By Eduardo Beltranena and Mahmoud Sharara, North Carolina State University
Over three decades, the swine industry has substantially reduced phosphorus (P) excretion (30–60%). Nitrogen (N) is the current challenge in progress. Protein rich in N is the second most expensive dietary nutrient and a major contributor to ammonia (NH₃) and nitrous oxide (N₂O) emissions. Some strategies are already being implemented but need expansion.
Feeding Strategies
1. Feed lower crude protein diets.
Balancing for amino acids (AA) reduces dietary protein cutting urinary N, the primary source of barn NH₃ volatilization.
2. Include crystalline AA.
Adding crystalline AA instead of protein meals lowers dietary protein while meeting growth needs, reducing deamination losses.
3. Formulate on digestible AA.
Formulating diets on standardized ileal digestibility improves AA utilization and lowers urinary N by 10–20%.
4. Shift N from urine to feces.
Adding soluble fiber (e.g., wheat bran, DDGS) feeds hindgut microbes that convert urea into microbial protein, reducing urinary N by 10–30%.
5. Feed slower-digestible proteins.
Protein in canola meal or pulses is digested more slowly, promoting microbial use and lowering urinary N by 5–15%.
6. Synchronize protein and starch digestion.
Matching protein and starch digestion rates improves nutrient utilization enhancing N retention.
7. Add proteases, prebiotics and resistant starch.
These enhance diet digestibility by young pigs and microbial N capture, cutting urinary N by 5–15%.
8. Match AA supply to growth.
Changing diets as often as barn feed bins fill, reduces protein oversupply and improves N utilization by 3–7%.
9. Adopt precision feeding.
Forthcoming automated feeders blend high and low diets to match the growth curve of individual pigs within pen reducing N excretion.
10. Promote gut health.
Minimizing weaning stress and enteric diseases promote gut stability and reduce N losses.
Manure Strategies
1. Separate feces from urine.
Barn V-belt separators sieve feces from urine preventing barn urea breakdown and NH₃ release.
2. Solid–liquid sludge separation.
Outdoor centrifuges, presses and settling basins reduce N losses when in-barn segregation isn’t feasible.
3. Add acids to manure.
Acidifying manure pits keeps N as ammonium (NH4), reducing barn NH₃ release that affect both workers and pigs.
4. Install manure tank or lagoon covers.
Covers limit gas exchange and allow methane capture or flaring.
5. Time manure applications.
Apply manure as close to crop peak N demand to improve nutrient uptake.
6. Improve crop manure placement.
Place manure on the most ideal spot for the crop to maximize plant nutrient uptake.
7. Incorporate manure promptly.
Inject or incorporate promptly manure spread on top to minimize surface losses and runoff.
8. Weather at time of application.
Avoid hot, windy or rainy days to prevent N volatilization and runoff.
9. Calibrate application equipment.
Proper nozzle selection and calibration ensure uniform N delivery and over application.
10. Analyze soil and manure.
Soil and manure testing and in-line sensors enable variable-rate application.
Together, improved feeding, manure handling and precision applications can substantially reduce ammonia and greenhouse gas emissions, lower nutrient losses and enhance manure’s value as a fertilizer shrinking the pork industry nitrogen footprint.
