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Don’t Lose Another Cow to Hemorrhagic Bowel Syndrome

Karen Bohnert


June 21, 2021



An emerging, highly fatal intestinal disease of adult cows, Hemorrhagic Bowel Syndrome (HBS), draws concerns from dairy producers, veterinarians and nutritionists, as it is also known as the sudden death disease of dairy cattle.

According to Dr. Angie Rowson, a board-certified dairy practice veterinarian who has been working with HBS for nearly two decades, there is still not much known about HBS. She says that producers have either never heard of this disease, have sporadically seen HBS on their farm, or are constantly battling the disease.

HBS is characterized as an acute and sometimes massive hemorrhage in the small intestine, which can subsequently lead to the formation of intraluminal blood clots and obstruction. Furthermore, affected cows suffer from the collective effects of blood loss, intestinal obstruction and necrosis of the bowel.

As a veterinarian, Rowson’s boots on the ground work in central California allowed her to see firsthand the impact of this fatal disease in dairies, as she performed several HBS necropsies in dairy cattle. “One herd I worked with was losing eight to 10 cows a month from HBS,” Rowson says. “We wanted to get to the root of why this was happening. Not just because of the financial loss, but also because of the pain associated with the disease.”

Despite being a fatal disease, little attention regarding funding and research has been conducted. Many details surrounding HBS, including contributing factors, continue to be a mystery. “It is frustrating that no one in the U.S. is doing any new research on HBS,” Rowson adds. “The problem is we cannot recreate it in a lab, so we don’t know exactly what causes HBS. We only know bits and pieces and that the cause is multifactorial.”

Dr. Scott Bascom, technical services manager for Phibro Animal Health, agrees that much is unknown about what causes some cows to develop HBS and not others. “HBS cases are most common following stressful periods in a cow’s lactation cycle such as calving and early lactation, when cows are subject to several different stressors. These stressors can reduce immune function,” Bascom says. “The cow's immune system plays a role in whether a cow becomes an HBS cow. If the cow’s immune system becomes compromised the cow is more susceptible to the effects of invasive molds, toxins and pathogenic intestinal flora which can lead to HBS.” Common Denominator Any dairy breed can be associated with HBS, though Brown Swiss have been reported to be more predisposed. While HBS is reported to be sporadic, some dairies will have multiple cases within a few days. Other common denominators of cows with HBS are:

  • Second lactation or greater (although cases of younger lactation cows have had HBS).

  • Under 100 DIM (However, cows are usually between 100 and120 DIM when diagnosed with HBS.).

  • Producing larger volumes of milk and consuming larger volumes of feed.

  • Immunosuppressed.

  • Larger, higher production herds.

Rowson states that often cows who are higher in production levels consume a large volume of feed, and the diet at that stage of lactation is often high in protein and energy but lower in fiber. She also notes that feed is passing through the intestine at a faster rate. However, little research has been conducted to determine what impact this has on developing HBS. “Research from University of California-Davis shows that the bleeding starts in the wall of the intestine, but we don’t know what starts that process,” Rowson states. “Maybe the diet the cow is consumingor her intestinal motility contributes?” Although it is more common in the fall and winter, HBS can happen any time of the year. Bascom says this is likely a result of dairies starting newcrop feed coupled with inadequate fermentation. Feed management goes beyond silage, and Bascom reminds producers that mold can occur in other feedstuffs. “Silage management practices at harvest and feed out can minimize the growth of molds,” Bascom says. “At harvest, put it up at the right moisture, pack it and cover it. At feed out, manage the face to reduce mold growth and avoid feeding moldy silage.”

HBS Symptoms Diagnosing HBS based on clinical signs alone is generally not possible, because these symptoms can also be found in other diseases. Clinical symptoms connected with HBS include:

  • Sudden onset of depression.

  • Dehydration.

  • Decreased feed intake and milk production.

  • Abdominal distension and pain.

  • Either no feces or a decreased amount of feces that are dark and contain clotted blood

An additional symptom associated with HBS is cold extremities. A rectal examination may reveal distended loops of the small intestine or even no stool, due to the blockage. Often, most cows appear to be in good health before the development of this disease, hence the name of “sudden death disease,” as many times a producer finds a cow down or even dead.

Rowson notes that often HBS is either under- or over-diagnosed, and she says the latter is frequently the case. "Producers do not perform a necropsy and chalk a sudden death cow to hemorrhagic bowel syndrome," she says.

A proper diagnosis is often made through necropsy, while ultrasound is only able to make a definitive diagnosis of HBS a quarter of the time. Exploratory surgery is needed to confirm and treat HBS, but this can be expensive and is time-sensitive, as cows would need to be rushed to a veterinary medical school.

Rowson notes that statistics show that the University of Wisconsin veterinary school has a high success rate with surgical treatment, but they have also reported a high rate of recurrence, with nearly 40% recurring within the first 12 months. “We don’t know exactly why some cows that survive the initial surgery develop HBS again. It’s been speculated that there might be a genetic predisposition to HBS or maybe, management practices designed to achieve high milk production increases the risk of developing HBS, and these cows are going right back into that environment,” Rowson states.

Management Tips Make no assumptions, Rowson advises. When a cow dies of what is believed to be HBS, “open her up,” she says. “It could be a Hardware Disease or abomasal ulcers or something else.”

Bascom agrees and says producers? that feed additives can’t properly evaluate whether the product is helping minimize HBS if they don’t accurately know why cows are dying. “Oftentimes, producers might make an abrupt change to the ration, taking out a supplement because they feel like it's not working,” Bascom says. “However, without performing a necropsy, they easily could be dealing with a completely different cause of death.”

Recommended management tips to help prevent HBS:

  • Make sure feed is in front of the cow 22 to24 hours a day.

  • Push feed up frequently.

  • Prevent sorting and slug feeding.

  • Ensure enough fiber is in the ration.

  • Use a consistent time for feeding, day-after-day.

  • Limit spoilage with haylage and corn silage by ensuring proper fermentation, packing right, chopping at the optimal moisture level, using an inoculant.

  • Remove mold before feeding – pitch the crust on the silage and side walls.

Takeaway Advice Both Rowson and Bascom encourage limiting stressors that cows encounter. In addition to monitoring feed quality, be sure to evaluate and manage the cow’s environment for potential stressors. Excessive cow movements that disrupt an established social order can cause cows to go off feed. Minimizing overcrowding, focusing on cow comfort and keeping heat stress at bay can lead to a less stressed cow and, therefore, help her maintain an overall healthier immune.

Furthermore, minimizing the stressors that cows are subject to, especially around the time of calving and early stages of lactation, is essential. Bascom notes that some cows are more susceptible to the effects of stress than others which can affect immune function and predispose cows to developing HBS as well as other disorders.

Several feed additives are in the marketplace claiming to boost the immune system.


While feeding additives can help boost immune health, Bascom reiterates that identifying and minimizing stressors is key. “A cow can live in the best environment and still be exposed to stressors during a normal lactation cycle, because events such as calving and dry off are stressful,” Bascom adds. “Try to recognize and manage the stressors, so when a cow experiences stressful events, like calving, she is better positioned to handle that stress.”

To better understand this fatal intestinal disease that could be impacting your herd, don't make assumptions. Learn what the true cause is behind the death of any cow, and then manage the symptoms from there.


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