The present study was undertaken to provide detailed information about the effect of dietary fibre (DF)
level on the development of the digestive tract, on nutrient digestibility and on energy and protein
metabolism of pigs housed in low (13') or high (23") thermal environments. Low- and high-fibre diets (59
v. 268 g DF/kg DM) were studied in three balance periods with fktulated pigs in the weight range
45-120 kg. Heat production was measured using open-circuit respiration chambers. Pea fibre and pectin
were used to adjust the DF level in the high-fibre diet. Per kg empty body weight the stomach, caecum
and colon and the length of colon were significantly greater in pigs consuming the high-fibre diet than
in those on the low-fibre diet. Pigs kept at low temperature had significantly heavier caecums than those
kept at the high temperature. Digestibilities of protein, DM and energy were lowest for the high-fibre
diet. Only minor amounts of NSP and its constituent sugars were degraded anterior to the ileum, whereas
in the hind-gut the fermentation of the total NSP fraction was high, being 0.77 for the high-fibre diet and
0.59 for the low-fibre diet. Feeding the high-fibre diet increased the flow of digesta through the terminal
ileum %-fold and an extra 460 g organic matter was fermented daily in the hind-gut compared with pigs
fed on the low-fibre diet. The amount of retained energy as a proportion of metabolizable energy
decreased in relation to the amount of energy fermented in the hind-gut. Based on the present data it was
estimated that the relative value of energy derived from hind-gut fermentation was 0.73 in comparison
with energy enzymically digested in the small intestine. There was negligible effect of the temperature
-fibre interaction on energy metabolism. However, it could be calculated that the decrease in
temperature from 23" to 13" was associated with an increase in heat production by 2.9 MJ/pig per d.