Feed formulation strategies play a critical role in mitigating heat stress in transition dairy cows, as demonstrated by an August 2023 trial in the Czech Republic where the temperature-humidity index (THI) reached 82. During this period of severe heat, researchers evaluated the effects of a targeted nutritional approach including rumen-specific live yeast, antioxidants rich in enzyme superoxide dismutase (SOD), and organic selenium supplementation. While all cows experienced a drop in milk yield, those receiving the supplement showed significantly less severe declines. This research highlight how nutritional solutions can support resilience, particularly around calving during heat stress events.
Ruminant Technical Manager
Lallemand Animal Nutrition
On August 8, 2023, the temperature-humidity index (THI) in Tatenice, Czech Republic, reached 82 — well into the severe heat stress range for dairy cattle. For the next two weeks, this elevated THI would test every cow in the 500-head herd. While some cows suffered milk losses of nearly 7 kilograms per day, others maintained their production with losses of less than 4 kilograms daily. The difference wasn’t management, genetics or cooling systems; it was a targeted nutritional intervention based on understanding heat stress as a multi-system biological challenge.
THE HEAT STRESS CHALLENGE
Heat stress begins affecting lactating dairy cows at 21°C. What’s more is that production losses start at just 18°C. The THI combines both factors to reflect what animals actually experience — as humidity rises, even constant temperatures become more stressful because the body’s cooling mechanisms become less effective. Once THI values exceed 72, production losses become inevitable. Dairy operations face these conditions with increasing frequency, making heat stress management a €120 annual direct loss cost per cow in milking herds.1,2
These periods lead to reduced feed intake and more standing time, resulting in less milk and poorer-quality milk.3,4 Plus, there are long-term side effects of heat stress that aren’t revealed until years later, including diminished mammary gland tissue development and poor calf health in offspring of heat-stressed cows.5,6 The wide-ranging effects of heat stress on dairy cows indicate this challenge involves multiple systems within the animal.
Traditional approaches focus on environmental cooling such as fans, misters, shade structures. While these remain essential, researchers from Lallemand Animal Nutrition have begun questioning whether heat stress represents a single environmental problem or a cascade of biological disruptions requiring multiple intervention points. The Czech study emerged from this hypothesis: What if heat stress impacts could be addressed by simultaneously supporting the three major biological systems under stress?
A REAL-WORLD TRIAL
This study began in June 2023 with a comprehensive design on a commercial 500-cow herd dairy farm. Researchers evaluated the impact of a three-ingredient feed solution during the transition period under heat stress conditions in a randomly selected subgroup of 40 dairy cows.
The first ingredient targeted rumen efficiency with Saccharomyces cerevisiae CNCM I-1077, a rumen-specific live yeast strain. The second ingredient provided cellular protection through antioxidants rich in enzyme superoxide dismutase (SOD) at 50 milligrams daily. The third ingredient supported selenium levels through an inactivated yeast containing elevated levels of organic selenium at 1.2 milligrams per head daily, equivalent to 0.05 milligrams per kilogram of dry matter intake (DMI).
The key insight driving this approach was simultaneous rather than addressing heat stress as a single problem requiring a single solution, the intervention recognized that thermal challenges create cascading biological disruptions requiring coordinated support.
BIOLOGICAL CASCADE OF HEAT STRESS
The rumen is the centerpiece of the cascade of events that links heat stress to reduced performance and poorer health. As heat stress imbalances rumen microbiota, rumen function becomes impaired which may ultimately lead to acidosis. During hot periods, feed intake can also be disrupted by the heating of silage. Combined with other physiological stresses due to heat, animals face an increase in oxidative stress.
Stabilizing the Rumen Function
Rumen function becomes unstable. The complex microbial ecosystem responsible for fiber digestion operates within narrow pH ranges. Heat stress alters feeding patterns, reduces saliva production, and changes microbial populations, creating conditions favoring acidosis and reduced nutrient absorption.
Feeding Saccharomyces cerevisiae CNCM I-1077 works by interacting with the animal’s microbial population, bacteria, fungi, and protozoa, in the anaerobic rumen environment. This specific strain stimulates lactate-utilizing bacteria, promotes fiber colonization by cellulolytic bacteria and fungi, and increases fiber degradation with positive effects on milk production.
Supporting the Cellular Protection System
Cellular oxidative stress increases dramatically. Oxidative stress results from an imbalance between pro-oxidant and antioxidant molecules, causing an overproduction of reactive oxygen species (ROS) at the cellular level. This overproduction of ROS could overwhelm the animal’s normal antioxidant capacity and lead to a physiological imbalance, possibly causing cellular damage and altering animal health and performance. The antioxidant ingredient provides superoxide dismutase (SOD) from melon juice powder that directly support the body’s natural antioxidant production, while selenium-enriched yeast, a highly bioavailable source of organic selenium, serves as an essential cofactor for the body’s own antioxidant enzymes, enhancing the cellular defense system against oxidative stress.
Boosting the Immune Support Pathway
Heat stress alters immune cell activity, leaving animals more vulnerable to infections and metabolic disorders. These substances support the immune system to help maintain animal health and help modulate oxidative stress — which is increased during heat stress periods.
