BVD Control Begins Long Before You See A Problem
Bovine Viral Diarrhoea (BVD) is sometimes viewed as a dairy industry issue, but the reality is that the disease can have serious consequences for beef breeding herds as well.
Guy Oakley and Sarah Procter, Coastal Vets, Taranaki, worked with Pauline Calvert and Robyn Hirst of MSD Animal Health to help a farming couple identify and manage the risks involved in problems with scours caused by rotavirus.
An outbreak of neonatal calf scours can be challenging and labour intensive, and requires a rapid response from the farmer and vet. In a severe outbreak, calves' response to treatment can be poor and many die; those that recover may have lower productivity because of permanent damage to their gut lining.
Brendan and Megan Forsyth run a family-owned milking herd of 270 crossbred cows on 80ha at Awatuna, Taranaki. They also have a 26ha runoff nearby. For several years scours have recurred sporadically among their calves, consistently caused by rotavirus. With their vet they elected in 2014 to begin vaccinating.
Before calving, the milking herd -- not including the heifers -- were vaccinated with Rotavec Corona. (It is not unusual for heifers to miss rotavirus vaccination, as they are often being grazed away from the farm at the time; and they are naturally mated, their calves not being required as replacements.) Vaccination boosts the dam's lactogenic immunity. This and good colostrum management and neonatal care is critical to managing this common pathogen.
Rotavirus did not appear during the first four–six weeks of calving in 2014, but cases then started to appear and became particularly severe. About ten calves died and the Forsyths struggled to raise enough replacements that season.
MSD Animal Health and Coastal Vets, with the Forsyths, investigated the cause of the outbreak, which occurred despite vaccination. They concluded that overall farm and herd management were good, the owner–operator enterprise being managed efficiently by a husband-and-wife team.
Faecal screens from severely scouring calves confirmed rotavirus as the cause. Despite evidence confirming adequate passive transfer (based on GGT concentrations in tested calves), the outbreak was severe and affected many groups of calves.
During the dry period, the farmers, vets and the MSD Animal Health technical team reviewed all the farm practices and facilities that could affect the prevalence of neonatal diarrhoea, looking to make realistic onfarm changes in 2015. They saw several possibilities for improvement:
1. Calf pens and group management
Simple, practical changes to the calf pens were recommended. These included use of solid partitions and an all in/all out policy, with calves remaining in set groups of similar age during their first three weeks of life. Once old enough, the calves from each pen were shifted across the road to a larger facility for the remainder of their rearing.
2. Hygiene
Bedding in the calf pens was replaced with clean wood shavings, a disinfection regime was established for the upcoming season and the disinfectant used was changed to a broad-spectrum product with antiviral properties.
3. Colostrum
Colostrum storage and utilisation were reviewed. First-milking colostrum was kept separate and used only for new-born calves for their first two feeds. The transitional milk from milkings two-eight was used for subsequent feeding of the calves. Tubing all neonates to ensure they got at least one colostrum feed, while still able to absorb crucial antibodies, became standard practice.
4. Calving pickups
Ideally pickups are done twice daily, but with no extra help over the busy calving period it was impossible on this farm. This placed calves at risk of not receiving the high-value colostrum from vaccinated dams shortly after birth.
Once-a-day pick up remained for most calves during peak calving – but tubing calves with colostrum (taken from vaccinated cows' first milking) in the paddock was adopted when pickup was not possible within 12 hours of calving. This provided the extra security that new-born calves could maximise their absorption of protective colostral antibodies shortly after birth.
Stored transition milk continued to be fed to calves in their first three weeks of life to maximise the protective properties of the antibodies.
5. Vaccination protocols
Split vaccination to cover the entire nine-week calving period was recommended to continue. The whole herd – including heifers, kept on the runoff – were vaccinated in 2015 with Rotavec Corona.
This was to ensure that as cows came into the milking herd all colostrum collected and fed to calves contained boosted antibody concentrations against the neonatal scour pathogens. This reduced the likelihood that poorly protected calves entering the calf pens would increase the risk of disease challenge to the other calves.
Following the interventions described above, the Forsyths had a much better calving season in 2015. Only two cases of calf scours were found, and neither was caused by rotavirus.
