Yeast doesn’t just make your bread rise… but also your profitability!


Source: Ministry of Agriculture, Food and Rural Affairs


Maintaining gut health is an important part of ensuring feedlot health, good animal performance, and efficient feed conversion. Metabolic disorders like ruminal acidosis and associated secondary disorders like liver abscesses and laminitis not only decrease feedlot performance, but also can impact carcass value and net economic returns. Research suggests that the period of highest risk of ruminal acidosis for feedlot cattle occurs in the second half of finishing period. In-feed antibiotics have historically been a method to improve these outcomes. However, new Canadian legislation effective December 1st, 2018 has resulted in changes to the access of antimicrobials used for controlling disease in animal production and improving feed efficiency, many of which are now under veterinary prescription. In addition, consumer preference for antibiotic-free products will continue to push research in the sector of alternative ‘natural’ feed additives. Direct-fed microbials like Saccharomyces cerevisiae (yeast) have been extensively studied as a natural feed additive and have shown promise as an antibiotic alternative to reduce risks of animal health disorders, such as ruminal acidosis in dairy cattle. The effectiveness of direct-fed microbials at an increased dose rate to reduce digestive upsets and improve animal health is not well established for beef feedlot cattle.

The Experiment

This experiment aimed to assess the effectiveness of yeast fed at double dose in the late finishing phase on cattle performance and to assess rumen pH, gut health, and carcass characteristics. The yeast in this study is a live active dry Saccharomyces cerevisiae product developed for use in cattle, pig, horse, sheep, and goat feed (Vistacell, AB Vista, Marlborough, UK). The original recommended dose of this product for feedlot cattle is 1.5 grams per head per day which was established based on research in dairy cattle. For this study, 3 grams per head per day of the product was added to the fed ration providing a high dose with a minimum of 60 billion colony forming units (CFU). Fifty-four steers were split up into 3 pens depending on weight and were randomly assigned to control (CON) groups, which were fed the finishing diet (60% high moisture corn, 20% dried distillers’ grains with solubles, and 17% alfalfa haylage), or the yeast (YST) group, which had the same diet with the yeast added.


Every 28 days, each steer was weighed, blood sampled, and ultra-sounded for backfat and rib fat thickness. Additional body weights and blood samples were collected three to five days before slaughter. Feed intake and feeding behaviour were recorded for each animal using individual RFID tags that corresponded to the assigned Insentec feeder (Insentec B.V., Marknesse, The Netherlands) that recorded each feeding event. Rumen pH was measured using ruminal data loggers, which were set up to record pH every five minutes for three weeks.

Reticulo-ruminal pH probe

Figure 1. Reticulo-ruminal pH probe.

Hot carcass weight, grade fat, ribeye area, liver and kidney weights, and liver abscess scores were measured and recorded at the time of slaughter. Afterwards, the entire digestive tract was dissected and rumen samples collected. The rumen was separated, emptied, and lightly rinsed with water and dissected as seen in Figure 1. Once dissected, a specimen of the rumen wall was obtained from the caudoventral sac for histology analysis. The rumen wall was then photographed, and health scored on a scale of 1 to 5 as seen in Figure 2. This scoring system focused on the visual appearance of the rumen papillae, specifically regarding coloration. Healthy papillae are free from pink or light grey to white discoloration and are uniform in colour and physical appearance.

Rumen dissection technique and papillae sampling location. Red dotted line is place of incision for dissection.

Figure 2. Rumen dissection technique and papillae sampling location. Red dotted line is place of incision for dissection.

Rumen health scores 1 (left), 3 (middle), and 5 (right).

Figure 3. Rumen health scores 1 (left), 3 (middle), and 5 (right).

Six to ten papillae removed from the rumen wall were fixed and stained for viewing on a microscope. The outer skin of the rumen papillae is made up of strata layers, responsible for absorbing nutrients while keeping unsafe molecules out of the system. Measurements of each strata layer; corneum, granulosum, spinosum, and basale (seen in Figure 3) were completed for each animal. Sloughing of the outer most layer, the corneum, was scored on a scale of 1 to 5.

Rumen papillae strata layers.

Figure 4. Rumen papillae strata layers.

Image taken at 40X magnification, black line represents 25 µm.


Performance results seen in Figure 4 show a 31% decrease in dry matter intake (DMI) for yeast-fed steers, while average daily gain (ADG) and ultrasound measurements were the same between treatment groups. This translated into improved feed conversion ratios (FCR) for the yeast-fed steers in comparison to the control steers. Additionally, the individual variation in DMI was less in yeast-fed steers than control steers. This suggests that yeast can reduce daily variation in feed intake, which may help reduce the risk of subacute ruminal acidosis in feedlot cattle.

Performance of control and yeast treated steers.

Figure 5. Performance of control and yeast treated steers.

Different letters indicate significant differences between groups.

There were significantly fewer visits to the feeder per day and smaller meal sizes for the yeast-fed steers when compared to the control steers (seen in Table 1). All other feeding behaviour parameters remained the same between treatment groups. No differences were found between the control and yeast-treated steers for rumen pH measurements, carcass traits or rumen papillae strata thickness.

Table 1. Feeding behaviour measurements of control and yeast treated steers.

Dietary Treatment
CON (n=27)
YST (n=24)
Time at feeder, min/d
Visits to feeder, visits/d
Time per visit, min/visit
Visit size, g DM/visit
Number of meals, meals/d
Time per meal, min/meal
Meal sizez, g DM/meal
Eating rate, g DM/min

zMeal is defined as any eating period with breaks no longer than 7 minutes

Different letters indicate significant differences between groups

Steer 128E using Insentec feeder.

Figure 6. Steer 128E using Insentec feeder.

Conclusions & Implications

The results of this experiment suggest that added yeast (60B CFU) to the diet in the later finishing period significantly decreased DMI and improved feed efficiency, while having no impact on carcass traits or average daily gain. Although added yeast reduced feed intake variability, there were no statistically significant improvements in rumen pH or rumen health scores. The ability of added yeast to improve feed efficiency while maintaining gains has excellent potential to reduce feed costs to producers without loss in productivity. Given the cost-effectiveness of yeast and the observed improvement in animal efficiency, the addition of yeast to feedlot diets three months before slaughter has the potential to improve feedlot operators’ bottom line.


The authors gratefully acknowledge the financial support from AB Vista, Ontario Ministry of Agriculture, Food, and Rural Affairs, K. Wood start-up funds, and the Department of Animal Biosciences.

Author: Melissa Williams, PhD Student – Department of Animal Biosciences, University of Guelp


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