Hemorrhagic bowel syndrome (HBS) can kill apparently healthy cows in 24 to 36 hours, according to Dr. Mary Beth de Ondarza, a dairy nutritionist from New York. De Ondarza spoke Tuesday at Alltech's 24th International Animal Health and Nutrition Symposium in Lexington, Ky.
What is hemorrhagic bowel syndrome (HBS)?
In the last 15 years, hemorrhagic bowel syndrome has become a greater concern in regard to sudden death of mature dairy cattle. HBS is usually fatal and can affect apparently healthy cows with little or no warning, de Ondarza explains. "Early postmortem examination of cattle with HBS shows intestinal lesions with hemorrhages and clots. The size of the intestinal lesion can vary between 6 inches and 30 feet. Fluid may accumulate before the blockage. Death is the result of the obstructed bowel, blood loss, and a resulting anemia."
According to de Ondarza, it usually kills only a single cow in a herd, it's usually the "best cow" that is most vulnerable to contract the mysterious disease. While there are often no symptoms, some symptoms include depression and loss of appetite.
What causes HBS?
Clostridia perfringens type A is consistently found in the intestinal tract of healthy animals and in the environment, whereas types B, C, D, and E are not. Because of this, type A was historically considered less toxic. It is believed, however, that problems can occur when the growth rate of type A suddenly increases to produce toxins that facilitate the development of intestinal lesions, de Ondarza says.
"These bacteria can digest starch and if large amounts of starch reach the intestine and intestinal pH changes, their growth rate can be affected. Studies have found a positive relationship between rumen acidosis, which facilitates the passage of more starch to the cow's intestine, and HBS," she adds.
Rumen function is optimized when rumen acidosis is controlled, de Ondarza adds. With a more functional rumen, less starch will escape to the intestines to support the growth of undesirable bacteria. Often, HBS problems can be reduced by adding more effective fiber to the diet, reducing overall starch levels in the ration, and more carefully mixing the TMR. Feed additives may also play a role in improving rumen digestion. Starch passage to the hindgut is not only dependent on rumen functionality but is affected by starch texture, moisture content, processing technique and endosperm type. Starch passage will increase with increasing particle size and dry matter content.
"Even with good dietary management and no rumen acidosis, high-producing dairy cattle as well as young calves digest a significant amount of ration nutrients in their intestines."
This situation increases their risk of intestinal proliferation of undesirable organisms. A disruption in intestinal microbial balance can promote the growth of pathogenic bacteria. Microbial additives can be used to improve the balance of intestinal bacteria and may bind pathogens.
HBS has also been associated with feeding moldy forage or grain with higher levels of Aspergillus fumigatus, a common soil microbe. However, an association between levels of Aspergillus fumigatus in blood and HBS does not prove a causative relationship, de Ondarza says. "HBS may result in greater amounts of Aspergillus fumigatus in the blood simply due to increased absorption of the mold when the bowel is hemorrhaging. Feeding mold inhibitors and mycotoxin binders has reduced the incidence of HBS on some farms. However, this does not prove the bacteria is the primary cause of HBS in these situations. The mold and associated mycotoxins may simply be affecting the rumen ecosystem. Once mold and mycotoxin levels are reduced, rumen digestion and intake improve, and slug feeding is reduced. This decreases the likelihood of a high starch load to the intestines that could accentuate the growth of undesirable organisms such as Clostridia perfringens type A."
"Since higher levels of intake and production are often associated with increased farm profitability, the dairy cow's intestine will continue to gain a more prominent role in the digestive process even when the rumen is functioning well," de Ondarza says.
With that, undesirable organisms will continue to be a threat, she says. Digestive models of nutrient flow to the hindgut need to be improved. The impact of nutrition on growth of intestinal bacteria populations needs to be understood better. Feed additives show promise in controlling clostridial disease. The benefits of lactobacillus have been shown in laboratory cultures, humans, and calves but there has been little controlled research to confirm their benefits in adult ruminants, especially for control of HBS. Mannanoligosaccharides may also perform a role in prevention of clostridial diseases but more in vitro and in vivo research is needed in this area. Feeding a direct-fed microbial product composed of 10 billion CFU's of Lactobacillus bacteria in addition to mannan oligosaccharides appeared to reduce the incidence of HBS in some high-producing dairy herds.