDGS over other grains and grain-based ingredients is its relatively high total and digestible phosphorus content. Formulating swine and poultry diets on a digestible phosphorus basis and using phytase can significantly reduce manure phosphorus excretion. Furthermore, feeding DDGS diets to pigs does not appear to affect methane emissions but can substantially reduce ammonia and hydrogen sulfide emissions from swine manure.
Initial studies comparing DDGS with other co-product or byproduct ingredients indicate that feeding DDGS to pigs may reduce acidification and eutrophication potential by as much as 22% compared with corn/soybean meal and all other co-product diets.
References
The full list of references may be obtained by emailing tim.lundeen@ farmprogress.com.
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