MILES CITY, Mont. - Growing up, Tim Donnelly saw how bad it could get when a rancher's cows consumed too many pine needles. In one particular year, one in 10 cows on the ranch where he worked aborted their calves.
Donnelly, who now owns that ranch, doesn't want to see that happen with his herd. He's cut down thousands of pine trees in winter pastures, leaving behind junipers and ash trees.
''We've resorted to, 'If we're going to live here, we've got to clear-cut certain pastures to make winter pastures of them,''' said Donnelly, a Miles City-area rancher who typically runs 300 cow-calf pairs and dozens of yearlings.
Needles from certain pines, such as ponderosa, contain a resin acid that causes cattle to abort. The so-called ''pine needle abortions'' are estimated to cost ranchers millions of dollars in calving losses annually.
''Usually a guy with 200 cows may lose two to five (calves) a year,'' said Jim Pfister, a rangeland scientist at a U.S. Agriculture Department poisonous plant research lab in Logan, Utah. ''That costs a lot, in terms of the checkbook, but it's not going to make the local newspaper.''
The trick is how to keep cattle from eating pine needles when the pasture may be loaded with them.
''Pine needles are not highly nutritious feed. They're loaded with resin acids and have to be a little distasteful,'' said Kip Panter, research animal scientist at the Logan lab.
Still, some cows apparently like the needles. Panter noted that needles comprise 20-30 percent of some cows' diets on any given day. That is worrisome because even a small amount of needles can induce abortion.
Researchers haven't quite figured out yet why some cattle have a fondness for pine needles while others don't. They know the tendency to eat needles rises in the winter, when snow on the ground covers forage and extreme cold stresses cows.
Pfister said studies conducted during recent relatively warm winters in Oregon, Montana and South Dakota found that cows avoided eating the needles. During cold snaps, pine needles have comprised as much as half a cow's diet, Pfister said.
Some Western ranchers like Donnelly have restored to clearing grazing land of ponderosas, to eliminate threat. Others, like southwest South Dakota rancher Ned Westphal, change their feeding programs to help discourage grazing on needles.
A return to a more normal winter could cause a resurgence of pine needle abortions, Pfister said.
Pine needle abortion occurs primarily in the western parts of Canada and the United States, Pfister said. Problem areas include the Black Hills of South Dakota, northeast Wyoming, eastern Montana, parts of Arizona and New Mexico and parts of Oregon and Washington.
''In Montana, or anywhere with pine trees, if cows are in late pregnancy during the winter, there is fairly high risk that they'll abort,'' said Robert Short, a USDA research physiologist.
Short, who has studied the problem for about 15 years, said animals such as elk, bighorn sheep, mule deer and whitetail deer can eat pine needles in late pregnancy with no ill effect. Differences in digestion could be one factor, he said.
Researchers have tried to find ways to keep cows from eating pine needles and to prevent the effects on cows once they have.
''We've tried dozens of tricks and treatments but have come up blank,'' Short said.
He advises ranchers to take cows out of grazing pastures with pine trees, but acknowledges ''that's a severe restriction for some ranchers.''
Westphal, a Custer, S.D.-area rancher who first encountered the problem decades ago, has sought several solutions over the years: locking up the cows, clear-cutting pastures and changing feeding patterns. The latter, he says, has worked the best.
He now feeds in the afternoon, so his cows are full when they bed down at night. At daylight, they head to ''lick barrels,'' a block of dehydrated molasses that includes vitamins and minerals.
He hasn't had problems with pine needle abortion for the past few years.
''When we first came here, some guys told me that it was part of living in the trees. I said, 'Wait. That's not a feasible, reasonable way to run an operation.'
''There isn't something you can put your finger on and say, 'This is it,''' he said. ''But you have to manage your operation around it.''