Imagine 30% of your cowherd delivering premature calves, all within a 72-hour time frame. That nightmare was a reality in our herd of 200 cows last spring.

Abortions caused by Ponderosa pine needle consumption were higher than normal in southeast Wyoming last spring. In the southern Laramie mountain range, Ponderosa pine trees dominate the landscape.

Appreciated for protection against weather, the trees provide shelter from wind and moisture. But for pregnant cows, particularly ones in their last 90 days of gestation, they also pose a huge threat.

Cows consuming Ponderosa pine needles during their last trimester are quite susceptible to aborting their calves. Actually, abort is a misleading term since cows usually deliver live, premature calves.

Evidence suggests needle toxicity levels vary each year. Southeast Wyoming experienced a drought during summer 2000, as well as a colder than average fall and early winter. Whether or not these factors increased needle toxicity is scientifically unfounded.

However, since our cow management was the same as in previous years, an unknown variable was responsible for this drastic rise in pine needle abortions. I feel increased needle toxicity and colder temperatures both played an incriminating role.

Cows seem more attracted to needles during times of cold stress, regardless of how much feed and balanced mineral is available for consumption. It's been reported that cows must consume 3-5 lbs. of needles daily for several days before abortions occur. They can abort up to two weeks after being removed from a pine needle source.

Some theorize that isocupressic acid and vasoactive lipids — chemical compounds found in Ponderosa pine needles — cause decreased blood flow to the uterus. Stress signals the calf to trigger parturition.

Often the cow will not dilate properly, and the calf fails to fully enter the birth canal. Coupled with weak uterine contractions, the cervix can't expand since the calf's head will not push normally against the cervix.

In our experience, we would often see a cow with a tiny water bag, but no obvious signs of being in labor. If we waited to see if she would deliver on her own, the calf would die and we would have to take it out in pieces.

If we intervened and pulled the calf, we would find that the calf was still down below the pelvic brim. We would try to manually dilate the cervix and pull the calf into the birth canal. Although dilation would be incomplete, delivery of the calf was a necessity.

Upon delivery, premature calves were placed immediately into a warmed room and fed colostrum using a stomach tube. Often the cows didn't let down much milk, likely due to traumatic, premature parturition.

Colostrum mix was substituted in many cases. Antihistamines were also given to the newborns to help them breathe. The calves would eventually stand and nurse without much assistance, live a few days, but then a large majority would die.

Many of the surviving newborns seemed quite retarded for the first week, and special attention was paid to make sure they were actually consuming adequate milk. To measure actual consumption, cows were milked out and the calves were bottle-fed.

These young calves also were extremely susceptible to pneumonia. About 15% of premature calves did live to weaning age and were the same weight as their contemporaries in the fall.

In addition to causing premature parturition, retained placentas are another large problem associated with pine needle abortions. Peter Vorpahl, DVM, of Newcastle, WY, recommends administering a subcutaneous mega dose of penicillin to help treat uterine infection. Vorpahl also suggests allowing the cow to clean on her own without manual intervention.

Other veterinarians also advise the additional use of hormonal drugs such as lutalyse, oxytocin or estradiol cypionate (ECP) to help expedite membrane expulsion. However, the effectiveness of these drugs is unproven.

At the time of our wreck, I only gave an injectable tetracycline. Our breed-back rate in the fall was much lower than expected for cows that had aborted, with only 39% of these cows breeding back.

I attribute most of these fertility problems to cervical scar tissue formation due to forced extraction and uterine infections. Had I been more aggressive with antibiotic treatment, perhaps more cows would have cleared infection and conceived.

After this pine needle wreck, fencing to exclude trees from winter pasture and new windbreaks were built. No amount of feeding seemed to change cows attraction to needles.

In cows that must be exposed to Ponderosa pine trees during the last trimester of pregnancy, Black Hills, SD, cattle producer Steve Cullum has found that late afternoon or early evening feeding has helped. Cullum also advises providing supplements containing more energy than protein.

High levels of protein in a diet can result in mild ammonia toxicity. Condensed tannins, found in pine needles, lower ammonia levels in the bloodstream by binding with plant proteins. Binding prevents rumen microbes from converting the proteins to ammonia.

Cows on high-protein diets may seek out pine needles to lower ammonia levels. Therefore, avoiding high-protein diets may help to decrease pine needle consumption.

Hopefully, this article will inform others who may face a similar problem, as well as possible ways to decrease the problem. Ultimately, the best solution is to eliminate exposure to trees, but this may be infeasible for some ranchers.

Brenda Johnson co-manages the O-Slash-O ranch with owner Jim Willadsen. The 200-head cow/calf operation is located in Granite Canon, WY. She can be e-mailed at