What's the story on Threonine Requirement?

Marcia Shannon
State Swine Nutrition Specialist
University of Missouri
Phone: (573) 882-7859

The pig does not have a specific requirement for crude protein, but rather the components that make up protein called amino acids. The first limiting amino acid in a corn-soybean meal diet fed to swine is lysine. Nutritionists balance swine diets to meet the lysine requirement with all other amino acids supplied as ratios to lysine or as a percent of lysine know as the ideal protein ratio (Table 1).

Threonine was the last essential amino acid to be discovered and characterized. The importance of threonine in swine diets has been overlooked largely due to the lack of understanding of threonine nutrition and the high price of the synthetic form of threonine. Research has shown for a need to supplement synthetic threonine in order to improve growth performance and carcass quality. This could result due to the order of limiting amino acids in particular diets. Typically, if the first limiting amino acid is not supplemented, but the second or third limiting amino acids do satisfy the requirement then growth performance will be depressed. Likewise, when the requirement for the first limiting amino acids has been meet, adding the third limiting amino acid without satisfying the second limiting amino acid will result in no further improvement in growth performance. Therefore, it is critical to ensure that synthetic amino acids are added in the right order or sequence.

Synthetic lysine and methionine are commonly added to swine diets to meet the requirements. Threonine is often assumed to be adequate in corn-soybean meal based swine diets. Recent research has shown that the requirement for apparent digestible threonine is not more than 60% of lysine for 18 to 40 lb pigs, which is the NRC requirement.

In conclusion, many factors affect amino acid requirements including age, body weight, sex, genotype, environment (climate, microbial, social), and dietary factors. With these multiple factors, it is rather difficult and impractical to conduct experiments to determine the amino acid requirements for each individual group of pigs and situation.

Table 1. Amino Acid Ratio for Grow-Finish Pigs (50 to 250 lbs).
Amino AcidTotal basis
Methionine and Cys55