While a distended abdomen can certainly happen in calves of all ages, a true ruminal bloat is not common in young calves—even though visual signs might indicate otherwise.
“We don’t usually see ruminal bloat in young calves, due to minimal ruminal development before about five weeks of age or so” explains Sarah Depenbrock, DVM and Assistant Professor of Clinical Livestock Medicine at the University of California-Davis School of Veterinary Medicine.
There are many different causes of abdominal distension, and many possible predisposing underlying factors for those causes. To determine the cause of what you’re seeing on the farm, she says to put on your detective hat and prepare for some systematic sleuthing.
Start by thinking actively about the full triad of disease factors – the host, any pathogens and the environment.
“Do a thorough diagnostic investigation – not just into the anatomic or infectious cause of the distension – but also look for any underlying host or environmental factors that led to the current problem; often there is a herd management intervention that can be recommended for prevention” she says.
Here are four practices Depenbrock uses to help identify the underlying cause of distended abdomen in calves.
1. Collect a history and do a thorough physical exam. This sounds pretty simple, but the physical exam with an informed history may be the most valuable diagnostic test you can run. A big step in solving a distended abdomen is consideration of all the anatomic structures and spaces within the abdomen. A through physical exam uses simple techniques such as observation of the abdominal contour and auscultation/percussion/succussion to elicit evidence of what abdominal organ or fluid space is distended. Also, look at the rest of the animal’s clinical signs. Is this an animal that needs fluid therapy or surgery urgently? Are there other abnormalities that hint at an underlying cause, or comorbidities that suggest a poor prognosis?
“If you're presented with a dead animal, then your necropsy exam on the dead animal can also be very valuable,” Depenbrock says.
If you suspect a gastrointestinal (GI) disease is present, necropsy the animal as soon as possible after death, and pay attention to size and position or GI structures. “The reason is that the GI tract tends to autolyze very quickly and affect our ability to interpret GI changes,” she explains.
(Figure 1): Possible causes of a distended abdomen in calves broken down by anatomic site (This content is based on the AABP New Grad Conference proceedings, Neonatal Distended Abdomen by Depenbrock.)
2. Use ancillary diagnostic tests to confirm diagnostic hypotheses from the physical exam. Even in a field setting, there are some practical ways you can narrow down the list of causes of abdominal distension. For example, passage of an orogastric or nasogastric tube may find foul-smelling, abnormal ingesta in the rumen which suggests proximal GI disease. Obtaining and examining a fluid sample is a relatively simple test that can be useful in the field or in hospital to help narrow down a list of differential diagnoses. The rumen is sampled via passage of a tube or percutanteous rumenocentesis, the abomasum can be sampled via percutaneous abomasocentesis, and free fluid in the abdomen can be sampled using abdominocentesis at a dependent site (usually sampled from the right caudoventral abdomen if diffuse fluid accumulation is present). With any percutaneous fluid sampling technique, use of aseptic technique to avoid abdominal contamination is important. Several simple tests, in addition to gross appearance and smell, such as pH, lactate and microscopic examination, can be run on the fluid sample and choice depends on the source of the fluid and the differential diagnoses. Your reproductive ultrasound setup can aid in finding a location for fluid sampling and is an efficient and practical method for screening for some common abdominal conditions and is often Depenbrock’s first go-to tool in the field.
“If I'm not sure from my physical exam, splashing and pinging where the source of the of the distension is coming from, I can put my ultrasound probe on and easily recognize what is a fluid-filled abomasum or rumen based on the mucosal fold structure versus what is free fluid in the abdomen versus fluid-filled or amotile intestines,” she says.
Depenbrock says even the linear rectal probe can help you with a basic evaluation in calves if you don’t have an abdominal probe. Although the rectal probe typically has less penetration than an abdominal probe, it can still be used transabdominally for a limited evaluation in a calf since the calf’s abdominal wall is typically thin enough to make some basic assessments such as between GI viscuses (abomasum vs. rumen vs. intestine) vs. free fluid.
One tough diagnosis can be confirmation of ruminal drinking. In a healthy, pre-weaned calf, the esophageal groove closes and shunts most of the milk into the abomasum for digestion. If the calf is a ruminal drinker, there's some dysfunction in the process that allows milk to pass into the rumen where it ferments abnormally and causes indigestion, variable degrees of abdominal distension and chronic ill thrift. You can use your ultrasound probe transabdominally while the calf drinks, or right after, to check for abnormal fluid accumulation in the reticulo-rumen. The technique has been previously described in detail by Braun et al 20132. Running blood work (such as serum electrolytes, blood gas, or a CBC and chemistry) can also be helpful in cases of abdominal distension, if available, and may also help diagnose comorbidities, plan fluid therapy and help prognosticate.
3. Revisit the history once you have a clinical diagnosis. For GI lesions, collect a thorough history of feeding practices from birth up through the age group affected in the current investigation. Focus closely on any human interventions or processes involved with feeding practices in calves. If abomasal bloat is occurring in bottle fed calves, it is critical to examine the details of the milk feeding process from bottle sanitation, feed preparation, through delivery of bottles and consumption of milk. Finding the culprit in a given case isn’t the end. Many causes of abdominal distension may reflect underlying herd management problems. For example, if ruminal bloat is being diagnosed in weaned calves, it is imperative to sort out if there is a problem with the starter diet leading to improper ruminal development or indigestion. Or, there could be an underlying respiratory disease responsible for poor ruminal motility, and the observed indigestion may really be secondary to a calfhood pneumonia management problem.
4. Tie it all together for the client. Make specific, achievable and measurable goals for change. Making a diagnosis, and treating affected animals is just part of the puzzle. Going a step further, creating actionable recommendations for prevention and checking in on progress add value to the service you provide producers.