I’m starting a new project for my post-doc, and decided that it would be fun to blog about it in addition to my standard repertoire. This is probably the craziest, most complicated project I’ve ever attempted.
Our story starts with goats and invasive plants. Goat browsing is being used more and more to combat invasive plants, particularly in the Midwestern US where I am located. However, actual data are scarce describing the long-term effects of goat browsing on both invasive plant populations and native plant community composition. The goats definitely strip the leaves from invasive shrubs, but we don’t know how much this damage affects population growth. Something else to consider is the fact that goats themselves are invasive species on a number of islands, where they are a serious threat to native plants. It is important to monitor the effect that the goats have not only on the invasive plants but also the effect on the native plants to make sure that we understand any non-target effects of goat browsing. All invasive plant management techniques have non-target effects, but it is important to know what they are so that they can be mitigated.
There is another issue with using goats to manage unwanted vegetation. When goats browse in temporary pastures (in or out of the woods), they come into contact with a potentially fatal parasite (Parelaphostrongylus tenuis aka brainworm or meningeal worm). The usual host of this parasite is white-tailed deer. In the normal course of events the parasites hangs out in the meningeal tissues of the deer, gets it on, and reproduces. The parasite doesn’t cause the deer many problems except in extreme cases, so a large percentage of deer carry the parasite (~40%). However, in other hosts (like goats, sheep, moose, and alpaca) the parasite can get confused. Rather than hanging out in the meningeal tissue, which would be better for everyone, the parasites go walk-about into the brain and spinal cord. The parasites never reproduce, and the incidental host suffers neurological damage. Mild cases might involve a limp. Severe cases can lead to paralysis, lack of interest in important activities like eating, and death.
Like other parasites, meningeal worm has a complicated life cycle. The parasite requires an intermediate host to complete its life cycle. A goat can’t become infected by coming in contact with deer poop (which contains the first stage larvae). A goat can only be infected with the parasite if it eats a snail or slug intermediate host carrying third stage larvae. This sounds improbable at first glance. Why would an herbivorous goat eat a snail? However, most terrestrial snails are extremely small (some only 1mm long). It would be very easy for a goat to accidentally eat many of them during normal leaf-stripping activities.
So, is there anything we could do to try to reduce the exposure of the goats to this horrible parasite? Maybe. My spouse and I had an idea when we met a goat that had contracted meningeal worm when we were living in Ithaca, NY several years ago. We suggested that the goat’s owner could try co-pasturing her goats with geese or ducks. Since geese and ducks eat snails and slugs, they may be able to interrupt the life cycle of the parasite. Fewer infected snails should mean fewer infected goats. We are going to try co-grazing the invasive plant management goats with geese and ducks to experimentally test whether this practice might reduce the exposure of the goats to the parasite.
That’s all for now, but expect some updates as the field season progresses. In closing, I’d like to thank some people who have made this project possible: the Minnesota Invasive Terrestrial Plant and Pest Center (MITPPC) for funding the project, Tiffany Wolf and Dan Larkin for throwing their academic weight behind the project, and Jake Langeslag from Goat Dispatch, who is our industrial partner and chief goat wrangler.