Ear-tag retention and identification methods for extensively managed water buffalo (Bubalus bubalis) in Trinidad

Thirty-two young domestic water buffalo were studied to evaluate ear-tag retention during an epidemiologic field trial. Plastic ear-tags were placed in both ears before the start of the trial, which was implemented in an extensively managed domestic water buffalo herd of approximately 1000 animals in Trinidad from 1999-2001. The presence or absence of ear-tags was recorded at the times of animal handling. The rate of ear-tag loss was modeled using a parametric survival analysis assuming an exponential rate of loss. A gamma distribution was used to estimate the amount of time that each animal would be positively identified based only on the presence or absence of one or more ear-tags. The overall median ear-tag retention was 272 days. The estimated rate of ear-tag loss was 0.0024 ear-tags lost per day. The use of ear-tags alone might not be sufficient for long-term identification of extensively managed animal populations.