Rotavirus in Calves

May 2012
Rotavirus infections cause severe scouring and death in very young calves, at great cost to the dairy and dairy beef industries. Calves get early protection through the colostrum of vaccinated cows, but on some farms disease in newborn calves is still observed. Through molecular techniques, Dr Howe and colleagues at Massey have determined that at least two strains of Rotavirus are present in NZ cattle. Vaccines are now available in New Zealand to protect against both strains of virus. A third strain has been found in humans in the South Island, and further work is needed to determine whether it is also present in New Zealand cattle.

Rotavirus infections are responsible for nearly half the cases of severe scouring in young calves, which often results in death. Of the 3.6 million dairy calves born, about 2 million are reared as replacement heifers or bulls/steers for the dairy beef industry. Thus the cost of a Rotavirus outbreak is high, and is estimated at an average of $6000 per dairy farm per season.

Calves can derive immunity from the colostrum of cows vaccinated against Rotavirus, and suitable vaccines have been available for some years. However, there have been some farms where serious infections have occurred despite a vaccination programme.

Dr Laryssa Howe and her team at the Institute of Veterinary, Animal and Biomedical Sciences (IVABS), Massey University, were funded by a commercial vaccine supplier to study samples from farms where rotavirus scours had been diagnosed in spite of vaccination. Overseas some 15 different strains of Rotavirus A have been identified in cattle, and vaccination against one does not always give protection from others. The most common strains causing diarrhoea are known as G6, G10 and to a lesser extent, G8. The initial vaccines available in New Zealand contained only the G6 strain.

Dr Howe extracted viral nucleic acid from the samples sent to her for molecular analysis and antibody work to determine the Rotavirus serotype. As suspected, the Massey team found G10 as well as G6 in the analysed samples. This information has lead to the New Zealand release of a rotavirus vaccine containing both G6 and G10 strains.

Weve found local variations in serotypes, particularly in the Bay of Plenty, Taupo and the East Coast regions where both the common G6 and the less common G10 strain are present. However, it currently appears that the rest of the North Island only has the G6 strain, says Dr Howe.

At the moment we think there are only two serotypes in New Zealand cattle G6 and G10 but we havent examined the strains circulating in the South Island yet. Interestingly, New Zealand medical researchers have found a cattle G8 strain in the South Island in the human population. This suggests that the G8 strain may be in New Zealand, particularly in the South Island. Due to the high level of agriculture undertaken in New Zealand there is the possibility that the cattle G8 strain has infected humans sometime in the past.

Rotavirus can cause severe gastric upsets in humans, particularly children, but Dr Howe says that generally the human and cattle strains are distinctly different and crossover is rare. However, there has been some research overseas suggesting that countries with higher cattle farming concentrations, especially dairying, appear to have a higher rate of Rotavirus in humans and include some rotavirus strains which may come from cattle.

Humans and animals usually develop a protective level of immunity after being infected with Rotavirus. Most people are infected with rotavirus before their fifth birthday, however if in the rare event they are then infected with a crossover cattle strain, the disease can be quite severe regardless of age or prior exposure to human rotavirus strains.

In order to provide the best protection for calves and limit costs related to rotavirus disease, dam vaccination is critical to improve the degree of protection to calves provided the vaccination is timely and calves also have access to adequate levels of colostrum within the first 12 hours of life. Heifers need to be given an initial shot earlier in the year followed by a booster about 3 weeks before calving. Cows that have been vaccinated in previous seasons need only the 3-week booster to raise the concentration of antibodies. In addition, the use of commercial colostrum products containing Rotavirus antibodies are available for administration to milk-fed to calves which can also be very beneficial.

If there are any concerns about rotavirus disease in calves, development of an appropriate vaccination schedule and management of milk-fed calves, it is important to consult with your local veterinarian for advice.