Dietary L-threonine responses in laying hens

Genetic improvements in laying hens have increased egg productivity without increasing feed intake. Greater hen productivity may warrant increased ami no acid needs. However, amino acid needs of commercial layers, beyond methi onine and lysine, are poorly understood. This study ws conducted to evaluated threonine responses on egg production traits in ISA-Babcock hens after peak production. Treatments consisted of f ive levels of digestible threonine (0.43, 0.47, 0.49, 0.52, and 0.57% of di et) administered at 62-72 or 70-80 wk of age. The lowest level of digestibl e threonine (0.43% of diet) represents 100% of the 1994 NRC recommendations and a threonine:lysine ratio of 0.62. Egg production, egg weight, feed int ake, and feed conversion were measured during both time periods. Egg production (P<.011), egg weight (P<.012), and feed conversion (P<.004) improved as threonine was increased above the 1994 NRC suggested threonine recommendation. Increasing dietary threonine increased threonine intake (P< .001). A threonine:lysine ratio of 0.68 appears adequate for normal egg pro duction traits of post-peak hens.