Selenium functions as a cofactor for glutathione peroxidase (GPx), one of the main antioxidant enzymes able to neutralize the negative effect of oxidizing compounds, limit the cellular oxidative stress induced by the reactive oxygen species, and to protect cells from damage. As a result, feed formulation strategies supporting the antioxidant defense can help maintain milk quality and cow fertility during challenging periods.
These systems interact synergistically. Improved rumen function enhances nutrient absorption, providing substrates for milk production. Reduced oxidative stress supports cell function. Enhanced antioxidant status helps maintain ruminant health. This biological integration explains why the multi-component approach proved more effective than single-target interventions.
WHEN THEORY MEETS REALITY
Results of the Czech Republic study showed the cows supplemented with a rumen-specific live yeast, melon juice powder rich in enzyme superoxide dismutase (SOD), and organic selenium reached peak lactation earlier than the control group. In addition, milk production exceeded 6.5 kg per head per day at its peak. From days zero to 100 in milk, production was higher by 1.7 kg per head per day on average in the supplemented group — a steady improvement suggesting enhanced efficiency rather than temporary production spikes.5 (Figure 1)
Then came the ultimate test. For 14 days in August, the barn experienced heat stress with a THI index up to 82 and remained elevated. During this time, milk production dramatically decreased for the control cows — dropping by 6.9 kg per day while the supplemented cows only experienced a drop of 3.8 kg per day. (Figure 2) In addition, the supplemented groups had lower somatic cell counts (SCC) and a lower number of artificial insemination attempts needed per positive pregnancy test.5
with rumen-specific live yeast, selenium-enriched yeast, and a superoxide dismutase (SOD) antioxidant.7
With three components added to the ration, the return-on-investment was greater than 9:1 considering the production and internventionssavings.5 Each feed ingredient appeared to help dairy cows guard against the main pathways harmed by heat stress: rumen function and oxidative stress — leading to a 45% reduction in heat stress impact among the supplemented group.
THE BIGGER PICTURE
As climate change intensifies environmental challenges and heat stress is poised to become an increasingly widespread concern — occurring during previously temperate seasons and climates. This trial on a commercial farm shows supplementation can be integrated with traditional cooling methods to provide additional support. Rather than seeking single solutions for multifaceted problems, this research embraced systems thinking — recognizing that heat stress disrupts multiple biological pathways requiring mitigation strategies.
Dairy herds should be prepared to meet production and profitability demands by moving to a system-wide approach, involving every aspect of the farm in battling heat stress to maintain productivity. Providing a nutritional approach helps cows become more resilient to heat stress events that have become increasingly unpredictable in recent years. Since heat waves can strike suddenly and without warning, producers should consider implementing these feed formulation strategies as a proactive management tool rather than waiting for extreme temperatures to arrive before making dietary adjustments.
The study also validates the importance of feed formulation strategies and commercial farm research conducted in real-world conditions. This farm environment represents the reality facing commercial producers worldwide.
References
1Kadzere, C. T., Murphy, M. R., Silanikove, N., & Maltz, E. (2002). Heat stress in lactating dairy cows: A review. Livestock Production Science, 77(1), 59–91. https://doi.org/10.1016/S0301-6226(01)00330-X
2St-Pierre, N. R., Cobanov, B., & Schnitkey, G. (2003). Economic Losses from Heat Stress by US Livestock Industries1. Journal of Dairy Science, 86, E52–E77. https://doi.org/10.3168/jds.S0022-0302(03)74040-5
3Ninomiya, S., Goto, Y., Huricha, Onishi, H., Kurachi, M., & Ito, A. (2023). Lying posture as a behavioural indicator of heat stress in dairy cows. Applied Animal Behaviour Science, 265, 105981. https://doi.org/10.1016/j.applanim.2023.105981
4Cook, N. B., Mentink, R. L., Bennett, T. B., & Burgi, K. (2007). The Effect of Heat Stress and Lameness on Time Budgets of Lactating Dairy Cows. Journal of Dairy Science, 90(4), 1674–1682. https://doi.org/10.3168/jds.2006-634
5Tao, S., Orellana, R. M., Weng, X., Marins, T. N., Dahl, G. E., & Bernard, J. K. (2018). Symposium review: The influences of heat stress on bovine mammary gland function1. Journal of Dairy Science, 101(6), 5642–5654. https://doi.org/10.3168/jds.2017-13727
6Skibiel, A. L., Dado-Senn, B., Fabris, T. F., Dahl, G. E., & Laporta, J. (2018). In utero exposure to thermal stress has long-term effects on mammary gland microstructure and function in dairy cattle. PLOS ONE, 13(10), e0206046. https://doi.org/10.1371/journal.pone.0206046
7Data on File at Lallemand Animal Nutrition. Czech Republic, 2023 Trial Data.
About Aurélien Piron
As the Ruminant Technical Manager of Lallemand Animal Nutrition, Aurélien Piron is responsible for technical support of the ruminant feed additives range, including deployment of on-farm services, training of field sales teams, collaboration on R&D programs and field projects with customers across the globe. Piron particularly focuses on precision nutrition for dairy cows and the integration of rumen-specific live yeast effects into nutritional software. Passionate about ruminant behavior, he also contributes to the development of services using large data analytics to better assess cow performance and welfare. He holds a Master of Science in Animal Production from the University of Angers (France).
