Threonine incorporation in tissues of growing broiler chickens using L-[¹⁵ N] threonine

Most amino acid requirement trials appear for whole-body responses, but there is little information concerning amino acid incorporation in individual tissues, which may vary according to the age. L-[¹⁵ N] threonine was used to evaluate its incorporation rate and distribution among broiler tissues in different ages. Seventy-two male broiler chickens were distributed into three different phases: starter (4 to 9 days old), grower (18 to 23 days old) and finisher phase (32 to 37 days old). L-[¹⁵ N] threonine was added on balanced diets, and birds were fed for five days in each phase. Enriched samples of breast muscle, feathers, liver, jejunum and plasma were collected at 0, 6, 12, 24, 48, 72, 96 and 120 hr after fed birds with the tracer in each phase. In the tissues were analysed dry matter, nitrogen and stable nitrogen. The ¹⁵ N isotope abundance according to the time was fitted into exponential or linear equations using a same intercept. The ratio of the steepness or slope coefficients was determined to compare the L-[¹⁵ N] threonine incorporation according to the age. In addition, L-[¹⁵ N] threonine mass balances were performed to assess the L-[¹⁵ N] threonine distribution among the evaluated tissues. Except for feathers, the L-[¹⁵ N] threonine incorporation rate decreased with ageing. Taking into account the L-[¹⁵ N] threonine distribution in the tissues, only in the jejunum was not observed an increase as the broiler grew. The L-[¹⁵ N] incorporation varied in each tissue and according to the age of the broiler chickens. These outcomes could be useful to comprehend changes in amino acid requirements tissue-specific according to age.