You are here

Update

Update header image
Oregon State University Agricultural Research updates

Researchers Studying Male-Oriented Rams

Scientists studying male-oriented mating behavior in some rams have found links between sexual preference and chemical activity in the brain.

A report on the work, co-authored by OSU animal scientist Fred Stormshak, was published in Biology of Reproduction, a scientific journal.

Stormshak and scientists from several other institutions investigated the sexual behavior of adult male sheep that prefer to copulate with males rather than females.

"This is a costly problem for sheep producers because breeding rams are worth $300 to $500 each," said Stormshak. "Outwardly, there is no way to tell whether a ram is male-oriented, so the producer runs the costly risk of buying an animal that will never produce any offspring."

Sheep producers lose thousands of dollars yearly from the purchase of breeding rams that turn out to be male-oriented, Stormshak added. About 8 to 10 percent of all rams are male-oriented, he said.

The researchers focused on the part of the brain called the hypothalamus, a center for the formation of reproductive behaviors in most mammals.

"We concentrated on aromatase activity in the hypothalamus," said Stormshak. "Aromatase is an enzyme that converts testosterone into estrogen in the male."

In some species, he noted, the hormone estrogen brings about mating behavior in which males seek females for copulation. These data reflect the biology of sheep and are "not construed to be applicable across species," Stormshak pointed out.

After reaching 16­18 months of age, the rams in the study were given sexual behavior tests to determine their preference for either females or males.

"We found that in regard to mating behavior, the rams fell into three categories," Stormshak said. "One group mated with females again and again, a second group mated with females occasionally, and the third group did not mate with females at all."

Following further mating preference tests, tissue and blood samples were collected from selected rams. Analysis of those materials led to the general conclusions that male-oriented rams convert less testosterone to estrogen in the hypothalamus component of their brains, and that these rams have reduced capacity for production of testosterone, compared to female-oriented rams.

"These results raise the question of why the testes of some rams produce less testosterone than others," Stormshak said. "Unfortunately, there is no answer for that question now."

Stormshak and colleagues are following up with a project that will analyze the possibility of altering the male-oriented behavior of rams with an estrogen implant.

The initial research team included John Resko, Charles Roselli and Jerome Choate of the Oregon Health Sciences University, and Anne Perkins of Carroll College in Helena, Montana.

Borrowing May Help Livestock Industry

By borrowing a strategy from Down Under, Pacific Northwest ranchers are going to be able to save on selenium treatments for their livestock, OSU researchers believe.

The strategy calls for applying selenium to pastures instead of giving selenium injections to cattle.

"Injections or oral treatments of selenium cost $3 to $10 per head. Applying selenium with fertilizer would cost about 33 cents a head," said Randy Dovel, a research agronomist at OSU's Klamath Experiment Station.

Dovel said the selenium formulation he uses is sold commercially in Australia and New Zealand. Like the Pacific Northwest, those countries have selenium-deficient soils that produce selenium-deficient forage.

Selenium deficiency causes white muscle disease of cattle and sheep, which affects animal reproduction, weight gain and general health.

Studies by Dovel and Ron Hathaway, a Klamath County extension livestock agent, showed that about one-half ounce of selenium per acre applied to the soil is enough to produce forage without deficiency.

"We found that just one pound per acre of the commercial material is all we need," Dovel said. "We mix it with a nitrogen-based fertilizer and apply it at the same time we fertilize."

Insects Can Help Us Manage The Forests

It took decades to give Smokey the Bear a decent burial and bring fire back into the forest ecosystem. It might take even longer to enhance the image of bugs, experts say.

Even in an age of enlightened forest management, it's tough to find the word "insect" used without "pest" attached. But new studies at OSU have concluded that a variety of insects can play major roles in forest ecology-many positive.

Men walking in a forest with downed trees.

