Interactive effects among fiber and fat sources on energy and fat digestion in 53- to 74-kg pigs

An experiment consisting of two groups of 60 pigs was conducted to determine interactive effects between fiber source, fat source, and week of fecal sampling on apparent total tract digestibility (ATTD) of dry matter (DM), ether extract (EE), gross energy (GE), and total dietary fiber (TDF) in 53- to 74-kg pigs. Diets were formulated based on corn-soybean meal (CSBM, 15.4% TDF) or a CSBM diet with 35% distillers dried grains with solubles (DDGS, 20.6% TDF), 15% soybean hulls (SH, 23.0% TDF), or 30% sugar beet pulp (BP, 28.4% TDF), in combination with no added fat, 10% tallow (TL), or 10% soybean oil (SO). Feces were collected on d 7, 14, and 21 to determine ATTD of DM, EE, GE, and neutral detergent fiber (NDF). There were no significant week × diet × fat, week × diet, or week × fat interactions noted (P > 0.10) for any parameter measured; there was, however, a diet × fat interaction (P ≤ 0.01) and week effect (P ≤ 0.01) for each parameter measured. Adding 10% TL increased the ATTD of EE in pigs fed the CSBM- and BP-based diets more than in pigs fed DDGS- or SH-based diets with added TL. In contrast, adding 10% SO increased the ATTD of EE in pigs fed CSBM-, SH-, and BP-based diets more than in those fed the DDGS-based diet with added SO. Adding 10% TL increased ATTD of NDF in the pigs fed the CSBM- and SH-based diets to a greater degree compared to pigs fed the DDGS- or BP-based diets with added TL, while adding 10% SO increased ATTD of NDF in pigs fed the CSBM-, DDGS-, and SH-based diets to a greater degree compared to pigs fed the BP-based diet with added SO. The ATTD of GE was difficult to interpret and did not always correspond with the changes noted in the ATTD of EE and NDF. In general, GE digestibility was improved by supplementing TL to the low-fiber CSBM diet, had little effect when added to the insoluble fiber diets (i.e. DDGS or SH), but had a negative effect when supplemented to the BP-based diet. In contrast, ATTD of GE increased with SO inclusion in all diets, but to a greater extent in CSBM-, DDGS-, and SH-based diets compared to diets containing BP. Overall, the data indicated that fat digestibility is reduced more by feedstuffs with a high degree of insolubility (DDGS or SH) compared to a feedstuff with a high degree of solubility (BP). In addition, data from this experiment suggest that fat type interacts with fiber type and that the reduction in fat digestion is greater when a saturated fat is added to the diet compared to unsaturated fat sources.