Because Protein Digestibility is Heritable, it Represents a Promising New Trait for Future Inclusion in Breeding Programs to Improve Resource Utilization, Strengthen Production Economics, and Reduce Swine-Related Greenhouse Gas Emissions.

By Kristine Hov Martinsen. PhD

Pig breeding has traditionally achieved great success in improving production and feed efficiency through selection for improved feed conversion ratio, reduced backfat, increased lean meat percentage, and high growth.

Over the past six decades, continuous genetic improvements have dramatically enhanced overall feed efficiency. While these advances have significantly improved how efficiently pigs convert feed into meat, they do not fully capture how well nutrients are absorbed in the intestines.

The next step in improving feed efficiency is coming from a more efficient use of nutrients, low maintenance requirements, and optimized gut health.

PROTEIN DIGESTIBILITY AS A NEW SELECTION TRAIT

Research conducted by Topigs Norsvin in collaboration with the Norwegian University of Life Sciences has identified protein digestibility as a new and promising trait. This trait captures the pig’s ability to absorb and better utilize the proteins in feed, enabling a more precise approach to improving nutrient efficiency.

Using Near-Infrared Spectroscopy, the nutrient content of feces can be measured in a cost-effective and scalable way.

By combining feed composition with fecal nutrient data, it is possible to estimate how efficiently nutrients are absorbed in the intestine. Studies have shown that protein digestibility is heritable, with genetics explaining approximately 20% of the variation in this trait.

In addition, favorable correlations have been identified with traits currently included in the Topigs Norsvin breeding goal for feed efficiency. This enables selection for improved protein digestibility.

IMPACT OF PROTEIN EFFICIENCY

Efficient protein utilization has a significant impact across the production system:

• Reduced feed consumption lowers production costs.
• Improved resource utilization reduces the overall environmental footprint.
• Lower nitrogen excretion reduces emissions from manure.
• The development of more robust pigs with stable and consistent growth performance.

In pork production, feed accounts for approximately 75% of production costs and around 80% of climate impact. As a result, even small improvements in protein utilization can deliver substantial benefits, such as for production efficiency, environmental sustainability, and animal performance.

FROM PROTEIN TO EMISSIONS

Protein in feed is a primary source of nitrogen. It consists of amino acids, which are broken down in the intestine and absorbed for use in biological processes such as growth and protein deposition.

Not all proteins are utilized efficiently. Undigested amino acids are excreted in feces, while excess absorbed nitrogen is excreted via urine (primarily as urea). As a result, a significant proportion of nitrogen ends up in manure, which is used as natural fertilizer in crop production.

During manure storage and application, nitrogen compounds are converted through biological processes. Ammonium (NH₄) can be transformed into nitrate (NO₃), releasing nitrous oxide (N₂O) as a byproduct.

Nitrous oxide is a highly potent greenhouse gas, approximately 300 times more impactful than CO² per molecule. Emissions from pigs account for around 20% of total emissions in pork production and include both methane and nitrous oxide. Methane originates from digestion and represents a smaller share, while nitrous oxide is the primary concern, arising from undigested and excess protein excreted in manure.

Better protein utilization in pigs leads to reduced nitrogen excretion in manure, lowering nitrous oxide emissions. At the same time, it reduces the need for imported protein sources such as soy and rapeseed, lowers feed costs, and increases the opportunity to use locally sourced feed ingredients.

GENETIC IMPACT ON PROTEIN UTILIZATION

Through the Topigs Norsvin breeding program, improving protein digestibility by 2.2% (one genetic standard deviation) is predicted to increase the proportion of protein absorbed in the intestine, resulting in approximately 1.3 kg (2.87 lbs) less protein required per slaughter pig.

This improvement is also expected to reduce total greenhouse gas emissions by around 0.8%, primarily through reduced nitrous oxide emissions from housing, manure storage, and manure application.

IMPLICATIONS FOR FEED FORMULATION AND COST

When protein digestibility increases by 2.2%, a larger proportion of dietary protein is absorbed and utilized by the animal. Assuming that nutrient requirements for maintenance, growth, and protein deposition are met, the protein content in feed can be reduced by approximately five grams per kilogram (~0.08 ounces per pound).

This improved efficiency enables greater use of locally sourced feed ingredients, such as barley, while reducing reliance on imported protein sources like soy and canola. Protein-rich raw materials are among the most expensive components of feed and they vary by region, this creates clear opportunities to lower feed costs.

ABOUT THE RESEARCH

Topigs Norsvin participated in the research project, which was owned by NMBU and financed through the Research Council of Norway’s funding for the agriculture and food industry. Nofima contributed with method calibration. Participants from Topigs Norsvin included researchers Kristine Hov Martinsen and Eli Gjerlaug Enger.

Kristine Hov Martinsen, PhD
Topigs Norsvin

Kristine Hov Martinsen is a researcher in the Health & Behavior Platform and Nutrition Platform at Topigs Norsvin. Holding a PhD in Quantitative Genetics, she focuses on animal behavior and feed efficiency, working at the intersection of genetics and phenotyping. Her research contributes to a deeper understanding of how genetic factors shape behavioral traits and resource utilization in pigs.