Research At Illinois Studies Importance Of Threonine:Lysine Ratio In Pig Diets

   • The ideal threonine:lysine ratio in diets fed to growing pigs has not yet been conclusively established.
   • High levels of dietary fiber may increase the requirement for threonine in the diet.
   • A threonine:lysine ratio of 0.71 was required to optimize average daily gain in pigs fed high-fiber diets, compared with a ratio 0.66 for pigs fed low fiber-diets.
   URBANA, ILL.
   To optimize performance in growing pigs, it is important to feed not only enough protein, but the right balance of amino acids. Research from the University of Illinois is helping to determine the correct ratio of threonine to lysine in pig diets, and how this ratio is affected by the fiber content of the diets.
   Hans H. Stein, professor of animal sciences at Illinois, explains that because producers are increasingly feeding lower-cost, high-fiber coproducts, it's important to understand how dietary fiber affects pigs’ nutritional needs. “There’s been some confusion about the ideal threonine to lysine ratio,” says Stein. “We think one reason may be that studies have been conducted using diets with different levels of dietary fiber."
   Stein says that increased levels of dietary fiber may result in a greater requirement for threonine because of decreased transit time of digesta, increased endogenous loss of threonine, and increased microbial activity in the hindgut.
   A team of researchers headed by Stein formulated low-fiber diets based on corn, field peas, soybean meal, and corn starch, as well as high-fiber diets in which the corn starch was replaced by soybean hulls. Both low- and high-fiber diets were then supplemented with threonine to achieve a standardized ileal digestible threonine:lysine (SID Thr:Lys) ratio of 0.45, 0.54, 0.63, 0.72, 0.81, or 0.90.
   After analyzing growth performance data for pigs fed the twelve experimental diets, Stein's team estimated that the ideal Thr:Lys ratio for optimizing the gain:feed ratio was 0.63 for both low- and high-fiber diets. However, to optimize average daily gain, pigs fed low-fiber diets required a Thr:Lys ratio of 0.66, whereas pigs fed the high-fiber diets required a ratio of 0.71.
   “This increase in the estimated requirement indicates that the presence of soybean hulls, a source of both soluble and insoluble fiber, in the diet increases the requirement for threonine in growing pigs,” says Stein.
   Funding for this research was provided by Ajinomoto Heartland (Chicago, IL), and by Evonik Nutrition & Care GmbH (Hanau-Wolfgang, Germany).
   The paper, “Effects of dietary fiber on the ideal standardized ileal digestible threonine:lysine ratio for twenty-five to fifty kilogram growing gilts,” was co-authored by John Mathai of Illinois, John Htoo of Evonik Nutrition & Care GmbH, John Thomson of Evonik Degussa Corporation in Kennesaw, Georgia, and Kevin Touchette of Ajinomoto Heartland Inc. It was published in a recent issue of the Journal of Animal Science, and can be found online at https://www.animalsciencepublications.org/publications/jas/articles/94/10/4217. ∆