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Stimulation of microbial protein synthesis by branched-chain volatile fatty acids in dual-flow cultures varying in forage and PUFA concentrations.

K. E. Mitchell

Abstract:

M23
Stimulation of microbial protein synthesis by branched-chain volatile fatty acids in dual-flow cultures varying in forage and PUFA concentrations.
K. E. Mitchell*1, B. A. Wenner1, C. Lee1, M. T. Socha2, J. L. Firkins1. 1The Ohio State University Columbus, OH, 2Zinpro Corporation Eden Prairie, MN.

Branched-chain amino acids (BCAA) are deaminated by amylolytics to branched-chain VFA (BCVFA), which are growth factors for cellulolytic bacteria that cannot degrade or synthesize their own BCAA. Our objective was to determine the dietary conditions that would increase the uptake of BCVFA. Increasing forage would increase cellulolytic bacterial abundance and their stimulation by BCVFA as growth factors. However, in a low forage diet, amylolytic bacteria should outcompete for BCVFA. Supplemental PUFA should inhibit cellulolytic bacteria growth, but additional BCVFA should minimize that inhibition. Supplementation of BCVFA could therefore increase efficiency of microbial protein synthesis in both low forage (LF), high forage (HF), and high PUFA diets. The study was an incomplete block design with 8 dual-flow continuous cultures used in 4 periods with treatments (n = 4) arranged as a 2 � 2 � 2 factorial. The factors were: HF or LF (67 or 33%), without or with supplemental corn oil (CO, 3% DM), and without or with 2.15 mmol/d each of isovalerate, isobutyrate, and 2-methylbutyrate (MB). The isonitrogenous diets consisted of 33:67 alfalfa: orchard grass pellet, and was replaced with ground corn and soybean meal in the LF diet. Data were analyzed with PROC MIXED in SAS (v. 9.4, SAS Institute 2015) with random effects of period and fermenter and fixed effects of diet, CO, BCVFA, and their interactions. The main effect of supplementing BCVFA increased (P = 0.10) NDF digestibility (NDFd) by 2.97% units, and CO increased (P = 0.07, for interaction) NDFd by 6.46% units in LF diets. BCVFA and HF increased (P < 0.03) bacterial N by 1.54 and 1.84 g/kg OM truly degraded, respectively. Total BCVFA net production was lower (P < 0.01) with HF compared with LF. When CO and BCVFA were supplemented with LF, total BCVFA net production decreased (P = 0.10, for interaction). When BCVFA was supplemented with CO, MB net production decreased (P = 0.08, for interaction) with HF, but even more with LF. Providing supplemental BCVFA improved efficiency of cellular growth of cellulolytics and therefore NDFd, which should improve feed efficiency in dairy cows.

Keywords: branched-chain VFA, cellulolytic, PUFA.

Biography: Kelly Mitchell is originally from Tulare, CA where she grew up around dairy cattle by following her father, Ken Mitchell a dairy veterinarian. After completing her undergraduate degree in Animal Sciences at UCD in 2015 she continued her education at UCD with Dr. Heidi Rossow and earned a MS in Animal Biology in 2017. Currently she is working towards her PhD with Dr. Jeff Firkins in The Ohio State University Nutrition program, while she also works as a research associate in the Animal Sciences Department.