Two weaning diets (C and S) and three weaning ages (21, 25, and 28 days) were compared in a two factorial arrangement to evaluate their effect on growth performance, body composition and caecal fermentation activity of young rabbits. One hundred litters born the same day from multiparous does were used. Sixty litters were early weaned at 21, 25 and 28 days of age (20 litters per weaning age), put in collective cages (nine kits per cage) (W21, W25, and W28 litters) and offered the control diet C (crude protein (CP) : 175 g/kg dry matter (DM); ether extract : 20 g/kg DM; starch : 157 g/kg DM; acid-detergent lignin (ADL) : 60 g/kg DM; digestible energy (DE) : 11·08 MJ/kg DM) or the starter diet S (CP : 173 g/kg DM; ether extract : 41 g/kg DM; starch : 112 g/kg DM; ADL : 51 g/kg DM; DE : 11·31 MJ/kg DM). At 32 days of age, 180 early weaned rabbits (three rabbits from each of the 60 litters above) were selected : 60 animals were slaughtered; 120 animals were placed into individual cages and offered a fattening diet (CP : 166 g/kg DM; ether extract : 23 g/kg DM; starch : 177 g/kg DM; ADL : 49 g/kg DM; DE : 11·26 MJ/kg DM) from 32 to 56 days of age. At 56 days of age, another 60 representative rabbits were slaughtered. The administration of diet S to the early weaned rabbits increased litter weight at 32 days (6160 v. 6027 g; P <005) and gain to food ratio from weaning to 32 days (752 v 666 g/kg; P <0001) compared with diet C. Moreover, empty bodies (EB) of S rabbits were fatter (fat : 45 v. 41 g/kg; P = 001) and had greater energy content (5·92 v 5·71 MJ/kg; P <001). At 56 days of age, no residual effect of the diet was recorded. Weaning age affected growth performance, body composition and caecal fermentation at 32 days of age : EB weight (P <005) and EB protein concentration increased (from 164 to 168 g/kg, P <0·01) while caecal volatile fatty acid concentration decreased (from 71·7 to 53·8 mmol/l; P <0·01) when weaning age was increased from 21 to 28 days. At 56 days of age, no effect (P > 0·05) of weaning age was recorded on growth performance or caecal fermentation traits, but EB protein remained lower in the earliest weaned rabbits (P <0·05). In conclusion, feeding a high-fat low-starch diet to early weaned rabbits stimulated growth and body fat and energy retention of kits at 32 days of age with no effect on caecal fermentation. The early weaning successfully performed at 21 days of age strongly stimulated caecal fermentation but reduced body protein reserves.

The effect of the weaning diet on the subsequent colonic metabolism of bran and pectin in the adult rat has been investigated. Feeding a fibre-reduced diet on its own or supplemented with bran (WB) and pectin (P) from weaning (fibre-reduced (weaning)) was compared with introducing the same diet to age-matched rats reared on a standard laboratory diet from weaning (fibre-reduced (6 weeks)). The effects of the diets on colonic metabolism were measured by wet and dry caecal contents and stool weights, caecal sac weight, and caecal and faecal short-chain fatty acids (SCFA). Final body-weights were greater for fibre-reduced (6 weeks) and fibre-reduced (6 weeks)+P groups, but not fibre-reduced (6 weeks)+WB, than those of the fibre-reduced (weaning) rats. Rats fed on fibre-reduced (6 weeks) diet had a higher total caecal SCFA content than fibre-reduced (weaning) control rats. Fibre-reduced (weaning)+P-fed rats had a threefold higher caecal concentration of both propionate and butyrate than the matched fibre-reduced (6 weeks)+P group. Fibre-reduced (weaning)+WB animals had a significantly higher butyrate caecal concentration compared with their matched fibre-reduced (6 weeks)+WB group. Fibre-reduced (weaning)+P-fed rats had a lower faecal output than the fibre-reduced (6 weeks)+P rats. There was no difference in faecal output in rats fed on either fibre-reduced (6 weeks)+ WB or fibre-reduced (weaning)+WB. The faecal concentration of SCFA was in general higher in the rats fed on fibre-reduced (weaning) alone, +P, or +WB than in those fed on fibre-reduced (6 weeks) alone, +P or +WB. Faecal output of total and individual SCFA was increased on the fibre-reduced (weaned)+WB diet compared with fibre-reduced (6 weeks)+WB-fed animals. The diet at weaning may be important in determining the pathways of caecal bacterial metabolism in the adult rat. In studying the effect of a dietary fibre on caecal metabolism and faecal output, when the diet is changed appears to be important