COWS that eat the bark, berries or branches of western juniper trees late in pregnancy are more likely to abort their calves or give birth early, according to Oregon State University researchers.
The tree's harmful effect on pregnant cattle was unknown until an eastern Oregon veterinarian noticed a pattern of lost calves and asked the Oregon State University Extension Service about it.
"People had always wondered what happened to the 5-10% of cows with lost pregnancies," said Tim Deboodt, an extension range management specialist based in Crook County, Ore. "So, we started our research from scratch on a tip."
Oregon State researchers pinpointed that western juniper contains toxins known as labdane acids, which constrict the flow of oxygen to a fetus. In the early 1970s, labdane acids, specifically isocupressic acid, were identified in ponderosa pine needles, which also trigger premature birth in cows in a condition called pine needle abortion.
Two of the six heifers Oregon State researchers monitored lost calves after eating western juniper during the last 30 days of their pregnancies. Only a small percentage of calves born early because of juniper or pine needle consumption are likely to survive without intensive care, said Cory Parsons, an extension livestock specialist in Baker County, Ore.
Oregon State researchers are now conducting a larger study to examine juniper's effect on more than 20 cows in late pregnancy. Results are expected by this summer.
The researchers will also analyze if juniper consumption inhibits conception or bears any consequences early in pregnancy. Based on prior knowledge about pine needles, the researchers said they suspect that juniper is likely to cause cows to abort during the last trimester of gestation -- when fetuses need the most oxygen.
Oregon State's juniper research has been supported through a number of grants from the Oregon Beef Council and was published in a handful of academic journals, including Rangelands and the International Journal of Poisonous Plant Research.
Western juniper-caused calf abortions have not registered a large economic impact so far, Parsons said. Although some grazing cattle are in contact with juniper on a daily basis, cattle do not naturally seek it out as food.
In recent decades, juniper trees have been piled up as riprap to stabilize the banks of creeks and streams being restored in western states. Cows may come into contact with these trees when they use these watering holes.
"If cattle have plenty to eat, they have no desire to chew on juniper," Parsons said, cautioning, however, "When cows are hungry and bored, they're going to eat to fill up their bellies, especially during times of drought and heavy snow."
To reduce the risk of exposure to juniper during a cow's last trimester of pregnancy, Parsons recommended slowly introducing cattle to areas where juniper exists if they have not already been acclimated to the site. He also suggested cutting lower branches off of trees, if possible, and providing adequate feed daily to reduce the animals' desire to graze juniper.