Cows in late pregnancy stages eating bark, berries and branches of western juniper trees are face a higher risk of aborting their calves or premature birth, Oregon State University researchers reveal.

The trees harmful impact on pregnant cattle was unknown until recently when a veterinarian in the eastern part of the state noticed a pattern of lost calves and sought OSU's help in resolving the reason.

"People had always wondered what happened to the 5-10%  of cows with lost pregnancies," says Tim Deboodt (cq), an OSU Extension range management specialist in Crook County. "So, we started our research from scratch on a tip."

A young juniper tree grows on an eastern Oregon ranch. Cattle can come into contact with juniper trees while grazing but have not desire to eat them if they have enough other food.

OSU researchers pinpointed the juniper for its labdane acid toxins, chemical compounds that construct the flow of air to a  fetus in livestock. In the early 1970s, the acids were identified in ponderosa  pine needles, and linked to premature livestock birth and pine needle abortion disorder.

Two of six heifers monitored by OSU scientists lost calves after eating parts of juniper trees during the final month of pregnancy. Only a small percentage of calves born early because of juniper or pine needle diseases are likely to survive without intensive veterinary care, notes Cory Parsons, a Baker County Extension livestock specialist.

"If cattle have plenty to eat, they have no desire to chew on juniper," he discovered. "When cows are hungry, they're going to fill their bellies up, especially during times of drought and heavy snow."

To reduce risk of exposure to juniper during the last trimester of livestock pregnancy, he recommends that ranchers slowly introduce the cattle to juniper areas if they have not been acclimated to the site. Cutting lower branches off of the trees is also advisable, as is providing adequate alternative feed on a daily basis to reduce the instinct to graze on juniper and other plants.