Dr. Baumgard opens by explaining the origin of the “immune suppression” theory in transition cows. Research dating back to the late 1970s showed slower neutrophil infiltration into the mammary gland in early lactation, which led to the assumption that cows are immunosuppressed after calving. This idea has shaped industry thinking for more than 40 years. (10:43)

He outlines two primary mechanisms traditionally blamed for immune suppression: the cortisol surge at calving, which may impair neutrophil migration, and the metabolic changes of early lactation—high NEFAs, ketones, and low calcium—which appear to reduce neutrophil function in laboratory settings. (13:16)

Dr. Baumgard then challenges the central assumption: are cows truly immunosuppressed, or are they simply exposed to greater pathogen loads and stressors during a narrow window around calving? He argues that morbidity may reflect increased environmental and physiological challenges rather than a dysfunctional immune system. (15:25)

Dr. Fry shares field data from three herds representing over 100,000 calvings. After implementing management changes—primarily building a well-designed transition barn with lower stocking density, improved hygiene, and better cow flow—metritis rates dropped from 21.3% to 9.7%. Nutrition and innate immunity remained unchanged, suggesting management and environment were key drivers. (21:29)

The panel discusses the role of stress stacking during the transition period. Dr. Baumgard explains that multiple simultaneous stressors, such as overcrowding, heat stress, hygiene challenges, social stress, and nutritional shifts, may overwhelm cows. He emphasizes growing evidence that stress compromises gut integrity (“leaky gut”), potentially triggering systemic inflammation and increasing susceptibility in tissues like the mammary gland. (27:27)

Heat stress provides another example. While mastitis rates often increase during humid Midwest summers, they decline in arid regions like Arizona and Israel despite severe heat stress. Dr. Baumgard suggests environmental pathogen load—not immune suppression—is the primary driver. (27:43)

The conversation shifts to ketosis and hyperketonemia. Dr. Baumgard and Dr. Pralle discuss how elevated BHB and NEFAs may not always indicate disease but instead reflect normal metabolic adaptation to support milk production. The key distinction is productivity: cows milking well with high ketones may not require intervention, while cows with high ketones and poor milk production warrant deeper investigation into underlying causes such as metritis, mastitis, hypocalcemia, gut inflammation, or environmental stress. (37:13)

Dr. Fry reinforces the importance of whole-cow and whole-environment evaluation rather than treating metabolic markers in isolation. Monitoring milk yield, rumination, activity, and cow demeanor—along with assessing stocking density, pen hygiene, hoof health, and stockmanship—are critical to identifying true problems. (44:00)

The group emphasizes reducing pathogen load through simple, practical management: minimizing manure accumulation, maintaining clean and dry bedding, improving calving hygiene, and lowering stocking density—especially for close-up and fresh cows. (33:39)

Looking ahead, Dr. Baumgard describes his lab’s focus on modeling “stacked stressors” to better replicate the real-world transition period. Rather than studying stressors in isolation, his team is investigating how combined stressors influence physiology, particularly gut health. (47:11)

In closing, the panel encourages industry professionals to reconsider the immune suppression paradigm. Instead of trying to “fix” the immune system at calving, the emphasis should shift toward removing stressors and minimizing environmental challenges that create excessive pathogen exposure. (53:01)

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Dr. Penner presented “Progress in the gut: What we know about ‘gut health’” to lead off the symposium. He highlights using rumen acidosis as a model for gut health, focusing on key structures and how paracellular permeability is maintained or dysregulated, absorptive function, and microbiology. He notes that rumen acidosis affects other parts of the gut besides the rumen. (4:52)

Dr. Laarman wrapped up the symposium with “Gut health in ruminants: Where to from here?” He agrees with Dr. Penner that we need to look beyond the rumen at all other gut organs. His group has researched rumen acidosis in calves and how it’s linked to hindgut acidosis and pH dynamics. Calves behave very differently from cows in this model. Gut health begins from birth and is the whole tract, not just the rumen. (7:35)

Work in Dr. Penner’s lab showed that inducing inflammation in the mammary gland actually tightened permeability in the GI tract, which was opposite of their initial hypothesis. Dr. Baumgard’s lab found similar results in a heat stress model, and Dr. Laarman echoes that his group has also found this result. The panel discusses possible mechanisms of action. Dr. Penner explains that diet may also have an influence on gut permeability. (11:01)

