Selection of Pigs for Lean Gain When Fed High Fiber Diets to Improve Fiber, N, and Energy Digestibility and Digestive Tract Characteristics

The objective of this study was to determine the impact of high fiber diet and genetic line, developed using either a low or high fiber diet, on digestibility of fiber, N, and energy and digestive tract characteristics. Barrows (n=32; 50.4±3 kg) were used in a 14 d metabolism study with a 2x2 factorial design with genetic line (high fiber selected and control selected lines) and diet (high fiber or control) as factors. Genetic lines were selected for lean growth over 3 generations while consuming the high fiber or control diets. Barrows were separated into 2 replicate groups of 16 consisting of 4 littermate pairs from each genetic line. Diets were randomly assigned within littermate pairs. High fiber diets were formulated to include 15% of each DDGS, wheat middlings and soy hulls and control diets were corn-soybean meal based. Diets were formulated to contain equal SID lysine to net energy ratios (0.93 and 0.82% SID lysine and 2,484 and 2,187 kcal/kg NE for control and high fiber diets, respectively). Pigs had ad libitum access to feed for an 11 d adaptation period and were restricted to 90% ad libitum on d 12, 13, and 14 while fecal samples were collected to determine digestibility of ADF, NDF, N, and energy, using titanium dioxide as indigestible marker. Total transit time was measured by feeding a color marker (chromic oxide) and recording time until first fecal appearance of marker. Pigs were euthanized on d 14, pH was measured in the ileum and cecum along with cecum weights. Data were analyzed using MIXED procedures of SAS. There were no interactions between diet and genetic line (P>0.05). Digesta transit time, cecal and colon pH were not impacted by diet. No effects of genetic line on digesta pH or digestibility were observed. High fiber genetic selection tended to increase (P=0.09) digesta transit time (1,704.4 vs. 1,521.3±75.5 min). Pigs fed high fiber diets had increased (P<0.05) ileal pH (6.61 vs. 6.32), ADF (56.3 vs. 41.7%) and NDF digestibility (61.0 vs. 41.6%), and had decreased (P<0.05) N (77.8 vs. 84.5%) and gross energy (GE) digestibility (78.3 vs. 84.2%). Genetic selection for lean gain of pigs when fed high fiber diets increased total transit time, but did not impact digestibility. Feeding high fiber diets decreased N and GE digestibility while increasing ileal pH and fiber digestibility, regardless of whether pigs had been selected on high fiber diets or not.