Effect Of Different Levels Of ADF Diets On Growth Performance,Intestinal Mucosal Immunity And Caecum Fermentation Of Weaning Rabbits

A single factor experiment was conducted to investigate the effect of dietary fiber(ADF) on the growth performance,intestinal mucosal immunity and caecum fermentation traits of growing rabbits. Sixty New Zealand rabbits weaned at 35±2d were allocated into.3 treatments in accordance with body weight, and there were 5 replicates each treatment. Three isoenergetic and isonitrogenous diets were formulated containing ADF 15%(low),20%(media) and 25%(high), respectively. The growth trail last 28 d. The slaughter trail was carried out when growth trial was finished, and the effect of different dietary ADF levels on intestinal development,mucosal immunity and caecum fermentation traits were analyzed. The results were showed as following:1) The growth performance of rabbits was significantly affected by dietary ADF level. The ADFI increased with increasing dietary fiber (P<0.01). The feed efficiency of media and low ADF diets were 17.4% and 14.6% (P<0.01) higher than that of high dietary ADF. The growth performance of media ADF diet was better than the other two treatments, and the diarrhea ratio was extremely decreased when the dietary ADF level increased (P<0.01) .2) The development of intestinal tract was promoted and the intestinal mucosal morphology was significantly affected by increasing dietary ADF. The stomach and caecum relative weight of media and high dietary ADF were higher than that of the low dietary ADF level (P<0.05) . The villous height of high and low fiber were strikingly decreased by 33.2% and 19.1% (P<0.01) compared with the media fiber, and the crept depth of high fiber was increased by 27.9% and 27.8%(P<0.01) .Hence, the villous height/crept depth was decreased by 68.8% and 41.7% (P<0.01) . The adverse effect of high fiber was greater than low fiber. High fiber decreased gastrointestinal tract content weight by promoting evacuation(P<0.05) and decreased small intestinal sucrase and maltase, therefore the decreased apparent digestibility of nutrients was observed.3) High fiber promoted the immune organ development and notably enhanced the secretion of cytokins and slgA. The absolute and relative spleen and thymus weight of media and high fiber were greater than low fiber (P<0.05) . The secretion of IL-2(P<0.01 )and sIgA(P<0.05)were promoted while the intestinal lymphocytes(IEL,LPL) number were increased by dietary fiber (P<0.05) .4) The caecum inner circumstance was significantly affected. Both of the pH value(P<0.05) and NH₃-N concentration (P<0.01) were increased with increasing dietary fiber. On the contrary, the TVFA concentration was decreased (P< 0.05) .The decreased butyric acid molar proportion was compensated by the increase of acetic acid when fiber increased. The fibrolytic enzymes were increased with increasing dietary fiber (P<0.01) .From the results showed above we can come to the conclusion that dietary ADF level could dramaticly affect the growth performance,gastrointestinal development,immune function,digestive enzymes activity and nutrients apparent digestibility of weaning rabbits. The gastrointestinal tract development and function could be improved and the diarrhea ratio could be reduced by increasing dietary ADF. Exorbitant dietary fiber decreased nutrients digestibility. There was a negative correlation between the decrease of diarrhea ratio observed and the increase of IL-2 and sIgA secreted.