How feeding programs affect environmental impacts of pork production
By Zhaohui Yang, Pedro Urriola, Lee Johnston and Gerald Shurson
Nitrogen (protein) and phosphorus are the second and third most expensive components of swine diets, respectively, after energy. However, the cost of these essential nutrients is much greater because only 10 to 44% of dietary N and 34% of P in swine diets is converted into boneless edible lean pork1.
Similar inefficiencies also apply toward producing meat, milk and eggs from other food producing animals, and are the main reason why the global livestock and poultry industry contributes about one-third of total human-induced N emissions2.
As a result, the earth’s planetary boundaries for N3 and P4 waste and recovery have been exceeded, which requires implementing practices that improve N2 and P5 utilization efficiency and reduce the carbon footprint of animal production systems1.
About 68% of N emissions2 and 47% of greenhouse gas (GHG) emissions6, which include carbon dioxide, methane and nitrous oxide from livestock farms are associated with feed production. Traditional swine diet formulation approaches have focused on minimizing cost while meeting energy and nutrient requirements to achieve acceptable growth performance and carcass characteristics but often with little regard toward minimizing environmental impacts.
Soybean meal continues to be an excellent dietary protein source for swine because of its complementary amino acid profile with corn and high digestible amino acid concentrations, but there are several formulation practices that can partially replace soybean meal in swine diets.
Corn distillers dried grains with solubles (DDGS) is produced in large quantities and often less expensive than corn and soybean meal, and is commonly added at levels up to 30% in growing-finishing swine diets. However, high inclusion of DDGS in swine diets can result in suboptimal growth performance and carcass composition if diet formulation adjustments are not made to overcome digestible amino acid imbalances.
Also, the addition of relatively high amounts of crystalline amino acids to reduced crude protein in swine diets is becoming a popular strategy to reduce the amount of soybean meal used and diet cost, but this strategy can also result in suboptimal growth performance and carcass composition.
Types and sources of feed ingredients, diet formulation approaches and feeding practices not only affect lean gain efficiency, but also the environmental impacts of pork production. Precision diet formulation and feeding programs have been shown to reduce cost of production by more than 8%, protein and phosphorus intake by 25% and excretion by 40%, and GHG emissions by 6% through improved nutrient utilization efficiency7 in commercial pork production systems.
Therefore, we conducted a series of studies (funded by the United Soybean Board) to determine the N (and P) utilization efficiency and other environmental impacts of grower-finisher feeding programs containing variable amounts of soybean meal as the primary protein source, without and with 30% DDGS, crystalline amino acids and phytase using precision diet formulation approaches to achieve optimal growth performance and carcass composition.
Precision diet formulation was based on using dynamically determined net energy, digestible amino acid and phosphorus nutrient loading values for the sources of corn, soybean meal and DDGS being fed.
Diets within each of the following 4-phase feeding programs consisted of:
The first study was conducted to determine effects of feeding program on growth performance and carcass characteristics. A total of 288 pigs (initial BW = 80 lb.) were fed for 12-wk at the University of Minnesota West Central Research and Outreach Center (Morris, Minnesota), scanned to obtain backfat and loin muscle area measurements before shipping, and were slaughtered at Hormel Foods (Austin, Minnesota) to obtain hot carcass weights of individual pigs.
No differences were observed in average daily gain and feed intake, but pigs fed CSBM had greater (P < 0.05) final BW than those fed LP and DDGS, and greater (P < 0.05) gain efficiency than pigs fed LP. However, supplementing crystalline isoleucine, valine and tryptophan in diets containing high levels of DDGS improved final body weight of pigs compared to feeding the DDGS diets without these dietary amino acid adjustments.
No differences were observed for hot carcass weight, carcass yield or carcass fat-free lean percentage among pigs fed any of the four feeding programs. Therefore, these results indicate that CSBM and DDGS+IVT feeding programs provided the greatest gain efficiency but provided no advantages for carcass lean percentage compared with the other feeding programs.
Figure 1. Growth performance of growing-finishing pigs fed the 4 feeding programs.
Figure 2. Carcass characteristics (hot carcass weight, carcass yield, carcass fat-free lean) of growing-finishing pigs fed the 4 feeding programs.
The second study was conducted to determine the effects of feeding the phase 2 grower diets used in each of the four feeding programs evaluated in the first study, on nitrogen and phosphorous balance. A total of 32 barrows (initial BW = 130 lb.) were housed in metabolism crates at the University of Minnesota Southern Research and Outreach Center (Waseca, Minnesota) for a 12-day metabolism study.
Pigs fed the CSBM diet had a greater (P< 0.05) amount of N retained than pigs fed the other diets, but also had a greater (P < 0.05) amount of urinary N excretion and blood urea N than pigs fed the LP and DDGS+IVT diets. Pigs fed the LP diet tended (P < 0.10) to have the highest N utilization efficiency but the lowest (P < 0.05) percentage P retained as a percentage of P intake among diets.
Figure 3. Nitrogen balance of growing-finishing pigs fed the grower 2 diets in each of the 4 feeding programs.
Using the growth performance and carcass composition data from the previous experiments, we determined the Life Cycle Assessment (LCA) of the environmental impacts of producing 1000 kg (2,205 lbs) of pork carcass weight from each feeding program using the Opteinics software (BASF, Lampertheim, Germany).
Life cycle assessment is a systematic analysis to quantify the environmental impacts of inputs and outputs of products during the entire life cycle. Our results showed that the CSBM feeding program had the least impact on climate change (GHG emissions), marine eutrophication, freshwater eutrophication and fossil resource use, while the LP feeding program had the least impact on acidification, terrestrial eutrophication and water use among the four feeding programs evaluated. The DDGS and DDGS+IVT feeding programs had the lowest impact on land use.
Figure 4. Environmental impacts of pork production systems using the four growing-finishing feeding programs (CSBM as a reference diet).
These results indicate that while all these feeding programs were superior to the other feeding programs in one or more of environmental impact measures, none of them were superior in all criteria. However, the CSBM feeding program provided optimal growth performance and carcass composition of growing-finishing pigs while simultaneously reducing impacts on climate change, eutrophication potential and fossil resource use compared with the other feeding programs evaluated.
Results from this study demonstrate how the use of LCA data for assessing various environmental impacts of feed ingredients, diets and feeding programs can provide important information that enables pork producers to choose feeding programs that meet specific sustainability goals.
Moving forward, sustainable swine feeding programs must be based on using multi-objective feed formulation that puts constraints on high priority LCA environmental impact measures that involve N and P utilization efficiency, GHG emissions, water consumption and land use in additional to meeting nutritional requirements to optimize pig performance and carcass composition at a reasonable cost.
This will require integration with real-time determination of nutrient loading values of actual sources of feed ingredients used in feed formulation and precision feeding practices to “get the right feed to the right pigs at the right time.”
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Yang is a research assistant and Ph.D. candidate, Urriola is a research associate professor, and Johnston and Shurson are professors, all with the Department of Animal Science, University of Minnesota.
