Evaluation of the threonine requirement and the bioavailability of threonine in feedstuffs in pregnant sows

Current recommendations for amino acid intake during pregnancy are for a constant amino acid intake throughout. However, the demand for amino acids changes from maternal tissue growth in early gestation to fetal, conceptus and mammary tissue development in late gestation. The availability of amino acids from feed ingredients are based on growing pig data, although recent evidence suggests that mature animals have a greater capacity to digest and absorb amino acids. Therefore, this thesis investigated the threonine requirement of sows in gestation and the availability of threonine (Thr) in common feed ingredients fed directly to sows using the indicator amino acid oxidation technique.;In conclusion, current sow amino acid requirement recommendations do not appropriately reflect actual amino acid demand during pregnancy. The deficiency in dietary amino acids during late gestation may result in maternal lean tissue catabolism to support fetal growth. The greater availability of amino acids from feed ingredients in sows may reduce the degree of amino acid deficiency in late gestation under current feeding programs. Application of phase feeding sows during pregnancy will more closely meet the demand for amino acids and may improve sow reproductive longevity.;The Thr requirement in early gestation was determined to be 5.0 to 6.0 g/d, at least 40% below current recommended Thr requirements, whereas the requirement for Thr in late gestation was determined to be 12.3 to 13.6 g/d, close to 30% above current recommendations. These results suggest that current sow feeding recommendations (i.e. constant level of AA throughout gestation) result in over- and under-feeding AA in early and late gestation, respectively. The metabolic availability of Thr in corn and barley fed to growing pigs was 82.2 and 115.3%, respectively, whereas when fed to pregnant sows, the metabolic availability of Thr in corn and barley was 88.0 and 89.3%, respectively. The > 100% availability of Thr from barley was likely due to the effect of barley on the demand for Thr for production of mucin and mucous proteins. The results indicate that the availability of amino acids from feed ingredients is greater when fed to sows than when fed to growing pigs.