Evaluation of impacts of vaginal implant transmitter use in moose

Vaginal implant transmitters (VITs) are a popular tool in ungulate parturition studies and have been used in moose (Alces alces), but their potential impact on animal performance has not been thoroughly assessed. We looked at potential short-term impacts of VIT use on maternal condition through assessments of neonate calf mass, early calf survival, and parturition date. We also assessed long-term impacts of VIT use on future reproduction and the inflammatory response after prolonged VIT retention through qualifying discharge at VIT removal and measures of acute phase proteins haptoglobin and ceruloplasmin. We captured 54 neonates and assessed over 900 potential parturition events of 278 adult moose over multiple years and we did not detect any evidence of a negative impact of VIT use on neonate calf mass, parturition date, or future reproduction. We did find elevated haptoglobin and ceruloplasmin levels in non-pregnant individuals that had unintentional VIT retention past parturition, but this was not universal across all cases. We found a potential negative impact of VIT use on early calf survival which was likely driven by biased sampling. A bias can exist (i.e., left truncation) if sampling is mixed between cows that had a VIT (and, therefore, a known parturition time) and those without a VIT that were sampled opportunistically. Future evaluations need to overcome this bias when assessing early calf survival. With that caveat, we did not detect clear negative impacts of VIT use on moose and recommend late winter to early spring VIT insertion in pregnant females to minimize retention time.