PSI-20 - Isobutyrate supplementation improved energy and nitrogen digestibility in prepubertal gilts fed a high insoluble, but not soluble, fiber diet

Abstract: Isoacids are short, branched-chain volatile fatty acids produced by microbial degradation of branched-chain amino acids. While there is a lack of information on isoacids supplementation in monogastric animals, in ruminants, isoacids are growth factors for cellulolytic bacteria which leads to improved digestibility of fibrous ingredients. The objective was to determine if feeding isoacids to prepubertal gilts could improve digestibility of high fiber diets. Two groups of 45 prepubertal gilts (139.10 ± 0.68 kg) were individually housed and allotted to 1 of 9 dietary treatments for a 28-day trial (n = 10 per treatment). Dietary treatments consisted of a 3 × 3 factorial arrangement with factors of diet type [corn-soybean meal (CSBM), CSBM with 40% inclusion of distiller’s dried grains with solubles (DDGS), or CSBM with 40% inclusion of sugar beet pulp (SBP)] and isoacids inclusion [no isoacid (NO), 0.50% inclusion of isobutyrate (IB), or 0.88% inclusion of an isoacid mixture (isobutyrate, 2-methylbutyrate, isovalerate; 1:1:1 ratio; MX). Isobutyrate inclusion was the same between IB and MX diets. Gilts were limit fed approximately 2.2 kg per day. Overall growth performance, apparent total tract digestibility (ATTD) of energy and nitrogen (N), and fecal volatile fatty acids (VFA) profile (d 26) were determined. Average daily feed intake (ADFI) was reduced and gain:feed ratio (GF) was increased in gilts fed DDGS (2.14 ± 0.07 kg/d and 0.20 ± 0.02 kg/kg, respectively) or SBP (2.07 ± 0.07 kg/d and 0.19 ± 0.02 kg/kg, respectively) compared to gilts fed CSBM (2.30 ± 0.07 kg/d and 0.15 ± 0.02 kg/kg, respectively), regardless of isoacids inclusion (P < 0.05). Gilts fed DDGS-IB had increased energy (86.5 vs. 83.5 ± 0.42%) and N (84.7 vs. 81.3 ± 0.85%) ATTD compared to gilts fed DDGS-NO (P < 0.05). Gilts fed CSBM-MX had reduced energy (86.9 vs. 88.3 ± 0.50%) and N (75.4 vs. 78.7 ± 0.39%) ATTD compared to gilts fed CSBM-NO (P < 0.05). Moreover, gilts fed SBP-NO had increased energy (85.9 vs. 83.6 ± 0.44%) ATTD compared to the other groups and increased N (71.8 vs. 67.2 ± 0.51%) ATTD compared to SBP-IB (P < 0.05). Fecal content of isobutyrate was decreased in NO compared to the other groups (2.10 vs. 3.00 ± 0.31 mM/L), while fecal content of heptanoate was increased in MX compared to NO (0.06 vs. 0.03 ± 0.01 mM/L), regardless of diet type (P< 0.05). Gilts fed SBP-MX had increased fecal content of total VFA compared to gilts fed SBP-NO (108.90 vs. 67.60 ± 11.50 mM/L; P < 0.05). These results suggest that IB may positively impact the digestibility of diets with a high content of insoluble fiber.