Calf diarrhea (scours) is the primary cause of death in calves from 2 to 30 days of age. And, while advances in scours treatments may bring improved survival rates, the economic benefit of improved preventive measures far exceeds that of treatment.
Scours pathogens are viruses, bacteria and microscopic parasites. Most of these pathogens do their damage in the intestinal tract. Several mechanisms go to work there, all of which cause diarrhea or scours.
- They cause the cells of the intestinal lining to malfunction.
- They can kill the intestinal lining cells.
- They can invade the deeper layers of the intestinal lining and rapidly destroy it.
The K99 strain of Escherichia coli (E. coli) causes diarrhea by impairing the ability of the intestinal lining to digest and absorb the milk nutrients. This K99 strain, however, is only capable of causing scours in calves under a week old. After that, the calf's intestine becomes resistant to its effects.
The cells lining the intestine can be killed by viruses such as rotavirus and coronavirus and a protozoan parasite called Cryptosporidium. The scours tend to be yellow and watery. Because viruses and cryptosporidia aren't susceptible to antibiotics, the only treatment of this type of scours is nutritional and fluid support of the calf until the intestine lining is regenerated.
Carriers And Shedders
Rotavirus, coronavirus and crypto are carried by healthy heifers and cows and are shed into the environment in their manure. Cryptosporidium, which is also a threat to humans, is particularly troublesome because no effective treatment nor vaccine is available, despite extensive research.
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Bacteria, such as certain strains of E. coli and Salmonella, invade the deeper layers of the intestinal lining, rapidly destroying it. Generally, this group causes release of blood and mucus into the diarrhea.
Calf scours are usually caused by two or more of these pathogens working together. The severity and duration of a scours episode is related to the following factors:
- The number (or dose) of each agent involved (i.e., sanitation).
- The extent of intestinal destruction or malfunction created by each pathogen -- their effects are additive. Different strains of each pathogen exist, and differ in their capacity to induce severe disease.
- The amount and quality of colostrum consumed by the calf from the dam. *The severity of other stresses (wetness, cold, need to fight off other diseases and poor nutrition caused by poor maternal milk production or deficiencies of certain trace minerals or vitamins).
After The Damage Is Done
When the intestine is damaged by scours pathogens, the water and nutrients in the dam's milk can't be completely absorbed into the calf's bloodstream. As a result, a large fraction is lost from the calf's body in the diarrhea. This loss is the greatest threat to the survival of a scouring calf. Therefore, it must be a primary treatment focus.
The fluids lost in the diarrhea quickly deplete the calf of water and salts, producing symptoms of dehydration -- sunken eyes, weakness, and dryness to the mouth and nostrils. As the calf loses body fluid through diarrhea, its blood thickens, making it harder for its heart to deliver blood to its tissues.
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Meanwhile, the loss of salts from the calf's body creates an imbalance in the normal pH of the calf's system. As acidity takes over, acidosis sets in.
Calves with acidosis are weak and uncoordinated, often exhibiting a drunken, wobbly gait when made to walk. When encouraged to nurse, their suckle response is just a weak chewing motion. As acidosis worsens, the calf can't stand, becoming lethargic and sleepy.
Very advanced cases become comatose. The function of the heart and lungs is greatly impaired in cases of acidosis, and many advanced cases die of cardiac arrest.
Low Blood Sugar
For scouring calves, another common problem in cold weather is low blood sugar. The calf expends its own sugar reserves trying to keep warm. If it can't absorb milk nutrients from its damaged intestine, its sugar reserves aren't replenished.
Calves with low blood sugar usually develop subnormal temperatures (below 100 degrees F) as they lose the ability to maintain body heat. Low blood sugar contributes to the symptoms of weakness and lethargy induced by acidosis.
Thus, several problems are simultaneously at work: dehydration, acidosis and low blood sugar. If the calf didn't get adequate amounts of colostrum the first day of life, simultaneous infections in other organs can also be present.
Treatment involves correcting the fluid deficit and electrolyte imbalance. The use of antibiotics in cases of non-specific diarrhea is controversial within the veterinary profession. Barring a history of Salmonella or signs of systemic infection, such as a swollen navel or swollen joints, the use of antibiotics in non-specific diarrhea of calves is inappropriate. It will usually not affect the outcome, but it rarely makes things worse.
The key to proper therapy is to realize the magnitude of the fluid deficit. A 100-lb. calf that's 10% dehydrated needs 10 lbs. of fluids to just correct the immediate deficit. If 1 gal. of fluids weighs 8 lbs., the calf needs somewhere around 1.25 gals. Giving a calf 2 qts., two to four times a day, may be necessary to correct and maintain the fluids.
Severe dehydration must be corrected using intravenous treatment. In addition, most calves with diarrhea will be acidotic. Electrolyte solutions with an alkalinizing agent such as bicarbonate are then necessary. Carefully read the label to find products that contain bicarbonate. Usually, they're more expensive but are worth it.
Prevention Is Paramount
Remember, scours prevention is the most important and cost-effective area to invest your time. Attack these three broad points:
- Good general hygiene minimizes exposure, thus preventing disease. There are numerous opportunities for improving sanitation. A few include improving the general sanitation of calving lots, disinfecting calving barn pens between occupancy, sanitizing calf treatment equipment between uses and isolating scouring calves.
- Make sure the calf gets enough colostrum. This is the single most important determinant of the calf's immune status during the neonatal period. Failure to do this means a 3- to 10-fold increase in the calf's risk of becoming sick.
- Proper cow vaccination against E. coli and rotavirus and coronavirus can increase the antibodies she passes through her colostrum to the calf.
The complex, interrelated nature of these strategies makes prevention a challenge. For example, implementing a sound vaccine program (prevention strategy 3) will be totally ineffective if calves don't suckle enough colostrum (prevention strategy 2).
Likewise, even if you accomplish prevention strategies 2 and 3, if the environment in which the calves are born is heavily loaded with scours pathogens (strategy 1), it will overwhelm the calf's immunity and scours will result.
Scours is one of several management disease complexes where integrated prevention strategies and attention to detail in multiple areas are required for success.
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