Nitrogen compounds derived from excess amino acids in crude protein ingredients in swine feed end up in manure and urine, from which they contribute significantly to the carbon footprint of animal agriculture. Those excreted nitrogen compounds can be oxidized by soil and air, and some of it is released into the atmosphere as nitrous oxide.
Nitrous oxide has a greenhouse gas effect that is 298 times that of carbon dioxide. It has the next largest impact on global warming after CO2 and methane.
Amino acids are essential for proper tissue development in animals. A number of these are particularly critical, including lysine, valine, isoleucine and histidine, among others. They are called “limiting amino acids” because insufficient concentrations of them can impair growth performance. They are present in naturally occurring concentrations in crude protein sources, including corn and soybean meal. But they are not balanced for swine and other animals. When crude proteins are mixed in feed to provide sufficient lysine, for example, they will also add excessive amounts of other amino acids. Those excesses are converted to nitrogen by the animal’s metabolism and excreted in urine and manure.
Charles Maxwell, professor of swine nutrition and management for the Arkansas Agricultural Experiment Station, the research arm of the University of Arkansas System Division of Agriculture, and research associate Tsung Cheng Tsai devised experiments to evaluate whether reformulating swine feed with amino acid supplements could mitigate greenhouse gas emission from swine production systems and still meet the nutrition requirements of nursery and grow-finish diets.
The trick, Maxwell said, is to replace as much of the crude protein as possible with supplements of limiting amino acids without disrupting the total nutritional needs of the pigs.
Maxwell and Tsai designed five experiments — two nursery studies and three grow-finish studies —in an attempt to define the practical limits for the replacement of crude proteins in swine diets with feed grade amino acids without impairing growth performance or carcass composition. The experiments were carried out at the Division of Agriculture wean-to-finish swine facilities at the Savoy Research Complex in Washington County.
The goal of the experiments was to develop high inclusion of amino acids in diets that would achieve the same gain and efficiency as feeding protein-based diets. That goal was achieved with the seven top limiting amino acids. The experiments demonstrated that replacing crude proteins in hog diets with feed grade amino acids can reduce the carbon footprint of swine production. During these studies, Maxwell and Tsai were able to find successful ratios for replacing crude proteins with feed grade amino acids at multiple stages of pig growth from nursery through finishing.
The prices of commercially available amino acid supplements are relatively low, helping to reduce feed costs while maintaining animal health and production.
Hogs and pigs add nearly $51.9 million to Arkansas’ agricultural economy, according to the 2020 Arkansas Agricultural Profile (https://bit.ly/AAES-2020PocketFacts), published by the Division of Agriculture. Maxwell and Tsai’s research demonstrated that substituting commercial amino acid supplements for crude amino acid sources saved money on feed costs at all stages of pig development while reducing excreted nitrogen and maintaining animal health and production.