Chickens' growth performance and pancreas development exposed to soy cake varying in trypsin inhibitor activity, heat-degraded lysine concentration, and protein solubility in potassium hydroxide

This study focused on the effect of varying trypsin inhibitor activity (TIA), heat-degraded lysine concentration and protein solubility in potassium hydroxide on broiler performance and pancreas weight. Two soybean breeds were subject to varying thermal, hydrothermal, pressure, and kilning processing. This resulted in a total of 34 soy cake variants, widely varying in TIA (0.25 to 23.6 mg/g), heat-degraded lysine (1.40 to 8.60 g/kg), and potassium hydroxide (65.5 to 97.6%), respectively. These soy cake variants as well as a commercial soybean meal extract were included into a common grower and finisher diet for broiler chicks at fixed amounts (grower: 35%; finisher: 25%) and tested in a 35 d fattening experiment with 1680 broiler chicks (grower phase: day 11 to 24; finisher phase day 25 to 35). TIA was the dominant factor affecting zootechnical performance and pancreas weight at slaughter (day 35), depressing liveweight at day 24 (P < 0.006), and day 35 (0.026), weight gain (grower: P < 0.006) and feed: gain ratio during grower phase (P < 0.005) and increasing pancreas weight (P < 0.010) at the time of slaughter. Negative effects of TIA were also visible in soy cake variants below recommended thresholds. This highlights the necessity of complete elimination of TIA in broiler diets as far as technically possible.