Reduced crude protein in pig diets cut nitrogen emissions

Reducing dietary crude protein (CP) levels in finisher pig diets by 1 percent results in an 8 to 10 percent reduction in nitrogen excretion; however, it’s not the protein itself, but the amount, proportion and digestibility and availability of amino acids, which influence performance.

Concerns about sustainable soy and a lack of protein in the future has moved the agricultural agenda in recent years. Reducing dietary crude protein levels without balancing the nutritional requirements of the pig can have a detrimental impact on performance. A solution with the ability to reduce the quantity of soy required in pig finisher diets by 80 kilograms/ton (kg/t) of feed — while improving performance and costs — has been tested with promising results.

In addition, the use of sustainable protein sources also offers environmental benefits to the consumer in terms of odor reduction.

Protein supply

Pigs must be supplied with adequate levels of protein to ensure growth and lean deposition. However, if amino acid levels are wrong or amino acids are supplied in a form that pigs cannot use effectively, performance is affected. Work at the Agri-Food and Biosciences Institute (AFBI) at Hillsborough (Northern Ireland) showed a drop of 2.5 percent in growth rate and a deterioration of 3.5 percent in the feed conversion ratio (FCR) when utilizable amino acids were reduced in finishing diets.

Hence the only option has been to keep crude protein levels relatively high — 16 to 17 percent crude protein (CP) in finisher diets. The problem is that efficiency of nitrogen use in pigs is less than 40 percent. The 60 percent of nitrogen lost has used energy in the process of being consumed, digested, broken down and excreted. Therefore, it actually costs more to oversupply protein.

Soy use

Soy is a very important nutritional component of many livestock diets, particularly for pigs and poultry. However, depending on the origin of soy, it can have a high environmental impact:

  • South America: Greenhouse gases (GHG) and land use change is associated with deforestation and plowing up of high nature value or virgin land, especially in Brazil. The majority of soy used in U.K. and EU diets is of South American origin.
  • North America: Soil loss is a huge issue in the Corn Belt, particularly in states like Iowa. The U.S. government allows soil loss tolerance levels of around 5 tons per acre per year but, in reality, soil loss can rise to 40 tons/acre during extreme weather events.

The European Commission is in the process of developing an EU protein plan in an attempt to increase the self sufficiency of Europe by promoting the cultivation of protein crops. However, there is recognition that protein-rich feeds such as soy are needed in livestock diets and it is not possible to simply substitute with lower-protein raw materials, as they may not be able to adequately meet the needs of the animal.

Sustainable protein sources

A protein optimizer feed ingredient has been developed to deliver amino acids in a highly available form. Approximately 80 kg of soy can be replaced in a pig finisher diet with 10 kg of the product. The subsequent formulation results in a 25 percent reduction in nitrogen excretion and 16 percent reduction in GHGs. 

Dr. Violet Beattie, research and technical services manager with Devenish Nutrition, described the science behind this new concept.

“The product consists of amino acids reversibly bound to sugars, allowing them to be released during digestion and efficiently utilized by the pig,” Beattie says. “By adding the protein optimizer to the diet, the protein in the diet is optimized and overall CP level can be reduced.”

This has the effect of sparing energy in the diet and hence promoting growth.

Finisher Pig Performance Comparison

Performance comparison of finishing pigs fed a 14 percent CP plus protein optimizer or a 17 percent CP control diet. | Devenish Nutrition

Commercial experience

In a series of trials, CP was reduced from 17 to 14 percent, with the inclusion of 10 kg/t of protein optimizer. Eight evaluations were carried out at AFBI Hillsborough, Harper Adams and on commercial units across the U.K. and Ireland. The trials covered a range of starting weights from 30 to 60 kg and on-farm growth rates from 730 to 1,050 grams/day (g/d) — representative of most finishing units.

“A 14 percent CP diet including the protein optimizer was found to outperform a 17 percent CP diet in the trials,” Beattie says. “Now over a million pigs have been finished using this concept.”

Nitrogen, ammonia emissions

Ammonia is a hot topic at the moment, particularly in U.K. and Ireland, but also relevant to other EU countries. Most of Northern Ireland (NI) is said to be exceeding nitrogen deposition critical loads. This is the concentration of nitrogen at which significant ecological damage occurs, which can be attributed to ammonia emissions. 

“Ninety-one percent of ammonia emissions in [Northern Ireland] come from agriculture, so the sector is firmly in the spotlight at the moment,” says Gill Gallagher, Devenish Nutrition’s sustainable agriculture manager. “As a result, the growth of the industry is being constrained as planning permission is becoming harder to get due to ammonia emissions.”

As such, a working group of experts produced a report titled, “Making Ammonia Visible,” which explicitly cites crude protein reductions in livestock diets as a mitigation measure. 

Studies have shown that reducing CP by 1 percent can result in an 8 to 10 percent reduction in ammonia emissions.

Greenhouse gases

The link between the greenhouse gases (GHG) emitted by livestock and climate change are well documented. However, more efficient production can actually reduce the carbon intensity of production via diet and management. 

SAC Consulting, which has a carbon foot printing tool called Agricultural Resource Efficiency Calculator (AgRE Calc), has independently validated the protein optimizer concept.

“The results from the tool show that pigs fed a diet containing the protein optimizer can have up to a 16 percent lower carbon footprint,” Beattie says. 

This is primarily due to performance benefits as well as the reduced use of soy.

The 10 kg of the protein optimizer can replace 80 kg of soy in finisher diets, reducing 25 percent of nitrogen excretion and 16 percent of GHGs with this formulation. | Devenish Nutrition

Consumer benefits

Increasing the “green” credentials of pork could be good for sales as well as the environment — particularly as consumers become more discerning about their food choices. Gallagher says the case study shows the overall environmental benefits of using the protein optimizer to reduce CP levels in finishing pigs.

“Water is predicted to be the greatest limiting factor to agricultural production and conserving supplies is a major global concern for everyone,” he says. “Using a protein optimizer has been shown to reduce the water intake of pigs during the finishing period.”

Slurry is an extremely valuable and important nutrient resource/fertilizer. However, problems can arise where too much slurry is produced relative to the amount of land available for spreading it. 

“The EU Nitrates Directive limits the amount of nitrogen which can be applied to the land,” Gallagher says. “Another benefit of this concept is that the quantity of slurry produced during the finishing period is reduced.”

Trials examining the effect of feeding the protein optimizer on ammonia excretion and odor from finishing pigs are ongoing — the later being an issue for those living close to pig farms.

“Preliminary results show reductions in both ammonia and odor,” says Gallagher.

A sustainable future

As well as environmental sustainability, this concept also could help the economic sustainability of pig production.

Diets utilizing the protein optimizer were cheaper and performance at least equal. This means that the cost per kilogram of liveweight gained is reduced. A financial exercise was carried out based on the eight trials detailed plus a further five commercial evaluations.

“Assuming cost of raw materials as they are today, by reducing crude protein levels and using a protein optimizer, diet costs were reduced by GBP1.55 (US$2.02) per pig over the finishing period and cost per kilogram gained by GBP0.03 on a carcass basis,” says Beattie. “Even if you assume the diets cost the same, producers would still save GBP0.55 pence per pig or GBP0.02 per kilogram of gain.”

This is a sustainable strategy in a world where protein is going to be limited in the future.

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