Effects Of Pellet Diets With Different Concentrate-roughage Ratio On Growth Performance And Development Of Gastrointestinal Tract Of 3～6 Monthly Calves

This study was conducted to investigate the effects of pellet diets with different concentrate-roughage ratios on growth performance, rumen fermentation and development of gastrointestinal tract of calves. A total of 12 health weaned bull Holstein calves (days=103.92±1.5d; weight=121.25±4.12kg) were assigned randomly to 4 groups (Ⅰ, Ⅱ, Ⅲ, IV), with 3 calves in each group. The diets were isonitrogenous and isocaloric with four concentrate-roughage ratios (75:25,70:30,65:35,60:40). The experiment was conducted with 14d for adaptation and 56d for trial. The results were showed as follows:1. Effects of pellet diets with different concentrate-roughage ratios on growth performance, apparent nutrition digestibility, blood indices and the expression of GLUT1, FATP4 and PepTl mRNA in different tissues of calves were studied. The results indicated that, there was no significant difference in body weight gain, average daily gain, feed efficiency, body height, body length, heart girth and cannon circumference among the treatments(P>0.05). The apparent digestibility of CP、NDF in treatment Ⅲ was the highest, and significantly higher than that of treatment(P<0.05); The digestibility of ADF in treatment Ⅲ and IVwere significantly higher than that of treatment Ⅰ and Ⅱ (P<0.05). GLU concentration in treatment Ⅰ and Ⅱ were significantly higher than that of treatment Ⅲ and IV(P<0.05); the serum BUN concentration in treatment Ⅳ was the highest, and was significantly higher than that of treatment Ⅱ and Ⅲ(P<0.05). The serum T4 concentration in treatment Ⅳ was the lowest, and significantly lower than that of treatment Ⅱ(P<0.05); The serum INS concentration was the highest, and significantly higher than that of treatment Ⅱ (P<0.05). The expression of GLUT1, FATP4 and PepT1 mRNA in gut of group Ⅲ were higher, comparing with the others (P<0.05).2. Effects of pellet diets with different concentrate-roughage ratios on rumen fermentation, microbial synthesis and the quantities of rumen bacteria of calves were tested. The results indicated that, the total VFA and acetate concentration of treatment Ⅳ were the lowest, and significantly lower than those of treatment Ⅰ(P<0.05); butyrate level of treatment Ⅳ was higher than treatment Ⅰ and Ⅲ (P<0.05). Acetate:propionate ratio in group Ⅲ was the highest, and significantly greater than group Ⅳ(P<0.05). The abundance of Ruminococcus flavefaciens was increased in group Ⅲ, comparing with other treatments (P<0.05). The abundance of Ruminococcus albus, Butyrivibrio fibrisolvens, General fungi, Ruminobacter amylophilus, Lactobacillus and Ciliate protozoa in group Ⅳ were higher than other treatments (P<0.05).3. Effects of pellet diets with different concentrate-roughage ratios on development of gastrointestinal tract of calves were examined. The results indicated that, the rumen wall thickness of ventral sac and dorsal sac, and the papilla length on rumen dorsal sac of treatment Ⅳ were the highest, and significantly higher than that of treatment Ⅰ and Ⅱ (P<0.05). The rumen papilla width of ventral sac and the papilla length of ventral and dorsal sac were the highest, and significantly higher than that of treatment Ⅰand Ⅱ (P<0.05). The villus length on duodenum of treatment Ⅳ was the highest than the others (P<0.05). The mucous membrane thickness on duodenum in treatment Ⅲ and Ⅳ were significantly higher than that of treatment Ⅰ and Ⅱ (P<0.05). The villus length and the mucous membrane thickness on jejunum location in treatment Ⅲ and Ⅳ were significantly higher than that of treatment Ⅰ and Ⅱ (P<0.05). The villus length front and back of jejunum in treatment I were the lowest than other groups (P<0.05).To sum up, the pellet diets with 35%-40% roughage, was more favorable to improve nutrient digestibility and protein synthesis, and improve growth of microorganism and development of gastrointestinal tract.