About

Marshall Stern is a Professor Emeritus in the Department of Animal Science at the University of Minnesota Twin Cities. His research emphasizes protein nutrition of ruminants, including methodology for measuring protein degradation and microbial protein synthesis in the rumen, as well as protein absorption from the small intestine. He studies various factors affecting microbial fermentation and the rumen microbiome using continuous culture techniques. His teaching includes undergraduate courses such as Companion Animal Nutrition and Care, Animal Nutrition, and Ruminant Nutrition. Dr. Stern's extensive publication record includes research on microbial fermentation, rumen microbiome, and protein metabolism in ruminants, contributing significantly to the understanding of ruminant nutrition and digestion.

Research topics

• Food science
• Chemistry
• Biology
• Animal science
• Biochemistry

Selected publications

• Evaluation of iso-α-acid and β-acid extracts from hops (Humulus lupulus L.) on fermentation by rumen microbes in dual-flow continuous culture fermenters

  Animal Feed Science and Technology · 2019-12-23 · 5 citations

  articleOpen accessSenior authorCorresponding

  Hops (Humulus lupulus L.), primarily used in the brewing industry, have been shown to have bacteriostatic properties against Gram-positive bacteria. Active antimicrobial compounds contained within hop flowers include iso-α-acids (isohumulones) and β-acids (lupulones). Previous experiments have demonstrated effects of hop extracts on rumen fermentation in batch culture. The objective of this study was to determine the direct effects of iso-α-acids and β-acids on rumen fermentation in continuous culture fermenters. Two experiments were conducted using dual-flow continuous culture fermenters. Each experiment utilized eight fermenters in two consecutive 10 d periods. Within both experiments, the same basal diet consisting of 44 % corn silage, 14 % alfalfa hay, 13 % ground corn, 11 % protein mix, 10 % corn gluten feed, 5 % cottonseed and 3 % liquid vitamin and mineral supplements on a DM basis was provided to the fermenters at a rate of 75 g of DM/L of fermenter volume/day. In experiment 1, hop beta-extract was added daily to the artificial saliva buffer to supply 0 (CON), 600 (LOW), 1200 (MED), or 1800 (HIGH) mg of β-acids/kg of diet DM/day. In experiment 2, hop iso-α extract was provided to fermenters via the artificial saliva buffer to supply 0 (CON), 600 (LOW), 1200 (MED), or 1800 (HIGH) mg of iso-α-acids/kg of diet DM/day. Data in both experiments were analyzed as a randomized complete block design with experimental period serving as a block and all treatments equally represented within each block. Data were statistically analyzed using GLM procedure of SAS with a model including the fixed effects of experimental period (block), treatment, and the interaction of treatment and period. In experiment 1, mean and maximum fermentation pH increased (P = 0.005) linearly with increasing levels of beta extract inclusion. Additionally, time spent below pH 5.8 increased and time between pH 5.8 and 6.2 decreased (P = 0.007) linearly with greater beta extract inclusion (P = 0.08). However, beta extract did not affect DM, OM, NDF or ADF digestion. Furthermore, beta extract did not modify VFA production or N metabolism. In experiment 2, iso-alpha extract also increased average pH, and tended to increase time above pH 6.2. Iso-α extract did not affect DM, OM, NDF and ADF digestion, VFA production, or N metabolism. Results indicate that increasing the concentration of beta extract or iso-α extract increase rumen pH within continuous culture, but neither extract affects rumen nutrient digestion.

  PublisherDOI

• 390 Effects of dietary-induced pH changes on feed digestion, nitrogen metabolism, fermentation, and biohydrogenation of polyunsaturated fatty acids in dual-flow continuous culture fermenters

