My cows and goats will wipe out baby pine trees and kill grown trees by stripping the bark down to the fleshy part of the trunk. They have mineral blocks. Why does livestock eat pine trees?
Livestock (in this case referring to cattle) usually don't eat
pine trees, particularly if they have all the nutritional
requirements of their diet met. In this case, it doesn't sound like
a particular nutrient has been met, hence their need or want to
strip bark off of trees or, if you have wood fences, chew on the
wood boards. This particular mineral is Phosphorus, and is usually
not found in most mineral blocks purchased at your local farm
store. Most mineral blocks are "trace mineral" blocks, which means
they have 95% salt and 5% micro-minerals consisting of elements
like copper, iron, iodide, cobalt, molybdenum, magnesium,
manganese, and sometimes selenium if they're advertised or labelled
as selenium blocks. Phosphorus is a macro-mineral, along with
calcium, nitrogen, potassium and sodium.
Without knowing what sort of "diet" your cattle are on, (though
I assume it is grass-fed with no grain, from the sounds of what
they have access to), it is hard to pin-point or let you know what
exactly can be done to curb the problem of your animals consuming
and killing your trees. However, what can be suggested is to add in
another supplement that has phosphorus in it, such as loose
mineral, or find a mineral block that has higher levels of
phosphorus than the one you have always been feeding. I mentioned
before how TM (trace mineral blocks) are not enough to satisfy your
animals' needs, but that isn't exactly truthful because cattle
actually need a lot more salt than minerals, even though some
producers claim that cattle will lick and lick away at the block
and not get much from it except a lot of salt. You can still opt to
feed them the TM block and add some sort of supplement that is high
in phosphorus (such as grain), or you can switch your mineral
program and feed loose mineral with salt in it. Depending on the
mix of the loose mineral and what your cattle have access to, loose
mineral mixes usually come in a 2:1 or 1:1 calcium:phosphorus
ratio. The first is for cattle with little access to feeds or
forage high in calcium, the former for those who have lots of
access to feeds high in calcium but little phosphorus. You will
need to check with your local feed supplier to see what mineral
supplement is right for you and your animals.