Effect of chemical composition of sunflower seed meal on its true metabolizable energy and amino acid digestibility.

The effect of chemical composition of sunflower seed meal (SFSM) on TMEn and true amino acid digestibility (TAAD) was studied. In Experiment 1, the excretion pattern of three SFSM samples force-fed (30 g) to 10 adult cockerels (Hy-Line) each was followed for 84 h to determine the time interval for complete excretion of SFSM. Type of SFSM did not affect the excretion pattern of DM and energy (P=0.438, and P=0.189, respectively). Dry matter and energy excreted every 12 h decreased linear and quadratically (P < 0.001) with collection time. No differences were found from 48 h collection time on. So, an excreta collection period of 48 h was considered adequate for determining the TMEn of SFSM. In Experiment 2, 135 adult cockerels were force-fed to determine the TMEn of 11 samples of SFSM. Type of SFSM affected TMEn (P < 0.001), which ranged from 1,558 to 2,023 kcal/kg DM for SFSM of 31 to 42% CP, respectively. The TMEn was highly correlated (P < 0.001) to hemicellulose (r=-0.90), acid detergent lignin (r=-0.84), neutral detergent fiber (r=-0.82), and CP (r=0.77). Four prediction equations are proposed, the most practical being: TMEn (kcal/kg DM)=2,816.8 - 109.5 hemicellulose (%DM), RSD=70.2. Three out of the 11 samples of SFSM were selected for determining TAAD and the effect of endogenous amino acid correction. The methodology used was that of the TMEn assay, but one more estimation of amino acid endogenous excretion was made using a N-free diet with 85% cornstarch and 15% cellulose. Endogenous amino acid excretion was greater for roosters fed the N-free diet than those deprived of feed, resulting in a higher digestibility (from 0.7 to 2.7%, P < 0.05) only for six amino acids: threonine, valine, alanine, proline, and aspartic and glutamic acids. No interaction was detected (P=0.94) between type of SFSM and method of estimation of endogenous amino acid excretion. The TAAD of SFSM increased significantly (P < 0.001) with the CP content, total TAAD being 86, 88, and 89% for SFSM of 32, 35, and 37% CP, respectively. Attention should be paid when including high fiber-low protein SFSM in poultry diets to balance its lesser digestible amino acids contribution, mainly in lysine (from 0.77 to 1.06% for SFSM of 32 and 37% CP, respectively).