DOI: 10.25338/b89d1s
title: Natural causes of white-tailed deer morbidity and mortality in New York State

description: White-tailed deer Odocoileus virginianus are the most
 popular big game animal in the United States. Recreational harvest of
 these animals is a critical tool in population management, as well as an
 important financial resource for state economies and wildlife agencies.
 Thus, herd health evaluations can provide information to wildlife managers
 tasked with developing sustainable harvest practices while monitoring for
 emergent problems. The purpose of our study was to document causes of
 illness and natural mortality in New York white-tailed deer submitted for
 post mortem evaluation. Animals were presented by members of the public
 and wildlife management personnel due to abnormal behavior or unexplained
 death. We describe demographic and seasonal associations among gross and
 histologic evaluation and diagnostic testing. Post mortem examinations
 were performed on 735 white-tailed deer submitted for necropsy in New York
 from January 2011 to November 2017. Causes of euthanasia or mortality were
 classified into nine categories. The most common findings were bacterial
 infections, trauma not evident at time of collection, and nutritional
 issues, primarily starvation. Using a multinomial logistic regression
 model, we looked for associations between the mortality categories and
 age, sex and season. Compared to the baseline of bacterial deaths, adults
 were less likely to have died from nutritional and parasitic causes, males
 were less likely to have died from other causes, and risk of death from
 nutritional reasons decreased from season to season, with lowest risk in
 winter. These methods can help wildlife biologists track changes in
 disease dynamics over time.
description: Two of the highest priorities, also reflected in the New York
 State Interagency CWD Risk Minimization Plan, are to detect chronic
 wasting disease (CWD) in the deer population and document causes of death
 and disease in white-tailed deer. Standardized criteria for submission in
 the surveillance program are: 1) live deer behaving abnormally or in poor
 body condition necessitating humane euthanasia and; 2) deer found dead
 without an obvious cause of death or found to have some abnormality. DEC
 may be notified of deer meeting these criteria by members of the public or
 law enforcement and can submit the animal for necropsy and diagnostic
 testing. Because the surveillance program specifically excludes deer that
 died from obvious predation, hunting, and deer-vehicle collisions, animals
 collected do not represent the New York population as a whole; however,
 they are valuable for assessing the breadth of diseases affecting wild
 deer and establishing a standardized baseline for future assessment. A
 benefit of this program is that these animals can serve as sentinels for
 emerging diseases. This type of opportunistic surveillance is a widely
 used method for states to prioritize deer that could be infected by CWD
 (Joly et al. 2009). Providing a basis for comparison will allow states to
 refine their surveillance systems to be better informed about white-tailed
 deer diseases by demo- graphic categories and seasonality.
 For the present study, records from deer presented for necropsy
 through the surveillance program from 2011 to 2017 were compiled to
 retrospectively evaluate disease occurrence in a subset of the New York
 deer population. A total of 534 deer out of 735 that died between January
 2011 to November 2017 met the criteria for inclusion in the study. Deer
 that died from obvious, non-natural causes, including deer killed for
 diagnostic tests (9), forensic studies (102), research (21), hunter killed
 (49), obvious vehicular trauma and predation (20) were excluded. The study
 population consisted of 230 females, 169 males, and 135 animals of unknown
 sex. There were 227 adults, 157 juveniles, 17 neonates, and 133 deer of
 unknown age. Weight data was available for 215 cases in which full
 carcasses were submitted.
description: Please see github repository for data as well as R
 code: https://github.com/sophiemzhu/deer. The majority
 of the animals for which sex (missing=U), age (missing=0) and weight
 (missing=NA) data were unavailable were in the “unknown” cause of death
 category (n=253). Of these, a diagnosis could not be obtained in 168
 because of insufficient data histories and lack of appropriate tissue
 collection. Missing data in the remaining cases was due either to missing
 tissues, autolysis or failure of the prosector to record the
 data.