Leaky guts, brains, products, and profits

By Kevin J. Jacque, DVM, PAS

A producer called me around 6 am and noted he had lost a cow overnight. Seeing that this producer was an excellent client, I left my house earlier than normal before a dairy herd check to necropsy (think autopsy) his cow. We discovered several loops of middle intestine with hemorrhagic wall and contents. I noted the signs were consistent with hemorrhagic bowel syndrome, sometimes called jejunal hemorrhagic syndrome. The producer said, “What did I do wrong? What do I do now?” That led me into a common conversation I have had with clients about the inner workings of their animals’ intestines, the value of good feed, and the reliability of a consistent feeding and management protocol.

You are probably wondering why I would start an article in such a way. Here in lies the answer – the gut is not all what you have forethought. Enter the term “leaky gut.” Leaky gut is described in humans as a “consequence of impaired intestinal barrier function in chronic conditions” (Chae et al., 2024, DOI: 10.4014/jmb.2312.12031). In human nutrition, it is also referred to as a state of gut dysbiosis and imbalance. During gut dysbiosis, the gut microbial populations are imbalanced and lead to “disturbances of the dynamic interplay between the host and the microbiotia” (Marcari et al., 2025. DOI: 10.1007/s13668-025-00614-7). The dysbiosis basically means that your gut microbes are not in an ideal balance and that the imbalance leads to negative effects on gut function, the mucosal surface integrity, and the ability to fight off and defend against invading pathogens, toxins, or disease-states through the gut lining. Human nutrition has offered solutions to gut dysbiosis such as probiotics, juices, vegetables, “cleanses,” medications, and even bovine colostrum supplements.

That’s all nice and swell, but for farming operations, why do we care about dysbiosis and leaky gut syndrome? Leaky gut syndrome and gut dysbiosis are extremely common in animal species. A cow with a case of pneumonia will have temporary gut dysbiosis and leaky gut effects. A goat that has just arrived at the fair for the week in the middle of August will also experience dysbiosis. Your beloved Fido the dog at Thanksgiving, eating extra table scraps from the banquet meal, is at risk of dysbiosis and leaky gut secondary effects. Gut dysbiosis causes inflammation within the intestine that can then be felt in all areas of the body. The local effects of inflammation can then be transferred between organs and lead to greater issues. These are very common conditions, so let us dive into more practical considerations.

What does gut dysbiosis and leaky gut do to animals? The conditions can decrease production parameters like milk production, average daily gain, growth, maintenance of immune function, lower birth rate, lower fertility rate, increased dystocia, increased risk of conditions like ketosis, pregnancy toxemia, polioencephalomalacia, and more. The effects can be mild, such as an animal off-feed for a few hours to days, or they can be more moderate, like lower production and increased risk of disease. Animals can also have severe effects, such as death, abortion, or stillbirth.

How does gut dysbiosis happen? The most common cause of these issues is due to abrupt changes in the feed or nutrient intake of the animal. Some common examples would be inadvertent fasting or lack of feed for hours to days then abruptly back into dense nutrient feeds, changes in dry matter of silage due to weather, changes in feed microbial quality due to poor harvest and storage, abruptly changing types of milk or milk replacer without time for transition, abrupt weaning, animals getting into large volumes of grains or concentrates or undesirable feeds or plants. Animals that are already sick for other reasons (pneumonia, mastitis, metritis) will have highly variable feed intake and are at greater risk for issues to occur. Remember the cow autopsy from the beginning? That particular cow had actually been the first of several cows in the week that died from a major mistake in dry matter calculation and feed quality. The farm had not run a recent dry matter test during the wet rains, resulting in the loss of four cows that week alone.

You’re probably thinking by now, “That is a lot of words and nothing to show for it, Dr. Jacque.” You’re right. So, what can we do to prevent and treat gut dysbiosis? Here are some opportunities:

1. Limit abrupt changes in diet, whether it is the type of feeds or the quality of feeds.
2. Assay or test your stored feeds like silage and hay for quality, nutrient content, and microbial quality (high bacterial load, high Clostridium, etc.).
3. Avoid abrupt changes in young animals from whole milk/nursing to milk replacer. Change the diet slowly over five to seven days.
4. When disease challenges are high, feed prebiotics, probiotics, and postbiotics. (More on this to come in future articles).
5. Assist sick animals with supportive care like electrolytes, oral drenching or enteral nutrition, and injectable vitamins and minerals.
6. During periods of stress (weaning, castration, dehorning, pen-moves, vaccinating, implanting, tagging, etc.), offer consistent quality feeds.
7. For neonates, supplementing the milk or milk replacer with colostrum (small quantities) can assist in the gut lining’s defense against pathogens and scours (diarrhea).
8. Pre-condition animals to new diets or feeding arrangements before the expected event (think weaning or processing).

Perhaps this information is valuable to you, or I made it as clear as mud. For more in-depth information, consider discussing the topic with your veterinarian and nutritionist or an Extension consultant in your county. The more you can do to prevent gut dysbiosis, the more productive your herd, flock, or group of animals will be.