ISSUE FOCUS FEED & ADDITIVE MAGAZINE July 2025 27 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 pro-
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