Ponderosa Pine needle poisoning is really a thing.
I found this out to my cost the first year of keeping
cattle on my farm in Idaho. The Pacific Northwest is predominantly conifer forests, thus very different from the deciduous forest of my
native Missouri. If you search on the internet, this comes up "Ponderosa pine needles cause abortion and a poorly described toxicosis when eaten by cattle. In previous trials, the abortifacient compound of pine needles was identified as isocupressic acid. At abortifacient doses, isocupressic acid caused no other toxicosis."
Once you start following the threads there is lots of scientific papers available - but it is very easy to get into problems because 'the locals' all know better than to run pregnant cows in Ponderosa Pine stands - but don't necessarily think to pass on that knowledge.
My
experience happened the first year of keeping pregnant cows on this farm. In the spring 4 out of 5 cows aborted some weeks before their due date and the one cow that hung onto her pregnancy produced a weedy baby that never really thrived and cost more to
feed to butcher age than the volume of meat produced. Our farm is mixed timber and pasture, but most of the paddocks include at least a patch of woodland for
shelter. The north side of the property is mostly Cedar, Hemlock and various firs, that appreciate a bit of moisture. The south facing slopes, however, are much drier and populated mostly by Douglas Fir and Ponderosa Pine. On the north facing slopes we have now removed every Ponderosa Pine and stay watchful for new seedlings, but on the south facing side of the property, that would be impossible. Hence we do not use any of the paddocks on the south side for cows in their third trimester of pregnancy.
One of my friends that works in the cattle industry related a story from around 20 years ago that is cautionary. They were looking after a large herd of about 300 cows and one winter evening got stuck overnight in Spokane during a heavy snow storm. When they got back to the ranch they found that a large Ponderosa Pine tree that was in woodland adjacent to the field the cows were in, had been brought down by the wind/snow and had fallen across the
fence so the top of the tree was in the cow's field. When they finally got home, the needles had been stripped from a lot of the branches and there were nearly 100 aborted fetuses in the field. That represents a financial disaster for a rancher.
I was puzzled by these two events (mine and hers). Why would cows seek out a plant that would have harmful consequences - usually, unless in starvation conditions, most animals have the sense to avoid toxic plants. I found
the answer in a published paper. Apparently this particular tree, when subjected to sub-freezing weather, produces a substance in its needles that acts as an antifreeze. Many people have lost dogs and cats to carelessly handled car antifreeze because it tastes sweet. The Ponderosa Pine needles are the same - freeze them, and they produce a sweet tasting antifreeze that causes abortion in ruminants (
deer and elk as well). In the dead of winter, green sweet tasting vegetation must be quite attractive to cows.
I've written this as a new topic so the warning doesn't get lost in other threads.