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Endogenous and exogenous fat digestion in growing pigs
The objective of this experiment was to compare the apparent total tract digestibility (ATTD) of endogenous fat (ether extract innate in ingredients; ENEE) versus fat added to the diet (EX) in formulations that contain increasing quantities of co-product ingredients. There were 5 dietary treatments: a corn soybean meal-based control diet (C-S) plus two pair of two diets each, with 1 of 2 levels of co-product inclusion per pair: (6 (LCP) or 12% (HCP) of each of corn DDGS, wheat middlings and corn germ meal), each with or without added soybean oil (SO). SO was added at 1.7% to the LCP or at 3.4% the HCP, respectively, to maintain constant NE relative to the C-S. Dietary treatments were fed during early growth (40 to 70 kg; GP) and late growth (70 to 110 kg; FP) periods. Diets with no added fat provided a baseline to calculate ENEE digestion. Then, within each pair of co-product diets (LCP and HCP), the ATTD of EX could be calculated by difference. Forty gilts (PIC 337 sires x Camborough product sows; initial BW=38.5±0.4 kg) were randomly assigned to diet, receiving feed and water ad-libitum. Total fecal collection was performed when pigs were transferred to metabolism crates at the end of GP (59.4±0.4 kg BW) and FP (95.8±0.8 kg BW). Data were analyzed using the MIXED procedure of SAS. In GP, ATTD of ENEE increased with the addition of co-products (29.6, 36.0, and 47.5%; for C-S, LCP and HCP respectively; P < 0.01). In FP, ATTD of ENEE also increased with the addition of co-products (36.0, 47.2 and 48.2%; for C-S, LCP and HCP respectively; P < 0.01). In GP, ATTD of total fat in the diet was 56.8% in LCP with 1.7% added fat and 69.8% in HCP with 3.4% added fat (P < 0.01). In FP, ATTD of total fat in the diet was 59.2% in LCP with 1.7% added fat and 69.4% in HCP with 3.4% added fat (P < 0.01). By difference, the ATTD of EX was 96.0% in LCP and 94.8% in HCP in the GP and 83.2% in LCP and 93.8% in HCP in the FP. In conclusion, fat added to the diet is much more highly digested than fat which exists naturally in the tested ingredients.
Keywords: fat digestibility, soybean oil, co-products