PROVIDING only a single shot 5-in-1 vaccine to calves at the time of castration or dehorning may not be effective in preventing mortality, research conducted in northern beef herds indicates.
Vaccination against common clostridial diseases in cattle is recommended as best practice husbandry. However, except for botulism, the practice of vaccinating cattle for clostridial diseases is not undertaken by a significant proportion of the northern beef cattle industry in extensive management systems.
In a recently-completed Northern Territory pastoral industry survey, only 8 and 13 per cent of respondents in the Barkly and Katherine regions, respectively, administered at least one vaccination of either 5-in-1 or 7-in-1 vaccine to weaner cattle.
Low adoption is partly due to the logistical constraints of administering booster vaccinations four to six weeks after the first vaccination, as per the manufacturer's recommendation.
It means significant proportions of young cattle are are potentially at risk of infection by clostridial disease, such as tetanus, and production loss when husbandry procedures are performed, according to livestock scientist with the NT Department of Primary Industry and Resources Kieren McCosker.
The latest research, funded under the Meat & Livestock Australia producer demonstration study program with co-investment by NTDPIR and Zoetis, investigated the effectiveness of only providing a single shot of 5 -in-1 vaccine at the time of husbandry procedures under field conditions.
Development of immunity to most bacterial vaccines is thought to occur within 10 to 14 days and also approximately coincides with a potential challenge by clostridial diseases like tetanus or gas gangrene, meaning that an initial shot followed by a natural challenge may have offered some protection, Dr McCosker said.
The research also documented mortality rates in recently-weaned cattle managed under commercial conditions.
The study
A dozen cohorts of calves across 10 Northern Territory stations were allocated to either a 5-in-1 vaccination or control treatment group at the time of castration or dehorning and were then monitored for four months on average, some up to 10 months.
The percentage of animals missing at future musters was compared and was considered an indicator of suspected mortality.
The vaccination group were injected subcutaneously with 2ml of Ultravac 5-in-1 vaccine, while the control group were not vaccinated at all. All husbandry procedures were completed by station staff, including the administration of vaccinations.
Results
On average, 6.6pc of all study mobs were identified as missing. This greatly varied between stations, ranging from between 2.7 and 15.5%.
"The timing of mustering was thought to partly explain this variation with those stations that conducted re-mustering sooner, generally observed as having a lower prevalence of missingness," Dr McCosker said.
However, it was noted 'missingness' is an overinflated estimate of mortality as some 'missing' animals were likely to be alive but failed to be located and mustered, Dr McCosker said.
Approximately 66 per cent of animals that were 'absent' at the first muster were possibly mismustered, as they reappeared at the second muster.
Unfortunately, some stations were not able to complete two musters. However, had a second subsequent muster been completed on all stations, and assuming similar levels of miss-mustering across stations has occurred, the potential estimate of overall missingness is 4.1pc, according to Dr McCosker.
No link
The analyses showed that there was no association between vaccination status and missingness within both males and females. Similarly, there was no association between vaccination status and missingness when analyses were repeated for each of three subsets of data restricted to only those animals that had been castrated, dehorned or having exposed frontal sinus.
Dr McCosker said the results appear to suggest that only providing a single shot of 5-in-1 vaccine at the time of performing husbandry procedures does not provide a preventative level of immunity against infection by clostridial diseases.
"Potentially, the lack of response could be due to the prevalence of exposure being very low and the number of animals involved in the study were insufficient to detect differences," he said.
"It is also unclear if the administration of two shots four to six weeks apart, as per manufacturer's recommendations, or a single shot a fortnight prior to procedures would have produced a different outcome.
"Vaccinating animals four to six weeks apart has been demonstrated to provide a preventative level of immunity but it requires additional mustering and handling of animals, which is expensive and also often difficult to adopt in extensively managed herds.
"However, progeny are regularly separated from breeder management groups and stock piled in cattle yards prior to husbandry procedures being conducted approximately one to two weeks later as a part of the weaning process.
"Vaccinating animals at the time of separating from breeders and again at the time of conducting the husbandry procedures at least 14 days later is potentially an improvement to just providing a single vaccination and that could be practically implemented. It requires further investigation."
Employing good surgical technique, ensuring adequate drainage of the surgical site and by appropriate disinfection of the surgical site and instruments was also likely to avoid many cases of tetanus when open castration is used, Dr McCosker advised.