Bloat is a common disorder seen in ruminants, such as cattle. However, bloat observed in young calves is very different from bloat seen in cows. According to Smith (2010), bloat in cows is a result of free gas building up in the rumen (the first component of the bovine’s stomach) and causes distention, or enlargement, of the rumen. This distention of the rumen can impair breathing and result in suffocation of the animal. In contrast, bloat in young calves results from gas build-up in the abomasum, the last of the four compartments of the bovine’s stomach (Smith, 2010). The abomasal bloat observed in young dairy calves is often referred to as Acute Bloat Syndrome (ABS). In a survey conducted by Shoemaker et al. (2007), 276 veterinarians across the country reported ABS to occur on a median of four farms per practitioner. ABS is becoming a widely occurring syndrome, and it is important that dairy farmers are aware of this disorder and remain updated on current research. In order to better understand ABS, it is necessary to know which cattle can be affected, the symptoms associated with the syndrome, the potential causes, the treatments, and the preventative measures for ABS. 

Acute bloat syndrome occurs in calves. In most cases, calves are usually 4 to 21 days of age (Shoemaker et al., 2007). According to Marshall (2009), ABS occurs sporadically in dairy calves. Some farms will have multiple cases of ABS at one time. Not only is it a good idea to know when calves are susceptible to ABS, but it is also important to recognize the symptoms.

Understanding the symptoms of ABS is critical because calves that develop the syndrome often die within 6 to 48 hours. According to Van Metre and Callan (2006), the case fatality rate is a very steep 75 to 100%. Although the likelihood of saving the calf is low, it is only possible if symptoms are recognized early. Symptoms of ABS include abdominal distension, depression, colic signs, grinding of teeth and salivation, anorexia, fluid slosh in the abdomen, and dehydration. Less common symptoms include diarrhea and high temperature (Shoemaker et al., 2007). According to Panciera et al. (2007), after experimental induction of ABS in calves, the necropsy showed distention, hemorrhage (internal bleeding), inflammation, mucosal necrosis, and mural emphysema (air build-up in the wall of the stomach). The symptoms of ABS usually include a rapid onset and sometimes are not even observed before death occurs. Calves will eventually die from shock or compromised respiration due to the enlarged stomach, according to Van Metre (2017).

The causes of ABS are not well understood; however, experimental induction of ABS in calves led researchers to believe that the cause of ABS is large quantities of highly fermentable carbohydrates and high concentrations of bacteria containing enzymes capable of fermenting the substrate (Panciera et al., 2007). As a result of these two factors, high levels of gases are produced in the abomasum, causing distention. Although researchers are not certain which exact species of bacteria cause ABS, Clostridium perfringens, Sarcina spp, Streptococcal spp, Escherichia. coli, and Salmonella typhimurium have been identified in the abomasum of affected calves. Further research must be done in order to determine the specific role these bacteria play in ABS. Other factors that can contribute to ABS are related to nutrition and include high volumes of milk replacer, cold milk, high osmolality of milk, high protein  and fat contents in milk, high-energy oral electrolyte solutions, and inconsistent feedings. All of these can cause a slower emptying rate of the abomasum. According to Burgstaller et al. (2017), feeding practices that significantly prolong abomasal emptying can increase rates of gastrointestinal diseases in calves.  This is because the bacteria have more time to ferment the feedstuff, thus producing more gas in the abdomen. Familiarity with these causes of ABS will aid in proper decision-making regarding treatment and prevention of the disorder.

Measures for controlling ABS mainly involve dietary management in lieu of medications or procedures (Marshall, 2009). There are no reliable data on whether or not conventional vaccines are helpful. It is thought that vaccines containing inactivated toxins given to pregnant cows will produce antibodies in the colostrum and help protect the calf (Van Metre, 2017). Antibiotics, such as penicillin or oral Beta-lactam which would target Clostridium spp, can be used, but these are not the best treatment option because the species of the ABS-causing bacteria may be different. Other medications that can be given include rumen tonics and anti-inflammatories (Shoemaker et al., 2007). Bloat-relieving procedures, such as placing a stomach tube or puncturing the abomasum to release air, are not necessarily effective treatment options. Since a stomach tube cannot reach the abomasum, the calf’s front end must be elevated in order to allow the gas to pass to the rumen and out the tube (Van Metre, 2017). Puncturing the abomasum must be done while the calf is dorsally recumbent (lying on its back) because there is a high risk of leakage of abomasal contents into the abdomen (Marshall, 2009). For these reasons, procedures and medications are usually not the best treatment options. Dietary management strategies are the preferred ways to prevent ABS. These include feeding the calves multiple, small meals on a consistent basis, mixing the milk replacer correctly according to manufacturer’s instructions in order to lower osmolality, feeding warm milk, and providing adequate amounts of water (Smith, 2010). These dietary management strategies are easy to apply and will increase the passage of feed through the abomasum to the small intestine. Although these are good treatment options and preventative strategies, farms that were rated good to excellent, based on their management practices, still struggled with ABS.

ABS is a spontaneous and puzzling disease that affects many dairy farms. The calves at risk for ABS, associated symptoms of ABS, the potential causes of ABS, and the treatment and prevention of ABS are important factors that must be studied and understood. Unfortunately, there are still many uncertainties and unknowns about this disorder, and further research is needed in order to learn more about the syndrome and the specific species of bacteria that cause it.

Works Cited