Impact of Calf Scours May Reach as Far as the Feedlot

by Teres Gatz-Lambert

Calf scours can wreak havoc with a cow/calf producer's bottom line. But the story doesn't end there as the effects of scours may be so far-reaching that even feedyard performance is negatively affected.

Research results of a study undertaken in the mid1990s by Thomas Wittum, Ph.D., and Louis Perino, D.V.M., Ph.D. show that "inadequate transfer of passive immunity is directly associated with a greater risk of health problems before and after weaning and (is) indirectly associated with preweaning and feedlot growth performance through its effect on morbidity." Calves classified as having inadequate plasma protein concentration - a measure of passive immune status - at 24 hours of age had a greater risk of overall feedlot sickness as well as specific respiratory tract sickness.

Given these findings, cow-calf producers wanting to earn a reputation for supplying top-quality cattle to feedyards may be well advised to provide the feedyard placement market with calves that haven't come down with a bout of scours early in life. On the flip side, feedyards appear to be ahead of the game if their pens are filled with calves that didn't come down with scours early in life.

Viral Infectious Agents
Two viruses have been identified as the major causes of scours: coronavirus and rotavirus.
Rotavirus, which is shed by most adult cattle and picked up by the newborn, can cause scours in calves within 24 hours of birth. When the infection is first introduced into a herd, it can affect calves up to 30 days of age or older. In other herds, rotavirus infection occurs within the first 10 days of life.

The onset of diarrhea is usually preceded by loss of appetite, depression, lack of interest in sucking and occasionally fever. Calves may drool and emit watery diarrhea, with the feces varying from yellow to green. Death rate may be as high as 50%, depending on the secondary bacteria present.

Dr. Don Hudson, extension veterinarian at the University of Nebraska, points out that calves with coronavirus are not as depressed as those infected with rotavirus, and tend to be more than 5 days of age. Another difference between the two viruses: Mortality from coronavirus tends to be less, ranging from 1% to 25%. Although initially producers may have a difficult time detecting any difference in fecal material of calves with rotavirus and those with coronavirus, the fecal material of coronavirus-infected calves that continue to scour for several hours may contain clear mucus that resembles the white of an egg. Diarrhea may continue for several days.

The good news about coronavirus is that it does not have the potential to cause serious outbreaks of diarrhea. The bad news is that coronavirus can act in concert with rotavirus and E. coli.

"Many herds have been found to be infected with both the rotavirus and the coronavirus," Dr. Hudson relates. Dr. Hudson adds that accurate diagnosis of viral scours - which can include the virus of bovine virus diarrhea - can be made only by laboratory tests. He recommends that producers work with their local vet to submit samples that may be most helpful in pinpointing the cause or causes of scours. Samples may include frozen fresh fecal material, frozen intestinal tissue that hasn't begun to decay or possibly a whole dead calf that has not yet begun to decay.

Bacterial Agents
The most common bacterium associated with calf scours, E. coli, is always present in the intestinal tract and is usually the agent that causes a secondary infection following viral agents or other intestinal irritants.

E. coli presents itself in three forms: enteric, enterotoxemic and septicemic. When a calf has the enteric form, diarrhea is present, and the calf tends to die from dehydration rather than infection. The enterotoxemic form - in which toxins released by E. coli quickly cause electrolyte imbalances - is rapid and fatal, and diarrhea usually is not evident. Clinical signs include depressions, failure to get up and a below-normal temperature. Like the enterotoximic form, calves with the septicemic form typically do not have diarrhea. But, before you know it, the deadly active bacteria has invaded the blood stream and penetrated all tissues of the body.

Other organisms associated with calf scours include Salmonella, Cryptosporidiosis and Clostridum perfringens B, C and D. There are more than 1,000 types of Salmonella, and all are potential disease producers.

Treat vs. Prevention
"Treatment for scours is similar regardless of the cause," Dr. Hudson tells. "Treatment should be directed toward correcting the dehydration, acidosis and electrolyte loss. Antibiotic treatment can be given simultaneously with the treatment for dehydration."

To avoid scours and the need for treatment, many producers opt to raise the resistance within their herds while lowering the challenge encountered during the calving season.
Three key management steps help lower the scours challenge in a herd: 1) giving cows and newborns plenty of space during calving season; 2) keeping calving areas as mud-free and manure-free as possible; and 3) separating scouring calves and their dams from the rest of the herd until scours clear up.

To raise the resistance to scours within a herd, pregnant females should be vaccinated with the broadest scour-preventive vaccine available and calves must ingest four quarts of antibody-bolstered colostrum within six hours of birth.

"A good program of adequate nutrition, sanitation, management and a good herd health program are necessary to minimize the incidence and losses," Dr. Hudson summarizes.

"Early diagnosis and treatment will reduce the threat of a herd outbreak. The correct diagnosis is also very important when considering vaccinations and other procedures for the cowherd the next calving season."