Vaccination in practice
Case study 1 - Victoria River district (NT) vibriosis trial
A trial was conducted in 2004-05 and 2005-06 to determine whether there was any economic benefit from giving maiden heifers one injection of a vibriosis vaccine (Vibrovax™) just prior to joining. The vaccine instructions stated that heifers older than 18 months of age only require one injection of the vaccine to gain immunity from vibriosis for two years.
Since most heifers are joined for the first time at two years of age in the Northern Territory, giving one injection of a vaccine is a practical treatment, whereas a vaccine that requires two injections several weeks apart is not practical, due to the high mustering costs associated with large paddocks.
The vaccinated group (VIB) and the control group (CON) all grazed together in the same paddock and bulls (mixed ages) were introduced to the heifers in late December and remained with them continuously from that point onwards. Several fences were washed down over the wet season and as a result, other bulls gained access to the paddocks – in addition, not all heifers were re-mustered. In both years of the trial, at the round one muster, pregnancy rates in the vaccinated group (VIB) were 11% higher than in the control group (CON).
Note: the presence and severity of diseases vary markedly between years depending on seasonal conditions, feed supply and vector spread (disease spread by insects), so never rely on the results from just one year. Understand all the factors that determine disease outbreaks.
Case study 2 - Pilbara botulism trial
A trial was established to assess the effectiveness of vaccinating for the toxin Botulism. In September 2006, two thirds of the trial heifers were vaccinated with Pfizer Longrange™, with the other third remaining unvaccinated as a control. Trial animals were identified with RFID (radio-frequency identification) tags and were flagged on the computer system linked to a tag reader. The vaccinated group of animals were re-vaccinated at the second round of mustering in September or October over the next three years.
Due to the extensive nature of the station and the large number of cattle, it was impossible to confirm the death of many of the trial animals. Instead, the measure of the effectiveness of the vaccine was the presence or absence of animals for more than three consecutive musters, with animals missing three or more musters considered to have died.
After the first two years, some heifers were dispersed throughout the breeding herd and the computer system allowed these animals to be tracked. The computer recorded the last date that an animal’s tag was scanned, and therefore it could be determined how many mustering rounds an animal had missed. It is conceivable that animals may have been ‘missing’ for several years then reappear.
Both vaccinated and control animals had the same opportunities to disappear and then reappear. However, there is also a high probability that the majority died. Animals were not confirmed dead unless the carcass was sighted, and the RFID tag recovered. Results indicated that 7% fewer animals from the botulism vaccinated group were missing for three or more musters compared with the unvaccinated control group.