The protein oxidation of soybean meal induced by heating decreases its protein digestion in vitro and impairs growth performance and digestive function in broilers

1. The soybean meal (SBM) was heated at 100°C for 1, 2, 4 and 8 h, respectively, and their resultant oxidative status was evaluated.

2. A total of 400 one-day-old Arbor Acres broilers were randomly divided into 5 treatments with 8 replicates of 10 birds each, and fed with diets containing non-heated SBM (NHSBM) or 1 of 4 heated SBMs (HSBMs, SBMs heated at 100°C for 1, 2, 4 and 8 h, respectively) for 42 d.

3. The contents of carbonyl in the SBMs were both linearly and quadratically increased, whereas the nitrogen solubility index, and in vitro digestibility of crude protein (CP) and dry matter (DM) in the SBMs were both linearly and quadratically decreased as heating time increased (P < 0.05). The concentrations of sulfhydryl and total sulfhydryl in the SBMs were linearly decreased as heating time increased (P < 0.05).

4. The average daily gain was linearly decreased while the feed conversion ratio (FCR) was linearly increased in broilers as heating time of dietary HSBMs increased during both d 22–42 and d 1–42 of study (P < 0.05), though FCR of broilers during d 22–42 study were unaffected when the heating time of dietary HSBMs was 1 h (P > 0.05). The serum glucose concentration and the activity of trypsin at d 42, and the apparent total digestibility of CP and DM were all linearly reduced in broilers when heating time of dietary HSBMs increased (P < 0.05). However, 1 h HSBM has a numerical higher CP and DM digestibility than NHSBM. The serum urea nitrogen contents were both linearly and quadratically increased at both d 21 and 42 (P < 0.05), and relative pancreas weight was linearly increased at d 42 in broilers as heating time of dietary HSBMs increased (P < 0.05).