Abstract The objective was to determine net energy (NE) and nitrogen (N) balance in growing pigs fed diets containing varying levels of dietary fiber. Five diets contained corn and soybean meal and increasing inclusion rate of soybean hulls (i.e., 0, 6, 12, 18, 24, or 30%). Ratios between digestible amino acids and metabolizable energy (ME) in all diets were adjusted to meet requirements. Forty-eight pigs (initial weight: 39.58 ± 3.39 kg) were used in two blocks of 24 pigs. The 24 pigs were assigned to 6 calorimeter chambers with 4 pigs per chamber. Chambers in each block were allotted to a 6 × 3 incomplete Latin square design with 6 diets and 3 periods. Therefore, there were a total of 6 replicates for each diet. Pigs had ad libitum access to feed. Diets were fed for 13 days in each period. After a 7-day adaptation period, O2 consumption and CO2 and CH4 productions were measured for 6 days to calculate total heat production. Fecal and urine samples were quantitatively collected for 6 days and analyzed for gross energy (GE) and N. The statistical model included diet as fixed effect and group, period, and chamber as random effects. Contrast coefficients were used to determine the linear and quadratic effects of increasing soybean hulls in diets. Results indicated that daily feed intake was not affected by dietary treatment (Table 1). Weight of orts and feces increased (linear, P 0.05) by increasing soybean hulls in diets, which decreased (linear, P 0.05) the apparent total tract digestibility (ATTD) of dry matter and GE and digestible energy in diets. Urine GE excretion tended to decrease (linear, P = 0.051) and ME in diets decreased (linear, P 0.001) as soybean hulls increased in diets. Total heat production and retained energy did not change, but respiratory quotient in the fed state and NE decreased (linear, P 0.05) as soybean hulls increased in diets. Ratios between ME and GE and NE and GE decreased (linear, P 0.01) by increasing soybean hulls in diets. Nitrogen intake decreased (linear, P 0.05), but fecal nitrogen excretion increased (P 0.001) as soybean hulls increased in diets. The ATTD of nitrogen, absorbed nitrogen, and retained nitrogen decreased (linear, P 0.01), but urine nitrogen excretion was not affected by dietary fiber. In conclusion, increasing dietary fiber from soybean hulls reduced the ATTD of GE and NE in diets fed to group-housed pigs. The ATTD of nitrogen was reduced by increasing soybean hulls, but retention of nitrogen was not affected. Results from this experiment may be used in the development of prediction equations for NE in diets and feed ingredients fed to pigs.
Lee et al. (Wed,) studied this question.