Lysine and tryptophan levels in diets for gilts from 15 to 30 kg of body weight
The aim of this study was to determine the optimum levels of digestible lysine (Lys) and tryptophan (Trp) in diets for gilts from 15 to 30 kg of body weight. A previous study was carried out to determine the true ileal digestibility of amino acids in the basal diet (low Lys and Trp levels), in order to verify if some deficiencies occurred with other essential amino acids. The growth performance study was performed using a total of 64 individually housed gilts (15,03±0,19 kg), allotted in a completely randomized block design, with 16 treatments and four replicates. Treatments were arranged as a 4 x 4 factorial scheme (four levels of digestible Trp: 0.155, 0.185, 0.215, 0.245% and four levels of digestible Lys: 0.972, 1.112, 1.252 and 1.392%). Glutamic acid was used to keep nitrogen levels similar across diets. The body weight (BW) and feed intake were recorded and F:G was calculated. Ultrasonography was performed using an Aloka (SSD 500) and Sonograder (Renco®) equipments, and backfat thickness and loin depth were measured using the ImageJ software. Considering the regression analysis, a quadratic effect of digestible levels of Trp was observed on ADG (P= 0.038), in which the optimum level was obtained 0.224%. The increased levels of digestible Trp improved linearly (P= 0.005) the ADFI. An interaction between Trp and Lys was observed for F:G (P= 0.007). No interaction was observed for ADG (P= 0.247), ADFI (P= 0.233), backfat measured with Sonograder (P= 0.603), and Aloka (P= 0.462) and for loin depth measured with Sonograder (P= 0.632) and Aloka (P= 0.086). By surface response method, a quadratic effect (P= 0.034) of digestible levels of Trp and a linear effect of Lys (P= 0.005) were observed on F:G , in which the optimum level of digestible Trp was obtained at 0.216%. Trough regression equation method, the backfat thickness (measured through Aloka or Sonograder) increased linearly (P= 0.052 and 0.021, respectively) and the loin depth (measure through Aloka) showed quadratic effect (P= 0.034) for Trp levels, in which the optimum level was estimated at 0.205%. The loin depth, measured through Sonograder, increased linearly (P= 0.039) with digestible levels of Lys. In conclusion, the optimum levels of digestible Trp, to improve average daily gain and loin depth, are 0.224 and 0.205%, respectively.
Keywords: amino acids, ileal digestibility, growth performance.