  Journal of Animal Science · 2019-12-01

  articleOpen accessSenior author

  Abstract Ruminal pH decreases as greater concentrations of grain are consumed, and as a result, reduces biohydrogenation of polyunsaturated fatty-acids. Our objective was to investigate effects of diet on pH and biohydrogenation activity in vitro. Eight dual-flow, continuous culture fermenters were blocked by side of the room and randomly assigned, within block, to 1 of 4 treatments. Treatments consisted of 100:0 roughage-to-concentrate (Grass), 50:50 roughage-to-concentrate plus flax oil supplement (Mix+F), 10:90 roughage-to-concentrate plus corn oil supplement (Con+C), or 10:90 roughage-to-concentrate plus flax oil supplement (Con+F). Fermenter pH, area under the curve, and maximum pH were lowest for Con+C and Con+F (P < 0.05). Apparent and true DM, OM, and NDF digestibility were greater with grain inclusion (P < 0.05) while ADF digestibility was not affected by treatment (P > 0.10). Protein degradation was lowered as grain inclusion increased (P < 0.05). Total VFA concentrations were lowest for Grass, highest for Con+C and Con+F, and intermediate for Mix+F (P < 0.05). Acetate-to-propionate was lowest for Con treatments (P < 0.05). Biohydrogenation of 18:2n-6 and 18:3n-3 fatty-acids were reduced (P < 0.01) with inclusion of concentrate regardless of roughage-to-concentrate ratio. Concentrations of stearic acid recovered from effluent were greatest for Grass, intermediate for Mix+F, and lowest for both Con+C and Con+F (P < 0.05). Linoleic acid proportions in effluent were greatest for Con+C and Con+F and intermediate for Mix+F (P < 0.05), and inclusion of concentrate, regardless of amount, increased the amount linoleic acid recovered from fermenter overflow (P < 0.01). Between Con+C and Con+F concentrations of alpha-linolenic acid (ALA) was greater when flax oil was supplemented (P < 0.01). Proportions of ALA in effluent was similar (P > 0.10) between Grass and Con+C; however, between Mix+F and Con+F ALA concentrations tended (P = 0.06) to be greater for Con+F. Omega6-to-omega3 ratios were similar across Grass, Mix+F, and Con+F (P > 0.10) and greatest for Con+C (P < 0.05).

  PublisherOA PDFDOI

• In vitro utilizable crude protein at the duodenum of dairy cows of various ecotypes of kochia scoparia fertilized with nitrogen

  Iranian journal of applied animal science · 2019-09-01

  articleOpen accessSenior author

  The aim of this study was to determine possible differences between first cut and second cut forage of Birjand ecotype of Kochia scoparia for chemical composition and fermentability, and to evaluate the changes may be induced by N fertilization in chemical composition, fermentability, and utilizable crude protein (uCP) supply at the duodenum of dairy cows of Sabzevar ecotype of Kochia. Birjand ecotype was sampled in mid bloom and Sabzevar ecotype was sampled in first bloom stage of maturity. Different in vitro gas production methods were used to determine gas production kinetics and uCP and effective uCP (EuCP) supply of the forage samples. Results of the first experiment showed that there is no significant difference between first cut and second cut forage of Kochia scoparia for gas production kinetics (P>0.05), but significantly lower content (g/kg DM basis) of neutral detergent fiber (NDF) (451.1) and hemicellulose (233.7) and higher content of CP (100.1) and ash (133.4) were observed in the first cut than those of the second cut plants (P<0.01). The results of second experiment indicated that the application of moderate levels of the N fertilizer (115 kg N/hectare) on Sabzevar stands of Kochia scoparia induced considerable changes in chemical composition, fermentability, and protein degradability of forge, so that, dry matter (DM), NDF, and hemicellulose declined and CP and ash content of forage increased (P<0.05). Moreover, the gas production kinetics decreased and supplied amounts of uCP and EuCP increased in association with increase in CP and true protein content (P<0.05).

  Publisher

• Comparisons of bacterial and archaeal communities in the rumen and a dual-flow continuous culture fermentation system using amplicon sequencing

  Journal of Animal Science · 2018-02-24 · 21 citations

  articleOpen accessSenior authorCorresponding

  Dual-flow continuous culture (CC) fermenters are commonly used to study rumen fermentation in vitro. Research using culture-based and oligonucleotide techniques has shown that certain microbial populations within fermenters may be maintained at abundances similar to those observed in vivo. In this study, bacterial and archaeal communities in the rumen of dairy cattle and in a dual-flow CC fermentation system were compared using high-throughput amplicon sequencing targeting the V4 hypervariable region of 16S rRNA. We hypothesized that the in vitro system harbored a comparable bacterial and archaeal community to that observed in the rumen. Members of the Bacteroidetes and Firmicutes made up the 2 most abundant phyla in the rumen, inoculum, and fermenters and did not differ among sample types (P > 0.10). Similarly, Prevotellaceae, the most abundant family in all 3 sample types, did not differ based on source (P = 0.80). However, beta diversity analyses revealed that bacterial and archaeal communities differed between fermenters and rumen samples (P ≤ 0.001), but fermenter bacterial and archaeal communities stabilized by day 4 of each period. While the overall bacterial and archaeal community differs between natural rumens and those detected in in vitro fermenter systems, several prominent taxa were maintained at similar relative abundances suggesting that fermenters may provide a suitable environment in which to study shifts among the predominant members of the microbial community.

