Holly Ferguson knows her cow pies about as well as anyone. In the first study of flies in managed pastures in the Pacific Northwest, the entomologist has spent an unusual amount of time traveling the state and assessing its cow pies.

No matter the obvious jokes, dung dispersal in pastures is serious business. Wherever there are cows, there will be cow dung, and lots of it. A beef cow can produce nearly a ton of manure per month. And if that ton sits there untended, there will be problems.

WSU entomologist Holly Ferguson
WSU entomologist Holly Ferguson (Photo Robert Hubner)

Oddly enough, the conditions of the cow’s other major habitat, the feedlot, reduce the problem of dung dispersal, at least from one perspective. The constant crowded trampling of the feedlot cows eliminates the pasture’s particular dung problems.

Unattended cow pies in a pasture are a rich breeding ground for cow pests and parasites. Also, rather than fertilize the pasture as it would once it broke down, the inert dung is actually toxic to the pasture and stops grass from growing.

Fortunately, the cow pie in its natural state is generally, and eagerly, consumed by a wide number of insects, including the appropriately named dung beetle and any number of Diptera, or true fly, species. (Tidying pastures is such a priority that Texas, for one, imports dung beetles from Africa.)

And so, with various cohorts, Ferguson set out to address a widespread concern about the effect of parasiticides on the cow pie ecosystem.

If the researchers could come up with a solid recommendation regarding the use of parasiticides in pastured cattle, went the rationale, the logical outcome would be healthier pasture ecosystems.

Part of this story resides on a large cattle ranch in Hawaii. WSU entomologist Laura Corley Lavine is interested in dung fauna, the creatures that inhabit the pie, particularly beetles.

She is also interested in whether the dung beetles have any effect on pest species and has conducted research on the Kahua Ranch on the big island. Realizing the importance of cow dung dispersal, Tim Richards ’84 DVM, a family partner in the ranch, had observed the negative effect of parasiticides in the ranch’s cattle on the resident dung beetles and so had established a special formulation for the ranch’s cattle.

Hawaii has no native dung beetles, so it had imported them from Africa and Mexico.

Because of Richards’s care, says Corley Lavine, the Kahua Ranch has a “fabulous” population of beetles. “He has no manure in his pastures, the beetles get rid of it so quickly.”

However, says Corley Lavine, in Prosser, where Ferguson is stationed at the Irrigated Agriculture Research and Extension Center, they tried the formulation advocated by Richards and found no difference in the effect on beetle populations.

“Ranchers around here,” she says, “(if you) tell them you work on dung beetles, they say, ‘Oh we used to have great dung beetles, but now they’re all gone.’”

Unfortunately, there is no baseline study of beetle populations in the Intermountain West. Also, points out WSU entomologist Rich Zack, there never were many native dung beetles in the area. The more common ones are actually European.

Regardless of origin, and to make a long story short, the researchers were hoping for more conclusive advice regarding parasiticides. “We were hoping to say if you do this, you’ll have more beetles,” says Corley Lavine, which was the case in Hawaii and also in a North Carolina study. But here, in the Intermountain West, scientists could offer no recommendation, because of a surprising finding.

Work by graduate student Dan Skoczylas, who did his thesis on the effect of parasiticides on dung beetles, found no effect at all.

But what Ferguson did find in her survey of statewide pastures was another surprise—an incredible insect diversity in the cow pies. She and her fellow researchers decided to focus on Diptera as a diversity indicator. In her visits to 17 ranches in eight counties, both east side and west side, Ferguson found 47 dipteran families. Not species, but Family, the inclusive biological rank between Order and Genus. The only species identifications in the project were the pest species. And the rest? As they say in the business, more study is needed.

The pests to cattle are primarily face flies and horn flies. Adults of both species lay eggs on the fresh dung. Face flies can reduce weight gain in beef cattle and milk production in dairy cows. They are a vector, or carrier, for pinkeye, an eye infection that can lead to blindness.

The bloodfeeding by horn flies can irritate cattle to the point where they stop feeding, reducing weight gain and milk production.

Aside from some other, less noxious pests, says Ferguson, most of the dipteran species living off cow dung are beneficial, preying on the pests and also aiding in the degradation of the cow pie. That degradation is, in fact, a fine balance between maintaining adequate habitat for the beneficials and ensuring that the pies do not provide too good a habitat for the pests.

Interestingly, the study found greater diversity in pastures east of the Cascades. Although west-side pastures get more rainfall and would seem to encourage higher biodiversity, the habitat of east-side pastures is actually more varied. Not only do they contain the normal dry shrub-steppe, but they are often irrigated or have streams flowing through them, offering a broad habitat range.


On the web

Irrigated Agriculture Research and Extension Center (WSU Prosser)