Age of onset provides clue to cause of diarrhea in calves

Several bacterial agents can cause calf diarrhea, and most of these agents tend to result in calves getting diarrhea within the first week of life. | File photo

Calf scours, or calf diarrhea, continues to be one of the significant causes of calf mortality in beef cattle herds.

Dr. Jennifer Pearson from the University of Calgary published data from the Western Canadian Cow-Calf Surveillance Network that documented an overall pre-weaning calf mortality level of 4.5 percent and a pre-weaning treatment rate for all diseases of 9.4 percent.

In that study, three percent of the calves were treated for neonatal calf diarrhea, which was the second highest reason for treating calves and just slightly lower than respiratory disease.

An older study from the National Animal Health Monitoring Service in the United States had similar findings with 2.4 percent of calves treated for diarrhea before three weeks of age and 1.7 percent of calves treated at older than three weeks of age.

The term calf scours or neonatal calf diarrhea is a type of “syndromic diagnosis.” This syndrome of calf diarrhea is characterized by the clinical signs of watery feces, increased frequency of bowel movements and a resulting dehydration and electrolyte loss.

We are lumping all the potential infectious and non-infectious causes of enteritis or inflammation of the intestinal tract in young calves into one large category. However, there are actually many different infectious agents that can cause calf diarrhea and in some cases they can be in combination.

One clue that may help to narrow down the cause is the age of the calf at the onset of disease.

There are several bacterial agents that can cause calf diarrhea and most of these agents tend to cause calves to get diarrhea within the first week of life.

E. coli bacteria are one of the more common bacterial causes of calf diarrhea in very young calves. There are specific strains of these bacteria that can infect young calves and can cause severe diarrhea and dehydration quite quickly.

We have vaccines for these strains of E. coli, which we can give to the cow, and they are fairly effective in protecting the calf, provided that the calf consumes adequate colostrum within four to six hours of birth.

However, any vaccine can potentially be overwhelmed if the infection pressure is too severe.

Salmonella bacteria are another important cause of diarrhea in young calves and they also have multiple strains that may have very different presentations.

The age range here is a bit broader and so might be less of a clue in identifying the pathogen because it can cause diarrhea in calves from two to 12 weeks of age. Salmonella dublin is a strain that has risen in importance in North America over the past number of years and it can have additional manifestations such as pneumonia and septicemia in young calves and abortion in cows.

It is important to note that the bacterial causes of diarrhea are the only ones in which antibiotics are going to have any significant benefit in the treatment approach.

The viral causes of diarrhea include primarily rotavirus and coronavirus. Both of these viruses tend to cause diarrhea in calves that are a little older than E. coli cases, most commonly at one to three weeks of age.

Both of these viruses tend to damage the lining of the intestinal tract, making it difficult for calves to absorb fluid and as a result cause diarrhea.

These two viruses are probably some of the most common causes of calf diarrhea and often responsible for many of the scours outbreaks that we see in beef cattle herds.

Most of our calf scours vaccines include rotavirus and coronavirus along with E. coli, and they will provide colostral antibodies to these infectious agents, again dependent on the calf getting colostrum within the first six hours of life.

The parasitic causes of diarrhea in calves are mostly attributable to two different single celled parasites called Cryptosporidium and Coccidia. Cryptosporidiosis is seen in a fairly broad age range of calves from five to 35 days of age and is often seen as a persistent diarrhea that does not seem to respond to therapy.

It can often occur in combination with the viral infections. It tends to be a bit more common in dairy calves, but it also has a significant impact on some beef herds.

Cryptosporidiosis should not be confused with coccidiosis, which tends to be a cause of diarrhea in older calves that are at least three weeks of age and can occur up to a year in age.

In suckling calves, coccidiosis tends to occur around three to six weeks of age and the calves may have blood in their feces and strain when they defecate.

When treating any cause of calf diarrhea, the most important therapy involves correction of the dehydration as well as addressing the potential drop in blood pH or acidosis that occurs because of the loss of electrolytes through the damaged intestinal tract.

Calves that are able to stand and are slightly dehydrated can probably be treated with just oral electrolyte solutions.

There are lots of good commercial products available and your local veterinarian can help you choose an appropriate product if you need some on hand. If the calf is unable to rise and has more moderate or severe dehydration, these cases probably have a more severe drop in blood pH and may require intravenous fluids and electrolytes in order to correct the deficits at this stage of the disease.

It’s important to recognize that the vast majority of diarrhea cases have a primary fluid and electrolyte deficit and that antibiotics are only going to help in those cases with bacterial infections. Antibiotics do not work against viruses.

We don’t always need to know the cause of the infection that causes calf diarrhea to help prevent it from occurring, but it does help to sort out the correct treatment.

The principles of providing appropriate vaccines to the cows, ensuring all calves get colostrum within the first six hours, making sure cows calve in a clean environment, preventing crowded conditions and calf to calf spread of infections will all help to prevent calf diarrhea regardless of the infectious agent.

John Campbell is a professor in the department of Large Animal Clinical Sciences at the University of Saskatchewan’s Western College of Veterinary Medicine.

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