The needles of ponderosa pine cause abortion when grazed by cattle. Induced abortions generally occur in late fall to early spring, during the last trimester of pregnancy. Cattle generally graze pine needles during storms with increased snow, wind, cold, changes in feed, or hunger. The toxin that causes abortion is isocupressic acid.

The ponderosa pine is a hardy tree that is used extensively as timber. Both the dry and green needles from the ponderosa pine tree can cause abortion in cows.
 

Where and When It Grows
Ponderosa pine grows in all of the states west of the Great Plains and in western Canada. Pine needles can be made available to cattle from slash remaining after logging operations, windfalls, or dried fallen needles. Discarded Christmas trees have been known to cause abortions in cows. Lodgepole pine (P. contorta), common juniper (Juniperus communis), and Monterey cypress (Cupressus macrocarpa) also contain isocupressic acid and may also cause abortions when eaten by cattle.

How It Affects Livestock
Abortions generally occur between 48 hours and 2 weeks after exposure to pine needles. The abortifacient dose is highly variable as some cows are highly sensitive and a small amount of needles will induce an abortion. Abortion incidence can vary from only a few to 100 percent of the cows involved. In observed field cases of poisoning, the cows appear to have no other signs of intoxication other than abortion and its sequelae. Experimental studies have found some animals develop rumen atony, indigestion and at high doses some may develop renal and neurologic disease. The aborted calves may survive if the abortion occurs in late gestation; however, they are small and weak, may not suckle, and generally require extensive care and treatment to survive. Nearly all the cows that abort develop persistently retained placenta and subsequent endometritis. These animals generally require treatment.

Signs and Lesions of Poisoning