The panel talks more about what we know and don’t know about gut health. We probably know which regions of the gut are most likely to be affected by challenges, what those impacts are, how fast those gut changes occur, and how nutrient absorption can be affected by challenges. The group hypothesizes that pH alone does not have a negative effect, but if low pH occurs at the same time as other signals or molecules, then pathology happens. Dr. Laarman shares some of the observations his group has made with calves, which withstand low pH that would kill a mature cow if she experienced it. (18:40)

Guests talk about some of the reasons why we know less about ruminant gut health compared to monogastric species. They also visit about the microbiome and how perhaps what the microbiome is doing and producing is more important than who all is present in the microbiome. (23:44)

Panelists share their take-home thoughts. (29:33)

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Recommendations for identification and selection of bioactive compounds to develop antimethanogenic feed additives. Dr. Yáñez-Ruiz (8:23)

How can we search for molecules that modify how feed is fermented in the rumen? Conventionally, we have used scientific literature to look for plant extracts and compounds that have been researched before. Now, we have computational technology that offers opportunities to model how molecules interact with rumen microbes. Once a candidate compound is selected, in vitro tools can be used to test dose responses before animal experiments.

Recommendations for testing enteric methane-mitigating feed additives in ruminant studies.

Dr. Yáñez-Ruiz for Dr. Alexander Hristov (17:07)

Once compounds have been identified and selected, they need to be tested in the animal. These experiments are costly and best practices for experimental design, animals used, diets fed, delivery of the test compound, and measurement of methane should be followed. Some of these guidelines are strongly linked to the regulatory aspects that provide requirements for how in vivo trials need to be conducted.

Feed additives for methane mitigation: Modeling the impact of feed additives on enteric methane emission of ruminants—Approaches and recommendations. Dr. Bannink (22:43)

Once experimental data is collected, it can be used to develop models to predict how effective an additive is, how it works, and its relevance. The intention is to quantify how an additive will work if you feed it to an animal. This can be complex due to variation among different datasets and natural fluctuation in methane production in the animal. One factor that plays a big role in the effectiveness of additives is the type of diet that animals are fed.

A guideline to uncover the mode of action of antimethanogenic feed additives for ruminants. Dr. Belanche (30:03)

Understanding the mechanism of action for methane mitigants is challenging. We know some compounds work to reduce methane, but we don’t know how or why they are working. There are five main types of additives when grouped by mode of action: modify rumen fermentation to decrease hydrogen production; methane inhibitors that act specifically against methanogens; inhibit enzymes common to all methanogens; hydrogen sinks to redirect hydrogen away from methanogenesis and toward other metabolic pathways; and promote methanotrophs that oxidize methane. The most effective are methane inhibitors, which decrease methane but don’t increase animal productivity. Combining a methane inhibitor with a hydrogen sink may help redirect hydrogen and result in improved animal productivity.

Regulations and evidence requirements for the authorization of enteric methane-mitigating feed additives. Dr. Tricarico (41:22)

There are as many regulatory systems as there are jurisdictions. Two concepts that are shared across jurisdictions are regulatory status/legal classification and intended use. While each jurisdiction requires some legal classification of a feed additive compound, each has a different criteria base from which they classify products. For example, “inhibitor” is a legal classification in New Zealand, but doesn’t even exist in other jurisdictions. Sometimes, the same word may mean different things in different jurisdictions. Authorization of a compound is not a blanket authorization, it is an authorization of the intended use of the compound. This specificity is critical for all involved to understand.

Feed additives for methane mitigation: How to account for the mitigating potential of antimethanogenic feed additives—Approaches and recommendations. Dr. del Prado (49:42)

A major challenge in this area is what kind of accounting system will be used: farm level, lifecycle analysis, carbon markets, national greenhouse gas inventories, etc. An accounting system needs to be well tailored from the type of experimental data available to the complexity used on the scale of the method. Experimental data, modeling, and accounting move hand-in-hand.

Panelists share their take-home thoughts. (58:57)

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