Effects Of Heated Soy Protein Isolate On Digestive Function Of Broilers And Regulatory Effects Of Vitamin E And Lipoic Acid

The study was conducted to investigate the effects of heated soy protein isolate (HSPI) on the digestive function of broilers, and the regulatory effects of vitamin E (VE) and lipoic acid (LA) on the digestive function of broilers fed diets containing HSPI were studied. The study included three trials as follows:The first study was conducted to investigate the effects of HSPI on digestive function of broilers. A total of 320 one-day-old Arbor Acres broiler chicks were randomly divided into 4 groups with 8 replicates of 10 birds. Birds were fed diets containing native SPI (Control), or containing the same amount of SPI heated in an oven at 100℃ for 1,4, and 8 h, respectively, for 21 days. Compared to the control group, average body weight gain (ABWG) and average feed intake (AFI) of broilers fed diets containing HSPI for 8 h were significantly decreased at 21 d (P<0.05). Serum urea nitrogen (UN) was increased in the broilers fed diets containing SPI heated for 4 and 8 h when compared with that in the control group at 21 d (P<0.05). In contrast, serum glucose (GLU) was decreased by all HSPI at 21 d (P<0.05). Relative liver weight in all HSPI groups was lower than that in the control group at 14 d, however, relative pancreatic weight in all HSPI groups was higher than that in the control group at 21 d (P<0.05). And relative weights of anterior intestine and ileum decreased in broilers fed a diet containing SPI heated for 8 h in comparison with those in the control group at 21 d (P<0.05). Birds fed diets containing SPI heated for 4 and 8 h decreased lipase activity in anterior intestinal content as compared with the control at at 14 (P<0.05), and lipase activity in anterior intestinal content in all HSPI groups was lower than that in the control group at 21 d (P<0.05) Amylase, protease and trypsin activities in anterior intestinal content were decreased in broilers fed diet containing SPI heated for 8 h compared with the control group at 21 d (P<0.05). The apparent digestibility of dry matter (DM) from 8 to 10 d decreased in broilers fed diets containing SPI heated for 8 h when compared with that in the control group (P<0.05), and the same effects were also noted for the apparent digestibility of DM, crude protein (CP), and ether extract (EE) in broilers fed a diet containing SPI heated for 8 h from 15 to 17 d (P<0.05).The second study was conducted to investigate the effects of HSPI on pancreatic function of broiler chickens. Experiment design was the same as that of Trial 1. The results showed that no significant differences were noticed for measured parameters of pancreatic function of broilers fed diets containing HSPI when compared with the control group at 14 d (.P>0.05). The activities of protease and trypsin in pancreas were lower in broilers fed diets containing SPI heated for 8 h than those in the control group at 21 d (P<0.05). Broilers fed the diet containing SPI heated for 8 h exhibited a decrease in total antioxidant capacity (T-AOC) (P=0.058) and catalase (CAT) (P=0.064) activity compared with the control group at 21 d. Malondialdehyde (MDA) content of birds fed the diet containing SPI heated for 8 h was higher than that in the control group at the same time (P<0.05). In addition, a tendency toward an increase in glutathione disulphide (GSSG) content (P=0.065) and a decrease in glutathione reductase (GR) activity (P=0.061) in birds fed the diet containing SPI heated for 8 h were observed at 21 d. Birds fed diets containing SPI heated for 4 and 8 h showed a significant decrease in reduced glutathione (GSH):GSSG ratio (P<0.05), and glutathione peroxidase (GPX) activity in birds fed diet containing SPI heated for 8 h was significantly lower than that in the control group at 21 d (P<0.05).The third study was conducted to study the effects of VE and LA on digestive function of broilers fed diets containing HSPI. A total of 300 one-day-old Arbor Acres chicks were randomly divided into 5 groups with 6 replicates of 10 birds. Birds were fed native SPI diet (Control), or HSPI diet and HSPI diets containing 200 mg/kg VE, LA, and VE+ LA respectively, for 21 days. The results showed that no significant differences were noticed for measured parameters of digestive function of broilers in all groups at 14 d (P>0.05). Compared to the HSPI group, adding VE and VE+LA could significantly increase ABWG, and ABWG in LA supplementation group was relatively higher, and adding VE could also significantly increase AFI. Serum UN content increased and GLU content decreased in the broilers fed HSPI diet when compared with that in the control group at 21 d (P<0.05). Adding VE+LA could decrease the UN content (P=0.097), and adding LA and VE+LA could increase the GLU content (P>0.05). The relative pancreas weight was higher, however, relative weight of liver was decreased in broilers fed HSPI diet in comparison with the control group at 21 d (P<0.05). Adding VE+LA could decrease the relative pancreas weight (P>0.05). Amylase, lipase and trypsin activities in anterior intestinal content were decreased in broilers fed HSPI diet compared with those in the control group at 21 d (P<0.05). Adding LA and VE+ LA could increase the amylase and lipase activities in anterior intestinal content (P>0.05). Adding VE and VE+LA could increase the trypsin activity in anterior intestinal content (P>0.05). Amylase and trypsin activities in anterior intestinal content were decreased in broilers fed heated HSPI diet compared with those in the control group at 21 d (P<0.05). Adding VE+LA could increase the amylase and trypsin activities in anterior intestinal content (P>0.05). Broilers fed HSPI diet exhibited a decrease in T-AOC and an increase in MDA content compared with that in the control group at 21 d (P<0.05). Adding VE+ LA could increase the T-AOC and adding VE, LA, and VE+LA in the HSPI diet could decrease the MDA content (P>0.05). Birds fed HSPI diet showed a significant decrease in GPX, GR activities and GSH:GSSG ratio (P<0.05) compared with the control group at 21 d (P<0.05). Adding VE in the HSPI diet could increase the GPX (P=0.060) and GR activities (P>0.05). Adding VE+LA could increase the GSH/GSSG ratio (P=0.082) and the GPX activity (P>0.05).In conclusion, these results indicated that HSPI can exert a negative influence on the growth performance and digestive function of broiler chickens. Adding VE or LA can exert a beneficial influence on the growth performance and digestive function of broilers fed HSPI diets to a certain degree. Adding VE can alleviate the growth performance preferably, while adding VE in combination with LA can alleviate the digestive function preferably.