Diets for pigs may vary in composition and in their concentration of the energy containing nutrients (i.e., protein, fat, starch and sugars, and dietary fiber). To our knowledge, however, there is no information on how concentration of net energy (NE) is affected by dietary starch and fiber concentrations in diets fed to group-housed pigs. Therefore, the objective of this experiment is to determine NE and nitrogen balance in diets containing various levels of starch and fiber fed to group-housed pigs.

Experimental design

Five diets contained corn and soybean meal and decreasing inclusion rate of corn distillers dried grains with solubles (i.e., 35% to 7%). An additional diet contained corn, soybean meal, and 10% corn starch to achieve a high starch and a low fiber concentration. Ratios between digestible amino acids and metabolizable energy (ME) in all diets were adjusted to meet requirements.

A total of 48 pigs (initial weight: 43.99 ± 8.38 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, each block provided 3 replicates per diet for a total of 6 replicates for each diet from the 2 blocks.

Pigs had ad libitum access to feed and water. 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 nitrogen. Concentrations of digestible energy (DE), ME, and NE, the ATTD of dry matter (DM) and GE, and nitrogen balance in diets were calculated.

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 dietary starch in diets.

Results

The ATTD of GE and DM was increased (quadratic; P < 0.05) by increasing starch and decreasing fiber in diets (Table 1). Concentration of DE in diets tended to be reduced (linear; P = 0.069), but ME and NE in diets tended to be increased (linear; P < 0.10) by increasing dietary starch and decreasing fiber. The ATTD of nitrogen and retention of nitrogen (% intake and % absorbed) were increased by increasing dietary starch (linear; P < 0.001). In conclusion, increasing starch and reducing fiber in diets increased digestibility and utilization of energy and nitrogen in group-housed pigs. Further research is warranted to determine energy digestibility and NE in diets containing varying levels of dietary fat and protein.

Key points

• The ATTD of GE and DM and concentration of NE is increased by increasing starch and decreasing fiber in diets fed to group-housed pigs.
• Digestibility and retention of nitrogen are increased by decreasing the inclusion of fiber feed ingredient in diets fed to group-housed pigs.

Table 1. Apparent total tract digestibility (ATTD) of dry matter (DM) and gross energy (GE), concentrations of digestible energy (DE), metabolizable energy (ME), and net energy (NE), and nitrogen (N) balance in diets fed to group-housed pigs¹

¹Least mean squares represent 4 to 6 replicates per dietary treatment.

²The last diet contained corn, soybean meal, and 10% corn starch.

³P-value for linear (L) and quadratic (Q) effects of increasing dietary starch.

⁴TDF = total dietary fiber.