Best Practice for Vaccination of Livestock - Includes an Overview of Leptospirosis in New Zealand (commissioned by the NZVA)
DAIRY ALERT: Has vaccination cleared Leptospira from dairy herds?
In 2010/11, vaccine efficacy in dairy herds with a history of vaccinating their stock regularly was investigated in an observational pilot study (Parramore et al., 2011). Ten cows were selected for urine sampling in each of 44 dairy herds. Herd managers were asked for timing, schedule, age, booster and regularity of vaccination, type of vaccine, herd size, whether the herd was open or closed, biosecurity measures, previous leptospirosis history, and other animal species on farm. Urine samples were tested by dark-field microscopy (live Leptospira) and Real Time-PCR (live Leptospira or DNA) and shedding was defined as being positive to either test.
No serological data were available from the sampled animals, information about vaccination inquired from farmers appeared somewhat uncertain, and tests employed may not be 100% accurate. Therefore, the results are preliminary and require confirmation at this stage.
There was evidence of shedding in 30% of the herds and 13% in animals from positive herds (Table 2). Because animal prevalence was low and only 10 cows were sampled per herd, a number of herds might have been misclassified as ‘not-shedding’. Thus, the true percentage of herds harbouring shedders may well be higher, despite a long standing history of vaccination. On the other hand, PCR may detect small amounts of DNA from live or dead leptospira, thus the DNA-presence per-se may not have indicated that exposure reached an infective dose.
Dairy herds and cows shedding leptospira testing 10 selected cows per herd
Age at first vaccination was the only significant factor associated with the probability of shedding. The results suggest that Leptospira challenge of calves at an early age still exists on dairy farms using vaccines, for example through heifers returning from a contaminated rearing property. Vaccinating already infected animals may not be effective, as it is known that vaccination after natural challenge reduces vaccine efficacy. Neither vaccine type nor the number of serovars included (2 vs 3) altered the shedding probability.
Risk of one or more shedders in the herd relative to age of calves at first vaccination