EFFECTS OF DIETARY FIBER SOURCES ON VOLATILE FATTY-ACID PRODUCTION, INTESTINAL MICROFLORA AND MINERAL BALANCE IN RABBITS

An experiment was conducted to evaluate the effect of alfalfa hay meal (AHM), olive pulp meal (OPM) and grape pulp meal (GPM) on volatile fatty acid (VFA) production, intestinal flora and mineral balance in rabbits. Eighteen New Zealand White rabbits, 45 days of age, were used. The sources of fiber were fed at the 28% level in a practical diet for a 33 day period. The samples of AHM, OPM and GPM contained 409 g kg-1, 556 g kg-1 and 593 g kg-1 neutral detergent fiber (NDF) in the dry matter, respectively. Liveweight was not affected by dietary fiber, but feed intake showed significant differences (P < 0.05). An increase in the pH value of cecal digesta was observed in animals fed the AHM diet compared with those fed GPM (5.72 vs. 6.06). The total VFA concentrations were higher for both OPM and GPM diets than for the AHM diet (153 mM l-1 and 151 mM l-1 vs. 65.6 mM l-1). The proportion of acetate in the total VFA was higher (P < 0.05) and that of the propionate lower (P < 0.05) in the AHM group than in the OPM and GPM groups. Valerate was not detected in the cecal contents of rabbits fed the OPM or GPM diets. High counts of aerobic bacteria and faecal streptococci were presented in the cecum of the OPM group. Dietary fiber source affected the count of staphylococci. Sulfite-reducing clostridia increased in the ileum and cecum content of both OPM and GPM groups. Slight differences were observed in the numbers of coliforms and lactic acid bacteria in the intestinal content of the rabbits. The absorption of Ca, P and K was higher (P < 0.01) in the AHM group. Mg and Zn were less well absorbed (P < 0.01) in the GPM group. Low levels of Fe and Mn absorption (P < 0.05 and P < 0.01, respectively) were obtained in rabbits fed the OPM diet. An increase in Cu absorption (P < 0.01) was found in the OPM group. Fiber sources did not influence Ca and Fe balance. The P balance was higher (P < 0.05) in the AHM than in the GPM group.The AHM diet showed the lowest Mg and K balance (P < 0.01). The Cu and Zn balance was lower in the GPM than in the AHM and OPM groups (Cu, 0.13 mg day-1 vs. 0.45 mg day-1 and 0.33 mg day-1; Zn, -0.97 mg day-1 vs. 0.47 mg day-1 and 0.04 mg day-1, respectively). Except for K, no effect of fiber source could be detected in plasma mineral levels.