There is considerable concern about the true net energy value that should be assigned to apparently digested energy in diets where a substantial proportion of the substrates are fermented in the gut. Experiments involving both digestibility and growth trials were undertaken to compare the growth supporting properties of apparently digested energy, arising either from fermentation or enzymic hydrolysis. Dried unmolassed sugar beet pulp (SBP) and maize starch (MS) were used as models for fermentation and enzymic hydrolysis respectively.

In the first phase, sixty estimates of digestibility were made with 10 female and 20 castrated male growing pigs. There were five diets, a control (C), and two concentrations of maize starch (100 and 200 g/kg) and two of sugar beet pulp (150 and 300 g/kg). The composition and chemical analysis of the five diets are presented in Table 1 . The pigs were housed in metabolic cages during the trials and female pigs had catheters in the urinary bladder. Collections were made over 10 days following a 7-day preliminary period. In the growth studies, 40 pigs (20 female and 20 male castrates) were allocated randomly to the same five diets.