Also known as
Rotaviruses are the most common cause of diarrhea in very young calves. Bovine rotavirus belongs to the family Reoviridae. The virus is present in most cattle herds and typically causes diarrhea in calves between 4 to 14 days old, sometimes up to 3 weeks of age.
These viruses are present in the environment and nearly all cattle have come into contact with them; most adult animals have antibodies and are immune to the effects, whereas baby calve with no immunities are very susceptible.
The intestinal tract is the site of multiplication, and these viruses are excreted only in feces. The feces of infected calves contain large numbers of rotavirus and quickly contaminate the environment, to be picked up by susceptible calves.
Clinical disease in calves older than one month is rare. However, periodic re-infection (without signs of disease) and virus shedding occurs in older cows and calves.
The diarrhea usually lasts 4 to 8 days. During this time calves can become dehydrated and pick up secondary infections and these combinations can sometimes be fatal without treatment.
- Sudden onset of profuse liquid diarrhea—often pale yellow and containing mucous and flecks of blood
- Sometimes off feed
Rotavirus was first identified in the U.S in 1969 and thought to be the cause of outbreaks of diarrhea in beef calves in Nebraska. Since then, this virus has been found in calves with diarrhea in many countries, and is the most common viral cause of diarrhea in calves and lambs worldwide.
Groups A and B rotavirus are involved, but group A is most prevalent and clinically important and contains several serotypes of differing virulence.
The factors that influence rotavirus infection and severity include the age of the calf, immune status of the dam, how much antibody was obtained via colostrum, ambient temperature (weather stress), level of exposure to the virus, presence of other pathogens (rotavirus infections are often accompanied by coronavirus and E. coli in calves over 4 days of age), and level of stress.
Mortality rates are highest in the youngest animals that received insufficient colostrum and are subjected to severe weather stress.
Healthy adult cattle may be carriers and periodically excrete the virus in feces. Excretion may increase around the time of calving and be more frequent in first-calf heifers. This can lead to contaminated calving areas and infection of the udder and perineum of the dam.
Other sources of infection include feces of healthy calves and especially feces of diarrheic calves, which contain large numbers of the virus early in the course of infection. A few scouring calves in the herd can result in severe contamination of the area. Transmission is primarily by fecal-oral contact,
Incubation period (from ingestion of the pathogen until breaking with diarrhea) is 10 to 24 hours. Levels of antibodies in colostrum are lower in first-calf heifers, and their calves are at risk for higher incidence of disease and higher rates of mortality.
Rotavirus replicates in the absorptive and enzyme-producing enterocytes (absorptive cells that line the intestine) on the villi of the small intestine, leading to rupture and sloughing of those cells, with release of more virus to infect adjacent cells. With virulent strains of rotavirus, the loss of enterocytes exceeds the ability of the intestinal surface to replace them; thus there is a decrease in intestinal absorptive surface area and intestinal digestive enzyme activity.
Viruses usually produce diarrhea by destroying these absorptive cells of the mucosal lining, as well as causing inflammation. Unable to absorb fluids and nutrients (with everything passing on through the tract) the calf soon becomes weak and dehydrated.
Diarrhea due to rotavirus, coronavirus, and other viruses usually is seen in calves 5–15 days old but can affect calves up to several months of age. Affected calves are only moderately depressed and may continue to suck or drink milk, but remain dehydrated.
The feces are voluminous, soft to liquid, and often contain large amounts of mucus. Diarrhea commonly persists for at least 3 days and often longer. Cases of viral diarrhea that are uncomplicated by other pathogens commonly respond within a few days to fluid and electrolyte therapy and adequate nutritional support.
These viruses are resistant to commonly used disinfectants so it is difficult to prevent contamination of barns, calf shelters, etc. once these pathogens have been introduced. However, it is still very important to try to keep calves’ environment clean, and isolate any calves with diarrhea from the rest of the group. All young calves under 3 weeks of age are highly susceptible to infection.
Early immunity in new-born calves depends almost entirely on their obtaining antibodies via colostrum. The transfer of antibodies via colostrum is the single most important form of protection of the new-born calf.
Ensuring that calves receive sufficient colostrum (at least two quarts within the first six hours) is vital in the control of calf diarrhea, and continued consumption of colostrum through the first day or two of life is helpful since the antibodies are protective within the gut after the calf can no longer absorb antibodies directly into the bloodstream.
However, this protection lasts for only three to four days, so it generally only reduces rather than eliminates rotavirus diarrhea. This explains why rotavirus infection generally occurs after about 5 to 7 days of age (and even earlier in calves that did not receive colostrum). Continued colostrum feeding can extend this period and reduce the risk.
Vaccines are available for pre-calving administration to the dam to increase the amount of rotavirus antibodies in colostrum. Levels of antibodies in the colostrum often can be high enough to result in a protection period of about 7 days if the calf ingests colostrum within 12 hours of birth.