  PublisherOA PDFDOI

• Comparison of warm season and cool season forages for dairy grazing systems in continuous culture1

  Translational Animal Science · 2018-04-01 · 8 citations

  articleOpen accessSenior author

  Abstract The objective of this study was to compare warm-season annual grasses to cool-season perennial (CSP) grasses for ruminal nutrient digestibility and N metabolism in a dual-flow continuous culture fermentation system. Dietary treatments were 1) fresh alfalfa, 2) CSP grasses and legumes, 3) brown-midrib sorghum-sudangrass (BMRSS), and 4) teff grass from an organic dairy production system. Eight dual-flow continuous culture fermenters were used during two consecutive 10-d periods consisting of 7 d for stabilization followed by 3 d of sampling. Fermenter samples were collected on days 8, 9, and 10 for analysis of pH, NH3-N, and VFA. Apparent DM, OM, NDF, and ADF digestibility were on average lesser (P &amp;lt; 0.05) in CSP grasses and legumes and warm-season annual grasses compared with alfalfa. True DM and OM digestibility were lesser (P &amp;lt; 0.05) for CSP grasses and legumes and warm-season annual grasses compared with fresh alfalfa. Total VFA were not affected (P &amp;gt; 0.05) by forage. The NH3-N concentrations were highest (P &amp;lt; 0.05) with alfalfa compared with the other CSP grasses and legumes and warm-season annual grasses. CP digestibility was not affected (P &amp;gt; 0.05) by forage treatment. Flow of NH3-N was greatest (P &amp;lt; 0.05) for alfalfa, reflecting the greatest NH3-N concentration. Flow of total N was greatest (P &amp;lt; 0.05) for alfalfa, intermediate for teff, and lowest for CSP grasses and legumes and BMRSS. Flows of bacterial N, efficiency of bacterial N, non-NH3-N, and dietary N were not affected (P &amp;gt; 0.05) by forage source. Overall, fermentation of warm-season grasses was similar to the cool-season grasses and legumes which indicate dairy producers may use warm-season grasses without concerns about negative impact on rumen health.

  PublisherOA PDFDOI

• Effect of dried fermentation biomass on microbial fermentation in continuous culture and in vitro intestinal digestibility

  Animal Feed Science and Technology · 2017-05-29 · 2 citations

  articleSenior authorCorresponding
  PublisherDOI

• Differences in in vitro hydrolysis and fermentation among and within high-fiber ingredients using a modified three-step procedure in growing pigs1,2

  Journal of Animal Science · 2017-11-30 · 16 citations

  articleOpen access

  In vitro DM disappearance (IVDMD) and gas production can be used to rapidly estimate apparent total tract digestibility of DM and GE in feed ingredients used in swine diets. However, the accuracy of the system in estimating ME among sources feed ingredients with high content of dietary fiber is not clear. Objectives of this study were 1) to measure IVDMD of feed ingredients with high insoluble fiber content and determine and compare in vitro gas production kinetics from fiber fermentation among wheat straw (WS; 16 sources; 69.0-83.4% NDF), soybean hulls (SBH; 16 sources; 60.9-67.7% NDF), and corn distiller's dried grains with solubles (DDGS; 16 sources; 28.8-44.0% NDF); and 2) to estimate ME contributions resulting from gas production of DDGS. Each 2-g sample was hydrolyzed for 2 h with pepsin and for a subsequent 4 h with pancreatin. Hydrolyzed residues were filtered, washed, dried, weighed, pooled within the same sample, and used for subsequent fermentation using swine fecal inocula. Volume of gas produced was recorded at 11 time points during 72 h of incubation. Parameters of gas production kinetics were calculated using a nonlinear monophasic model, and differences among ingredients were compared using a mixed model. The IVDMD from simulated gastric and small intestinal hydrolysis (IVDMDh) in DDGS (55.7%) was greater (P < 0.05) than that in SBH (19.7%), which was greater (P < 0.05) than that in WS (14.5%). In vitro DM digestibility from simulated large intestine fermentation (IVDMDf) of SBH (68.5%) was greater (P < 0.05) than that of DDGS (52.7%), which was greater than that of WS (41.8%). In vitro DM digestibility from simulated total tract digestion (IVDMDt) was greatest (P < 0.01) in DDGS (79.2%) followed by SBH (74.8%), and both were greater than that in WS (50.2%). The asymptotic gas production (mL/g substrate) was greater (P < 0.05) for SBH (293) than for DDGS (208) and WS (53). There were differences (P < 0.01) in IVDMDh among sources of WS, SBH, and DDGS, whereas IVDMDf and IVDMDt were different (P < 0.01) among sources of SBH but not among sources of DDGS or WS. There were no differences in asymptotic gas production among sources of WS, SBH, or DDGS. In conclusion, the modified 3-step procedure allowed for characterizing the variability of DM digestibility and asymptotic gas production resulting from residue fermentation among WS, SBH, and DDGS and among sources of each ingredient.

