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Grazing with White-tailed Deer: Simple Solutions for Complex Problems

Rachel White

Summary

“Grazing with White-tailed Deer: Simple Solutions for Complex Problems”

Rachel White1, Tuuli Overturf1,2, Ann Bryant1 and Anne Lichtenwalner DVM PhD1,2,3
1University of Maine School of Food and Agriculture/Animal and Veterinary Sciences, 2UM Honors College, 3UM Cooperative Extension
Contact email: Rachel.whitney@maine.edu

Abstract:

White-tailed deer (Odocoileus virginianus; WTD) can introduce problems for farmers that increase risk of production loss. Specifically, transmission of a zoonotic parasite, meningeal worm (Parelaphostrongylus tenuis; P.tenuis) can cause severe neurologic disease or death in livestock, primarily small ruminants (sheep, goats, llamas and alpacas). Small-scale farmers face a large risk of production loss due to meningeal worm, as even a small increase in mortality can have a large financial impact.

Farms where livestock grazing systems overlap with WTD habitat (P. tenuis definitive host) and that harbor high numbers of terrestrial gastropods (snails and slugs; P. tenuis intermediate hosts) face elevated risk of meningeal worm infection. Livestock are considered “dead-end” hosts for the parasites which are unable to complete their reproduction cycle. P. tenuis migration in livestock causes neurological signs, such as ataxia, hind-end paralysis, head tilt, circling, and (usually) death. Currently, there is no definitive diagnostic tool for this parasite except for necropsy, but careful behavioral observation may detect early neurologic defects. In affected livestock, larvicidal treatments can be utilized effectively if neurologic symptoms are caught early. However, the best approach to reducing loss due to meningeal worm is to exposure by using preventive management.

Farms with WTD presence in arid regions do not have as high of a risk of P. tenuis exposure because the environment does not support terrestrial gastropods as effectively as do wetter, cooler climates.. In the eastern US, P.tenuis infection has been seen in horses, sheep, goats, llamas, alpacas, and cervids. Several preventive measures can be utilized to avoid increased risk of meningeal worm infection and fatalities.
1. Assess the risk of P. tenuis on farms by running gastropod surveys and inspections for larval infection.
2. Reduce the chances of gastropod ingestion by farmed animals using natural/organic or chemical treatment of pastures.
3. Reduce or eliminate grazing periods on wet pastures or during wet, cool periods that are ideal for terrestrial gastropod activity.
4. Use controlled harvesting of WTD on high-risk farms to reduce the spread of P. tenuis to gastropods.
Small farmers may reduce costs associated with meningeal worm-related illness or deaths to their livestock by implementing effective preventive means, and by early diagnosis via careful observation of livestock behavior.

This project will estimate risk of P. tenuis infection to sheep in overlapping grazing systems with WTD. Gastropods and WTD fecal pellets were collected from two different farms in Maine and examined for P. tenuis larvae. 81% of deer pellets (n=16) and about 4% of snails (n=491) carried P. tenuis. The study will continue with a survey for Maine sheep farmers about their pasture systems and if they have had P. tenuis related symptoms or deaths. Deer fecal pellets and gastropods will be collected on these sheep farms to determine meningeal worm prevalence. Domestic ducks will also be assessed for effectiveness as a means of gastropod removal. Producer education about behavioral assessment will be developed to aid early detection, and to direct producers to seek appropriate veterinary treatment.

Keywords: Meningeal Worm; Zoonotic; Production loss; Pasture Grazing Systems

Details

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