For farms with a severe rotavirus problem, continued feeding of colostrum from vaccinated dams can extend this period still further. Oral vaccines given to calves immediately birth have been used, but have not proven to be highly effective.
Because of the complex nature of diarrhea in very young calves, it is unrealistic to expect total prevention. The incidence of clinical disease and fatality rate depend on the balance between levels of exposure to infectious agents and resistance in the calf.
Degree of exposure can be reduced by isolating sick animals or by moving calving and calf rearing to a separate area, and by practicing good general hygiene.
Nonspecific resistance should be maximized by providing good nutrition to the dam and assuring that newborn calves consume adequate amounts of high-quality colostrum, preferably within 2 hours and definitely within 6 hours of birth, followed by equivalent amounts at 12-hour intervals for the next 48 hours.
Specific resistance of the newborn can be increased by vaccinating the dam or the newborn.
Some calves do not obtain adequate amounts of antibodies because of delayed sucking or feeding, ingestion of an inadequate volume of colostrum, or ingestion of colostrum of inferior immunoglobulin concentration. In calves that are unable to suckle on their own, administration of 2 to 4 quarts of colostrum by esophageal feeder within the first 2 hours of life can be very helpful.
In a scouring calf, therapy can and should be started even before a diagnosis (regarding the actual pathogen) has been established. Treatment includes fluid therapy (water and electrolyte replacement) and correction of acid-base disturbances, plus antimicrobial and anti-inflammatory therapy.
Fluid and electrolyte therapy is most important and should be started as soon as possible regardless of whether there is evidence of dehydration; clinical signs of dehydration are not apparent until the calf has lost at least 6% of its body weight in fluid.
Calves that are still able to stand and willing and able to suck can usually be treated with oral electrolyte solutions alone. Fluids for oral rehydration should include glucose and amino acids to promote transport of sodium, and should contain sodium, glucose, glycine or alanine, potassium, and either bicarbonate or citrate or acetate as alkalinizing agents.
Several commercial preparations are available. These can be administered by nipple bottle or, if necessary, by stomach tube. These solutions should be administered several times a day until the animal is rehydrated.
In the past, many veterinarians recommended withholding milk from scouring calves, thinking milk would aggravate the diarrhea, but young calves have no energy reserves and have large requirements for energy—and milk provides energy to the calf.
Electrolyte solutions by themselves do not meet calf energy requirements, and milk should not be withheld. The only caution is that milk should not be given at the same time as an electrolyte solution containing bicarbonate since it will interfere with curd formation.
If feeding milk to a calf with diarrhea, wait 2 to 3 hours before giving electrolyte fluid containing bicarbonate.
Calves that are recumbent, weak (unable to stand, unable to suckle), and show evidence of dehydration greater than 8% of their body weight will need IV fluids. These calves are unable to absorb oral fluids and are usually acidotic.
The fluid and base deficits can be corrected initially by rapidly administering a hypertonic solution of sodium bicarbonate (either 500 mL of a 4.2% solution, or 250 mL of an 8.4% solution), followed by a balanced electrolyte solution administered at up to 40 mL per kg of body weight per hour until the fluid deficit is corrected.
Because diarrheic calves are frequently hypoglycemic, adding dextrose to the electrolyte solution is often beneficial in the initial treatment. Oral electrolyte solutions should be used concurrently with and after IV fluid therapy to compensate for ongoing fluid and electrolyte losses.
Although mild diarrhea without systemic disease will not require antimicrobial therapy, use of antibiotics should be considered whenever calves are systemically ill or recumbent to combat possible secondary bacterial infection.
Field studies have shown that at least 30% of diarrheic calves with systemic disease are bacteremic (bacteria in the bloodstream). Because most cases of bacteremia and septicemia in young calves are associated with E. coli, the antibiotic selected should be one that is effective against gram-negative bacteria.
In several studies, severely affected diarrheic calves treated with non-steroidal anti-inflammatory medications in conjunction with fluid therapy showed fewer signs of pain, made faster recovery, and had better weight gains after recovery. These medications help reduce pain, fever and inflammation, and the calves feel better, eat better, and bounce back faster.
The use of drugs such as hyoscine-N-butylbromide or atropine to reduce intestinal motility is sometimes advocated in severe cases of diarrhea, because they decrease fecal output.
There is no research evidence, however, to show if they help or hinder; the veterinary literature does not provide any strong supportive evidence for or against the use of anti-motility drugs.
Intestinal gels and adsorbents, such as kaolin and pectin, are often used, but their only established effect is to increase fecal consistency; they do not reduce the loss of water and ions—but they may soothe the irritated gut.
Oral electrolyte fluids are the most important treatment as long as the calf is still able to absorb them (and is not recumbent). They prevent dehydration, correct acidosis, and replace lost salts. The best electrolytes are far more than just a salt and glucose solution. Ask your veterinarian for advice regarding which oral product to use.
The use of antibiotics to treat calf diarrhea is controversial, particularly if rotavirus is the only cause. Antibiotics will not kill the virus, but can reduce secondary bacterial infection.