What’s in the Feed? Another Piece of the Animal Health Puzzle

By: Samanta Fensterseifer, DVM, MSc, Staff Research Scientist

Pathogens have a significant influence on animal health: the more pathogens are present, the higher the chances are of an animal displaying clinical disease symptoms. Coinfections like these are relatively common; our PathKinex™ surveillance across more than 4,000 cows and calves showed 61% of samples with simultaneous pathogen presence. Cows are resilient animals, but they can only handle so much. When external stressors such as water quality, overcrowding, transportation, weather events, and feed-related challenges compound with internal factors like pathogens, they create an effect far greater than any single issue could.

Because of this, it’s important to look at the whole puzzle. PathKinex™ analyses give us one portion, but there’s still a piece left to examine: the total mixed ration (TMR).

What TMR Hygiene Tells Us

When we talk about the TMR, we usually think about its nutritional profile: starch, fiber, protein, fat, minerals, and energy. But the TMR is also an ecosystem, containing bacteria, yeasts, molds, fermentation products, and, potentially, mycotoxins. The abundance of each component can change depending on the ingredients used, moisture, oxygen exposure, storage conditions, fermentation, time after mixing, and feed management practices.

To get a full understanding of TMR hygiene, we must examine several factors:

Mold: An Indicator of Fungal Growth

Molds are filamentous fungi that grow in favorable conditions of moisture, oxygen, temperature, and available nutrients. Growth often occurs during storage or feed-out, particularly when oxygen reaches previously protected silage. In dairy feeds, mold can be linked to nutrient losses and feed deterioration.

An elevated mold count could be a sign of fungal growth or feed deterioration, giving producers a reason to look more closely at silage storage, face management, feed handling, and other potential sources of contamination.

It is important to note that while mold often produces mycotoxins, the two may not always appear together. A mold count estimates the amount of viable mold present in a sample, but does not tell us whether those molds are producing mycotoxins. Likewise, mycotoxins can remain in feed even when viable mold is no longer detectable.

Yeast: A Driver of Feed Deterioration

Yeasts are naturally present in many fermented feeds, but, when certain yeasts are exposed to oxygen, they become active and consume lactic acid, one of the main acids responsible for preserving silage. This triggers a chain of events: Lactic acid consumption increases feed pH, which then provides the right environment for microbial growth. A host of negative effects can result from this growth, including heating, dry matter/energy loss, shifting fermentation characteristics, and decreased palatability and intake.

Yeast counts can therefore provide useful information about feed stability, particularly in silages and TMRs exposed to oxygen during storage, feed-out, mixing, or delivery.

Enterobacteria: A Sign of Microbial Contamination

Enterobacteria are a broad group of Gram-negative bacteria. While not all enterobacteria are pathogens, their presence in feed can nevertheless provide information about microbial contamination and preservation.

During ensiling, enterobacteria compete with lactic acid bacteria and contribute to protein degradation and the production of compounds such as ammonia and biogenic amines. Therefore, higher counts raise questions about fermentation, contamination, storage, or feed handling.

Mycotoxins: An Additional Chemical Challenge

Mycotoxins are secondary metabolites produced by certain fungi. Common mycotoxins found in cattle feed include aflatoxins, DON, fumonisins, T-2 toxin, zearalenone, and ochratoxin A. Different fungi produce different toxins, and more than one mycotoxin can be present in the same feed, creating another potential source of cumulative stress.

The rumen can transform or degrade some mycotoxins, but this protection varies based on the toxin type and rumen condition. Additionally, depending on the concentration, exposure duration, and animal, mycotoxins can affect feed intake, gastrointestinal and immune function, metabolism, reproduction, growth, and milk production.

How TMR and PathKinex™ Work Together

TMR hygiene analysis becomes particularly useful alongside pathogen surveillance. For our dairy PathKinex™ work, the TMR samples and rectal swabs are collected from the same pen. This gives us two different perspectives on the same production environment: The TMR provides information about potential exposure, while PathKinex™ sampling gives us a look at pathogens in the gastrointestinal tract that could potentially shed into the environment. The farm information and individual animal records provide the context needed to interpret both. These results can help identify patterns and determine where to look next.

Using this sampling method across multiple pens on each farm can also help determine whether a finding is isolated or more widespread. If one pen has an unusual TMR profile while other pens do not, the investigation can focus on factors specific to that diet or group of animals. 

When Stressors Stack Up

The importance of TMR hygiene becomes even clearer when we consider the many challenges an animal can experience at the same time. A cow may have to deal with:

• Pathogen pressure: E. coli, Clostridium, Salmonella, coccidia, fungi
• Feed-related challenges: Mycotoxins, mold, yeast, elevated bacterial counts
• Farm and environmental stressors: Heat, overcrowding, transportation, inconsistent feeding, reduced intake, water quality issues, weather changes

Each factor may be relatively small, but biological systems do not experience them independently. And this brings us back to the bigger idea: An animal’s ability to remain healthy depends on the balance between the challenges it encounters and its ability to respond to them.

Putting the Pieces Together

TMR hygiene is not a standalone diagnostic, and an elevated result does not automatically mean that animals will become sick—its value comes from putting that information into context. When multiple stressors and multiple pathogens are involved, there may not be one single answer. Sometimes, understanding the puzzle means knowing not just what the pieces are, but also how they fit together.

Works Consulted

Goeser, J. (2018, August 27). Troubleshooting feed hygiene challenges. Ag Proud. https://www.agproud.com/articles/21660-troubleshooting-feed-hygiene-challenges

Rock River Laboratory. (2017, January 13). Rock River Laboratory offers new diagnostics to combat feed challenges [Press release]. https://www.feedstuffs.com/market-news/rock-river-laboratory-offers-new-diagnostics-to-combat-feed-challenges

Rock River Laboratory. (n.d.). Anti-nutritional measures. https://rockriverlab.com/pages/Anti-Nutritional-Measures.php

Rock River Laboratory. (n.d.). Forage and TMR hygiene diagnostic. https://rockriverlab.com/file_open.php?id=254

Rock River Laboratory. (n.d.). Investigation of feed hygiene [Technical bulletin]. https://rockriverlab.com/file_open.php?id=298