effect of age on Bacterial fibrolytic activity 
of caecal flora of rabbit 
V Pinheiro1, T. Gidenne2 , L. Falcão e Cunha3. 
1 DZ, UTAD, Vila Real, Portugal; 2 - SRC, INRA, Toulouse, France; 3 - DPA, ISA, Lisboa, Portugal.

As a monogastric herbivorous animal, the rabbit exhibits a digestive physiology adapted to high intake of dietary fibre, which is fermented in the hindgut. The capacity to digest fibre is developing when the animal starts to eat solid feed. However, information about the increase of bacterial fibrolytic activity is very scarce. Thus, we studied the effect of age (6, 10 and 25 weeks) on bacterial fibrolytic activity (BFA) of caecal flora.
Three experimental diets were formulated with common ingredients (Pinheiro and Gidenne, 2000). Feeds contained similar concentrations of starch (20%), crude protein (17%) and fibre, and a similar ratio digestible protein/digestible energy. Diets were given ad libitum in pelleted form (3.5mm diam.). BFA was measured on soft faeces, collected after ten days of diet adaptation. After sonication of samples of caecotrophes, the fibrolytic enzymes were extracted from bacteria according to Jehl et al. (1996). Cellulolytic, xylanolytic and pectinolytic activities were measured after incubation of enzyme preparation with a substrate: carboxymethyl cellulose, birchwood xylan, citrus pectin. BFA was expressed in mmol of reducing sugars released per h and per g of dry soft faeces. As there is no interaction between the effect of age and the effect of diets, we presented only results of BFA according to age.
The BFA in soft faeces was significantly increased in adult (Fig.1), compared to growing rabbits. The pectinolytic activity was more affected (+80%; P<0,01). The xylanolytic activity increased by 50% (P<0,01), and the cellulolytic activity was not affected by the age. In growing rabbits, the BFA did not differ between 6 and 10 wks of age.

Figure 1 : Bacterial fibrolytic activity of caecal flora of rabbit according to age

According to our results the digestive potential of the caecum globally increased with age. Unlike to our work, Marounek´s et al., (1995) results showed a decrease of cellulase activity and a maintenance of xylanase activity with the age. On both works, age effect on pectinolytic activity was similar, though the increase was more pronounced in present results. The activity of cellulase was low. This finding is consistent with a rather low digestibility of this fibre fraction, observed in rabbit. The high digestibility of pectic substances (73%) found by Gidenne et al. (1991), could correspond with the presence of highly active pectinase.

Références : Jehl, N., Gidenne, T., Le Roux, J.F., 1996. Measurement of the bacterial fibrolytic activity in the caecum and in the soft faeces of the rabbit. 6th World Rabbit Congress, 9-12 July, France., Vol. 1, 199-203.
Gidenne, T., Carré, B., Ségura, M., Lapanouse, A., Gomez, J., 1991. Fibre digestion and rate of passage in the rabbit: effect of particle size and level of lucerne meal. Anim. Feed Sci. Technol. 32, 215-221.
Marounek, M., Vovk, S.J., Skrivanova, V., 1995. Distribution of activity of hydrolytic enzymes in the digestive tract of rabbits. Br J. Nutr. 73, 463-469. 
Pinheiro, V., Gidenne, T., 2000. Substitution of wheat by potato starch for growing rabbits: effect on performances, digestion and health. 7th World Rabbit Congress, july 2000, Spain, vol. C, p. 391-399.