Can Yeast Replace In-Feed Antibiotics?

Project Title

Understanding the Modes of Action of Yeast as a Direct Fed Microbial for Feedlot Cattle


Katie Wood (University of Guelph) and Greg Penner (University of Saskatchewan)

Status Project Code
In progress. Results expected in December, 2022 ANH.01.21


Improving gut health and reducing liver abscesses, while maintaining performance is a major challenge. Direct fed microbials such as yeasts may improve gut health in ruminants. Dietary yeast and fermentation products may reduce the incidence and severity of acidosis in susceptible cattle. Feeding yeast may alter gut microbial profile and improve digestibility and gut health and may also improve immune response in cattle. The greatest incidence and severity of ruminal acidosis in feedlot cattle occurs late in the finishing period, but limited work has investigated using yeast to improve gut health at this time. The overall goal of the proposed studies is to understand the modes of action of yeast fed to finishing beef cattle and how they influence growth performance and gut health. These proposed modes of action include: total tract digestibility, rumen pH, gut barrier function, the impact on the microbiome, and gut immune response markers. Yeast is relatively inexpensive so may make a suitable replacement for antimicrobials like Tylan.

A publication from this group saw no difference in ADG but a 30% reduction in feed intake, 50% better F:G, 25% less variation in day-to-day feed intake, and tended to see better rumen pH compared to controls. However, this project used a “natural” production system (no monensin/implants); these findings need to be confirmed in a more conventional system. Yeast’s potential modes of action are also unknown.


  • Determine the impact of different forms of yeast (live active, heat killed, rumen protected) on steer performance and efficiency, rumen pH, total tract digestibility, gut health and economics.
  • Determine the impact of supplementing cattle fed a high grain diet with dry active yeast on in vivo gut barrier function, fecal starch, rumen pH and fermentation following an acidosis challenge and recovery.

What they will do

A metabolic trial in Saskatoon will feed 14 cattle (7 per treatment, based on earlier results) two barley-based finishing diets (33ppm monensin vs. 33ppm monensin plus 5g / 60 billion yeast cells). After a month of adaptation to the diet and 5 days of baseline measurements, intake will be restricted by 50%, then overfed to induce acidosis. They will measure rumen (pH, VFA, lactate), fecal (starch, VFA) and blood (immune markers) parameters during the challenge and recovery periods.

A feedlot trial in Guelph will feed 120 cattle one of five diets (24 head per treatment). The high moisture corn (88-90%) / haylage (10-12%) finishing diets will include (1) control (including monensin), (2) positive-control (tylan+monensin), (3) dry active yeast, (4) rumen protected yeast, and (5) heat killed yeast. Cattle will be fed from 960 to 1,600lbs. Over the last 100 days on feed they will measure ADG, F:G, feed (intake, behavior, and variability). Rumen pH will be continuously monitored on 10 head per treatment. Rumen and intestine health, VFAs, digestibility will be scored and collected on all animals at slaughter. Standard liver abscess and grading data will be collected and production economics will be evaluated.


This research will assess whether a commercially available yeast product is a viable alternative to in-feed antibiotics to maintain gut health in cattle fed high energy finishing diets.