Dietary isoacids effects on growth, nitrogen, and energy digestibility, and fecal volatile fatty acids and microbial ecology in finishing pigs

Authors: Kerr, Brian; Anderson, Christopher; Pearce, Sarah; SCHWEER, WESLEY - Zinpro Corporation

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/30/2024
Publication Date: 7/1/2024
Citation: Kerr, B.J., Anderson, C.L., Pearce, S.C., Schweer, W.P. 2024. Dietary isoacids effects on growth, nitrogen, and energy digestibility, and fecal volatile fatty acids and microbial ecology in finishing pigs. Journal of Animal Science. 102. https://doi.org/10.1093/jas/skae170.
DOI: https://doi.org/10.1093/jas/skae170

Interpretive Summary: Isoacids, also known as branched-chain fatty acids, are branched ketoacids that include isobutyric, isovaleric, valeric, and 2-methylbutyric acid. Isoacids are mainly produced during the fermentation of branched-chain amino acids in ruminants and have been shown to enhance the growth of fiber-digesting organisms and are used in the biosynthesis of valine, leucine, and isoleucine. The current study was conducted to determine the ability of dietary isoacid supplementation in finishing pigs to improve nutrient digestion. The experiment conducted herein indicated there was little to no effect of isoacid addition on the microbiome, colonic volatile fatty acid concentrations, digestibility of energy or nitrogen, or on pig performance, but an improvement in the digestibility of energy and nitrogen in pigs fed diets containing dried distillers’ grains with solubles when isobutyrate was observed warranting further investigation. Data from this experiment provides information to nutritionists at universities, feed companies, and swine production facilities on the limited ability of isoacid addition to affect nutrient digestibility and animal performance.

Technical Abstract: Isoacids are branched ketoacids which when fed to ruminants have been shown to enhance the growth of fiber-digesting organisms and used for the biosynthesis of valine, leucine, and isoleucine. Although amino acids are not absorbed from the hindgut of pigs, hindgut fermentation can be extensive in finishing pigs and gestating sows such that the potential for isoacids to improve hindgut fermentation is of interest. Ninety finishing gilts were individually fed 1 of 9 dietary treatments consisting of diet type: corn-soybean meal (CSBM), a CSBM diet containing 40% distillers dried grains with solubles (DDGS), or a CSBM diet containing 40% sugar beet pulp (SBP); in combination with either no feed additive (CNT), the addition of 0.50% isobutyrate (IB), or the addition of a 0.88% mix of isobutyrate, isovalerate, and 2-methylbutyrate (MX) in place of corn. Gilts were limit fed approximately 2.2 kg per day for 28 d. On d 26, fresh fecal samples were collected for determination of apparent total tract digestibility (ATTD) of gross energy (GE) and nitrogen (N), determination of colonic volatile fatty acids (VFA), and evaluation of microbial ecology. There was no interaction between diet type and isoacid addition, and no main effect of isoacid or diet type on alpha or Shannon microbial diversity measures (P > 0.05). There was no interaction between isoacid addition and diet type, and no main effect of isoacid addition on microbial beta diversity (P > 0.05), but differences were observed in microbial beta diversity due to diet type (P = 0.05). There was no interaction between diet type and isoacid addition observed in colonic VFA concentrations (P > 0.05), with only minor differences in colonic VFA concentrations noted due to isoacid addition (P = 0.05). The interaction between diet type and isoacid addition on ATTD of dietary GE and N (P = 0.01) was largely because the addition of IB did not affect ATTD of GE or N in pigs fed the CSBM diet, but increased ATTD of GE and N in pigs fed diets containing DDGS and decreased the ATTD of GE and N in pigs fed diets containing SBP. In contrast, adding a blend of isoacids (i.e., MX) reduced the ATTD of GE and N, regardless of diet type. There was no interaction between diet type and isoacid addition, and no effect of isoacid addition was observed on pig performance (P > 0.05). Diet type did not affect ADG (P > 0.05), but pigs fed diets containing DDGS or SBP consumed less feed (P = 0.01) and exhibited greater GF ratios compared to pigs fed the low-fiber CSBM diet (P = 0.05). In conclusion, there was little to no effect of isoacid addition on microbial ecology, colonic VFA concentrations, ATTD of GE or N, or pig performance, but the improvement in ATTD of GE and N in pigs fed diets containing DDGS when IB was added does warrant further investigation.