Researchers tested whether a special yeast supplement could help dairy cows fight a common udder infection caused by bacteria called Streptococcus uberis. They gave 42 healthy cows either the yeast supplement or a placebo for several months, then deliberately exposed them to the bacteria to see how well each group fought off the infection. While the yeast supplement didn’t prevent the infection or reduce overall milk problems, it did show a small benefit in cows that had a specific virus. The results suggest that while yeast supplements are generally safe, they may not be a strong defense against this particular type of udder infection.

The Quick Take

  • What they studied: Whether feeding dairy cows a yeast-based supplement could help them resist or recover faster from a common udder infection
  • Who participated: 42 healthy dairy cows of different ages (first-time mothers through fifth-time mothers) that had no recent udder infections and low bacteria counts in their milk
  • Key finding: The yeast supplement didn’t prevent the infection or help cows recover faster overall. However, in a small group of cows with a specific virus, the supplement did increase how much they ate and how much milk they produced
  • What it means for you: If you work with dairy cows, this yeast supplement appears safe but may not be worth the cost as a primary defense against this type of udder infection. The supplement might have some benefit for cows with certain health conditions, but more research is needed

The Research Details

This was a carefully controlled experiment where researchers randomly assigned 42 dairy cows to two groups: one received a yeast supplement mixed into their feed, while the other group received ground corn (a placebo that looked and felt similar). The study had three phases: a 45-day preparation period where researchers monitored the cows’ health, a challenge phase where they intentionally exposed one udder to the bacteria, and a 45-day recovery period. Researchers collected milk samples regularly to measure bacteria levels and white blood cell counts, which indicate infection.

The researchers used a technique called “blocking” to make sure both groups were as similar as possible at the start. They matched cows based on age, milk production, how long they’d been milking, and whether they had a specific virus. This careful matching helps ensure that any differences between groups were due to the supplement, not other factors.

The study used statistical methods designed for this type of experiment to analyze whether the supplement made a real difference. The researchers looked at multiple outcomes including how much the cows ate, how much milk they produced, and how quickly they recovered from the infection.

This research approach is important because it tests the supplement under controlled conditions where researchers know exactly what bacteria the cows are exposed to and in what amount. This is different from real-world farms where many different bacteria might be present. The careful study design helps prove whether the supplement actually works or if any benefits are just coincidence

This study has several strengths: it was a randomized controlled trial (the gold standard for testing treatments), it used a reasonable sample size, and it carefully controlled for factors that might affect results. However, the study used an artificial infection model rather than naturally occurring infections on farms, which means results might not perfectly match real-world situations. The study was also limited to one type of bacteria and one supplement product, so results may not apply to other infections or products

What the Results Show

The main finding was that the yeast supplement did not help cows fight off the udder infection in most cases. When researchers deliberately exposed the cows to the bacteria, both groups got sick at similar rates. The supplement-treated cows took about 4.84 days to show signs of infection compared to 3.88 days for the control group—a difference of less than one day that could easily be due to chance. Recovery time was similar in both groups, with supplement-treated cows taking about 22.5 days to clear the infection compared to 25.9 days for controls, but this small difference wasn’t statistically significant.

The supplement also didn’t affect how much milk the cows produced during any phase of the study, how much they ate, or the composition of their milk. These findings suggest that the yeast supplement was safe (it didn’t harm the cows) but didn’t provide the protective benefits researchers hoped to find.

Interestingly, when researchers looked at a smaller group of cows that had a specific virus (bovine leukemia virus), the results were different. In these cows, the supplement increased feed intake by about 1.3 kilograms per day and increased milk production by about 2.3 kilograms per day. This suggests the supplement might help cows with certain health conditions, though this finding needs confirmation in future studies.

The study tracked several other measures of health and production. Milk quality (measured by white blood cell counts) was similar between groups during all phases. The number of bacteria in the milk during the infection phase was also similar. Body weight changes and overall health indicators showed no meaningful differences between the supplement and control groups. The only notable secondary finding was the improved feed intake and milk production in the virus-infected subgroup, which was unexpected and warrants further investigation

Previous research had suggested that yeast supplements might reduce infection rates in dairy cows by boosting immune function. This study’s results don’t fully support that idea, at least for this specific type of udder infection. However, the finding that the supplement might help virus-infected cows is new and interesting, suggesting that yeast supplements might work better in cows with compromised immune systems. The study adds important information showing that supplements that seem promising in laboratory tests don’t always work as expected in real animals

The biggest limitation is that this study used an artificial infection model where researchers deliberately exposed cows to a specific amount of one type of bacteria. Real-world udder infections are messier—cows might be exposed to different bacteria, different amounts, and in different ways. The study also only tested one specific yeast product at one dose, so results might not apply to other yeast supplements or different amounts. The sample size of 42 cows is relatively small, which means the study might have missed real but small benefits. Finally, the interesting finding about virus-infected cows was based on only a subset of animals, so it needs to be confirmed in larger studies before drawing firm conclusions

The Bottom Line

Based on this research, the yeast supplement is not recommended as a primary strategy to prevent or treat this type of udder infection in most dairy cows. The supplement appears safe and may have some benefit for cows with certain viral infections, but the evidence is not strong enough to recommend it for general use. If you’re considering this supplement, discuss it with your veterinarian to determine if your specific herd might benefit. More research is needed before making firm recommendations

Dairy farmers and veterinarians should be aware of these results, especially those considering yeast supplements as part of their udder health program. This research is most relevant to farms dealing with Streptococcus uberis infections. The findings may be less relevant to farms primarily dealing with other types of udder infections. Cows with compromised immune systems (such as those with certain viral infections) might potentially benefit, but this needs further study

In this study, researchers observed cows for 95 days total (45 days before infection, 5-7 days during infection, and 45 days after). If the supplement were going to help, benefits would likely appear within this timeframe. However, since the supplement didn’t show clear benefits in the main group of cows, farmers shouldn’t expect to see dramatic improvements in udder health from this supplement alone

Want to Apply This Research?

  • Track daily milk production and somatic cell count (SCC) measurements weekly. Record any clinical mastitis cases with date of onset and recovery time. For cows receiving the supplement, note any changes in feed intake or milk quality compared to baseline
  • If using this supplement, implement it as part of a comprehensive udder health program that includes proper milking hygiene, regular monitoring, and veterinary care—not as a replacement for these practices. Monitor treated cows closely for any changes in health or production
  • Establish a baseline of udder health metrics (SCC, mastitis frequency, recovery time) before starting supplementation. Continue monitoring these same metrics monthly for at least 3-6 months to determine if the supplement provides any real benefit for your specific herd. Compare results to your historical data and to non-supplemented control cows

This research describes a controlled laboratory study using artificial infection in dairy cows. Results may not apply to naturally occurring infections on farms. The yeast supplement tested in this study did not prevent or significantly reduce infection in most cows. Before using any supplement for your dairy herd, consult with your veterinarian to discuss whether it’s appropriate for your specific situation. This summary is for informational purposes and should not replace professional veterinary advice. Always follow label directions and consult healthcare providers before making changes to animal nutrition or health management programs.