Effects Of Dietary Yeast β-glucan On Growth Performance And Gastrointestinal Development In Pre-ruminant Calves

In these series of research, pre-ruminant calves were used as animal models to study the effects of yeastβ-glucan on growth performance and gastrointestinal characteristics. The present research consists of three experiments which were listed as follow:Experiment 1: Effects of yeastβ-glucan on growth performance, nutrients digestibility, serum biochemical and gastrointestinal characteristics in pre-ruminant calves.In this experiment, 42 neonatal healthy Holstein calves were allotted to six groups and each group was fed with a diet supplemented with yeastβ-glucan at the dosage of 0,25,50,75,100,200 mg/kg, the whole experiment lasted for 56 d. The metabolism trial was conducted between 14-20 d, 42-48 d. Three calves of each group were slaughtered on the ending of experiment. The results showed that the ADG of the calves treated with 75 mgβ-glucan/kg in each period and the whole period was significant higher than that in the control group (P<0.05). Compared with the control group, the ratio of feed to gain (F/G) was higher (P<0.05) in the calves given 75 mgβ-glucan/kg, and the incidence of diarrhea was decreased (P<0.05) by 50 or 75 mgβ-glucan/kg. The apparent digestibility of DM, CP, EE and P in the 75 mgβ-glucan/kg group were significant higher than the control group (P<0.05). Compared with it in the control group, the concentration of ALB in the 75 mg/kg group was significantly decreased (P<0.05). As for the IgG and IgM in the 75 mg/kg groups, they were significantly increased than them in the control group on 14 and 42 d (P<0.05). Compared with it in the control group, the ALP of 75 mg/kg group was increased on 14, 28 and 42 d. The ratio of villous height to crypt depth (V/C ratio) was increased (P<0.05) in the calves treated with 75 mgβ-glucan/kg. Whenβ-glucan supplemented at the dosage of 75 mg/kg in diet, the number of Escherichia coli in rectum was significantly decreased compared with the control group (P<0.05), and the number of Lactobacillus was significantly higher than other groups (P<0.05). It could be concluded that dietary yeastβ-glucan added to the diet at 75 mg/kg could improve the development of the gastrointestinal tract, enhance the immune response and reduced the incidence of diarrhea in pre-ruminant calves, which improved nutrient absorption and at last improve the growth performance of pre-ruminant calves.Experiment 2: Bacteriostasis experiment of yeastβ-glucan on Escherichia coli in vitroIn this experiment, one object is to study the bacteriostasis of yeastβ-glucan and bacitracin zinc on Escherichia coli was measured by the plate counting method and the initial pH of culture medium were 6, 7 and 8. The other object is to study the bacteriostasis of yeastβ-glucan on Escherichia coli under the condition of the medium combined with Lactobacillus or its metabolites. The results showed that the number of Escherichia coli was significant lower in the group which supplemented with yeastβ-glucan when the pH of medium were 6 and 7 (P<0.05). When the pH of medium were 8, the number of Escherichia coli was significant lower in the group which supplemented with yeastβ-glucan than the control group after 6 h (P<0.05). The number of Escherichia coli was significant lower in the group that supplemented with yeastβ-glucan and bacitracin zinc, it was especially lower when the pH of medium were 7 and 8 (P<0.05) after 15 h. The variation of pH was the same with the number of Escherichia coli. The number of Escherichia coli in the group that contained Lactobacillus and yeastβ-glucan was significant lower than the control group before 9 h (P<0.05). The variation also occurred in the group that contained Lactobacillus metabolites and the variation of pH was the same with the variation of the number of Escherichia coli. It could be concluded that yeastβ-glucan had different degree of bacteriostasis on Escherichia coli under different initial pH by the plate counting method. Yeastβ-glucan could enhance the bacteriostasis of Lactobacillus or its metabolites on Escherichia coli.Experiment 3: Effects of yeastβ-glucan and bacitracin zinc on the growth performance, nutrients digestibility and gastrointestinal characteristics in pre-ruminant calves challenged with Escherichia coli K99.In this experiment, 20 healthy Holstein neonatal calves were randomly allotted to four groups. The calves were fed with a diet supplemented with 0 (Treatment A), two 75 mg yeastβ-glucan/kg (Treatment B and C), 60 mg bacitracin zinc/kg (Treatment D) of feed. The experiment lasted for 28 days. On d 21, the calves of Treatments A, B and D were challenged orally with Escherichia coli (O141:K99), with Treatment C fed normally. The metabolism trial was conducted between 18-20 d, 24-26 d. Three calves of each group were slaughtered on the ending of experiment. The result showed that Compared with Treatment A, ADG of the calves in Treatment B, C and D were significant higher before the Escherichia coli challenged (P<0.05), and ADG in Treatment B and D were increased by 30.4 and 30.8% after the Escherichia coli challenged (P<0.05). F/G in Treatment B, C and D were lower than that in Treatment A. Pre and post the challenge, the fecal score of treatment B and D were significant lower than the treatment A (P<0.05). The apparent digestibility of DM in B, C and D treatment during 18-20 d were 72.36, 72.59 and 73.89% which was significant higher than the control treatment (P<0.05). The apparent digestibility of CP in B and C treatment during 18-20 d were 83.17 and 87.37% which was significant higher than the control treatment of 76.11% (P<0.05). The apparent digestibility of EE was very high during the two period and there was no significant difference between each treatment (P<0.05). The weight of liver in the treatment B and D was significant lower than the control treatment and the bacitracin zinc (P<0.05), which decrease 7.31 and 5.94%. Compared with the control treatment, the rumen papilla height and width of yeastβ-glucan were significant higher than the control treatment (P<0.05). The villus height of duodenum in treatment B, C and D were not different (P>0.05), the crypt depth of duodenum in treatment C and D were significant lower than the control treatment and the treatment D (P<0.05), the v/c in treatment B, C and D were higher than the control treatment (P<0.05). The count of Escherichia coli in the rectum was increased (P<0.05) after the challenge in 12 h and 24 h, the count of Escherichia coli in the rectum in the calves from Treatments B and D were decreased (P<0.05), and the count of Lactobacillus was decreased in the calves from Treatment D (P<0.05) when compared with Treatment A. PCR-DGGE DNA profiles of 16S rDNA of microbiotics in the rectum indicated that the band number in treatment B and C were significantly higher than that in control treatment A and treatment D (P<0.05), which means that the multiplication of bacillus was higher than the control treatment A and treatment D . The degree of similarities of treatments was range from 50 % to 75 %. It could be concluded that yeastβ-glucan could erase the decrease of growth performance and nutrients digestibility of pre-ruminant calves, protect them from the injury of intestinal mucosa and modulated the population of intestinal microflora of pre-ruminant calves which challenged with Escherichia coli K99.