  PublisherOA PDFDOI

• Effects of bismuth subsalicylate and dietary sulfur level on fermentation by ruminal microbes in continuous culture

  Translational Animal Science · 2017-12-01 · 3 citations

  articleOpen accessSenior authorCorresponding

  Abstract In ruminants, excess dietary sulfur can be associated with a reduction in DM intake, poor feedlot performance and sulfur-associated polioencephalomalacia. Bismuth subsalicylate (BSS) has been shown to decrease hydrogen sulfide in vitro. The objective of this experiment was to evaluate effects of BSS inclusion (0 or 0.5% of diet DM) and dietary sulfur (0.21 or 0.42% of diet DM) on microbial fermentation in continuous culture. Treatments were arranged in a 2 × 2 factorial design. Eight dual-flow continuous culture fermenters were used during 2 consecutive 10-d periods consisting of 7 d for stabilization followed by 3 d of sampling. A pelleted feedlot diet containing 39% dry rolled corn, 32% earlage, 21% wet distillers grains, 3.2% corn silage, 1.5% soybean meal, 0.6% urea and 2.7% mineral premix (DM basis) was provided as substrate for microbes at a rate of 75 g of DM × fermenter–1 × d–1. Effluents from sampling days were composited by fermenter within period, resulting in 4 replicates/treatment. Bismuth subsalicylate inclusion decreased (P &amp;lt; 0.01) true OM digestion, while no effects were observed for NDF and ADF digestion. Total VFA concentrations, molar proportions of acetic, propionic, and branched-chained VFA decreased (P &amp;lt; 0.01) with BSS addition. The ratio of acetic to propionic acid and the molar proportion of butyric acid increased (P &amp;lt; 0.01) with BSS addition. In regard to nitrogen metabolism, BSS increased NH3–N concentration, NH3–N and dietary-N flows (P &amp;lt; 0.01), and decreased non-NH3–N flow, microbial-N flow, CP degradation, and efficiency of microbial protein synthesis (P &amp;lt; 0.01). Inclusion of BSS increased mean, minimum, and maximum fermentation pH (P &amp;lt; 0.01). Amount of dietary sulfur and BSS inclusion influenced flows of amino acids and fatty acids from fermenters. Influences on fatty acid biohydrogenation and amino acid flows demonstrated an overall suppression of microbial fermentation. Results from this experiment indicate that BSS inclusion at 0.5% of diet DM has detrimental effects on in vitro rumen fermentation in continuous culture.

  PublisherOA PDFDOI

• Comparison of undergraduate student learning gains and satisfaction when enrolled in animal science courses offered in person and online

  Journal of Equine Veterinary Science · 2017-05-01

  article
  PublisherDOI

• Undergraduate Student Learning Gains and Satisfaction in Online and In-Person Animal Science Courses

  Natural sciences education · 2017-09-07 · 3 citations

  article

  Core Ideas Student learning gains occurred using in-person and online methods. Student satisfaction was high for in-person and online methods. Online courses can be used to teach undergraduate students animal science courses. The number of colleges offering online courses is increasing. A survey showed 31% of students take at least one online course during college. However, limited data exists on learning gains and satisfaction from online animal science courses. The objective was to evaluate learning gains and satisfaction with animal science courses offered in-person and online at the University of Minnesota (UMN). Both courses offered in-person and online sections for two academic years. Researchers collected data from two introductory-level courses, Companion Animal Nutrition and Care and Horse Management, to assess learning gains and satisfaction of the two delivery methods. Learning gains were assessed by comparing pre- and post-tests. Satisfaction was evaluated through questions administered through the UMN's Student Rating of Teaching. Learning gains (12–41%) occurred in both courses and delivery methods, with in-person students having greater gains in three of the four course years (P ≤ 0.01). Satisfaction was high among both courses and delivery methods (≥4.8 on 6.0 scale), although in-person students reported higher ratings compared with online students in some instances (P ≤ 0.01). When evaluating undergraduate, introductory-level online and in-person courses, students utilizing both delivery methods experienced learning gains and were satisfied. Based on these results, online courses can be successfully used to teach undergraduate students introductory-level animal science courses.

  PublisherDOI

Frequent coauthors

• J.L. Firkins

  The Ohio State University

  51 shared

• D.L. Palmquist

  The Ohio State University

  49 shared

• John Huber

  Natural Resources Canada

  49 shared

• J.H. Clark

  Urbana University

  49 shared

• G.A. Varga

  49 shared

• J.G. Linn

  Optimal Solutions (United States)

  26 shared

• S. Calsamiglia

  Universitat Autònoma de Barcelona

  26 shared

• D.E. Otterby

  25 shared

Labs

• Department of Animal SciencePI

Education

• Ph. D., Animal Science

  University of Maine

  1978