OSU scientists examine a forest altered by the spruce budworm. Photo: OSU's Extension and Experiment Station Communications

"Research has already shown that insects are a key in cycling nutrients, speeding decomposition and building soil fertility," said Tim Schowalter, an OSU Agricultural Experiment Station entomologist. "It now appears they do far more than that.

"In Oregon we've viewed the major insect epidemics as disasters," Schowalter said. "Those destructive outbreaks are having an effect that's roughly comparable to fire. In some ways they're doing the forest underthinning that fire would have done and we should have done."

If nothing else, the insects are a clear indicator of forest health, according to Schowalter.

"What they're telling us is that fire exclusion allowed a huge invasion of understory shrub and tree species that don't belong there," he said.

The insects have already taken the liberty of killing many of those plant species, he added. Now, if catastrophic fires don't first burn everything up, the insects may help create openings in the forest, improve water availability and give a major nutrient pulse to surviving trees.

In other words, they could work in concert with fire to restore forest health to eastern Oregon. Some areas, Schowalter said, are already healthier than they have been in half a century.

In pioneering research, much of it done at the H.J. Andrews Experimental Forest near Blue River, OSU scientists have learned about roles insects play in forest ecosystem processes.

Defoliating and sap-sucking insects affect nutrient turnover. Wood-boring insects penetrate bark and provide access for decomposers and water, accelerating decomposition. Insect outbreaks can open holes in the forest canopy. Trees that survive get a burst of nutrients that improves their growth and health.

In a normal forest ecosystem with a diversity of insects and the natural presence of fire, Schowalter said, tree species that are appropriate for that terrain grow and thrive. Inappropriate species are weeded out. If drought or wet cycles tend to push the ecosystem out of its usual balance, fires and insect attacks help bring it back.

At this point, Schowalter said, concessions may have to be made to decades of fire exclusion and insect suppression. As a member of Governor Kitzhaber's task force to study eastern Oregon forests, he agreed with recommendations for low-elevation salvage logging and more use of controlled fire to improve forest health.

Nursery Disease Harder To Control

A disease that causes problems for Oregon's $400 million-a-year-plus nursery industry has developed resistance to both the chemicals used to control it, an OSU study shows.

Pseudomonas syringae bacteria, which cause a disease commonly known as bacterial blight, are already responsible for more than $8 million in annual losses to the nursery industry.

As chemical resistance spreads it's believed the problem will worsen. A survey of 44 Willamette Valley nurseries showed the bacteria at all the nurseries, with 467 strains isolated from 25 plant species.

Woman looking closely at a lilac plant.

OSU graduate student Heather Scheck eyes a lilac plant damaged by bacterial blight. Photo: Lynn Ketchum

The bacterium "produces a toxin that kills flowers and new growth, and causes cankers on more than 160 green and woody plants," said Heather Scheck, a doctoral candidate in OSU's Department of Botany and Plant Pathology.

In recent years growers have complained that the chemicals they use most often to control bacterial blight-copper and streptomycin-seem to be losing their effectiveness. And the disease often makes plants appear at their worst during spring, the prime sales season.

"We discovered that different phenotypes of Pseudomonas syringae have rapidly evolved in the past 10 years with resistance to either copper, streptomycin or both," said Scheck, who works with OSU Extension plant pathologist Jay Pscheidt.

The OSU researchers have found some approaches that help address this problem.

Studies show that streptomycin resistance means the bacteria is virtually invulnerable to that chemical. But it appears that copper formulations with a higher concentration of "free ions," in a wettable powder form, still provide some control.

Brand names of chemical products that meet that criteria and are available in most garden stores include Microcop, C-O-C-S, and Kocide 101 in its wettable powder form.

Other non-chemical measures that can help include allowing more space between plants and pruning to maintain air flow within the canopy. Cover from rain is also very helpful, and growth of more plants either under cover or in greenhouses may be one solution available to the nursery industry.

Continued research at OSU will work to find other types of treatments that can address this problem, Scheck said. So far, there has been little success in finding genetic resistance among plant species susceptible to the bacteria, she added.