My father's goats love pine, not just the needles but the young and flexible twigs too.
So much so that most of the pinetrees in the feeding area lost the branches under 1,5 meters or so.
They never had a miscarriage, but had a lot of false pregnancies.
I do not know if those have anything to do with pine.
sustainability.stackexchange.com/users/894/András
I have been told that pine is a natural de-wormer for goats.
I always give mine a few descent size branches when they show signs of worms.
They usually will try their hardest to get to the branches even when they have plenty to forage on.
Never had any issues and the worm problem is usually eliminated.
sustainability.stackexchange.com/users/5762/Joe Ramunni
There is quite a lot of info on the web in general, from this big list of poisonous and ok plants (repeated in various places with no source or attribution - pine is on the ok side).
A more definitive answer comes from this summary of two research papers containing this excerpt: No abortions occurred, however, toxicity was observed in the 3 treated groups.
The pine tips were most toxic, the bark less toxic and the needles least toxic.
Clinical signs of toxicity included muscular weakness, trembling, unusual stance, rumen stasis, bloating, opisthotunus, depression, loss of appetite, and death.
Necropsy revealed no significant gross lesions.
Pine needles, tips, or bark do not cause abortions in goats but are potentially toxic…"
My experience is that goats will eat pine trees if given the opportunity, so it's probably wise to keep pregnant ones away from the trees.
But they do generally seem to prefer grass and trees with bigger leaves.
My experience of goats eating young trees (including pines) suggests that that should apply to any tree you don't want the goats to eat.
Note that goats are climbers, and will eat much more of the tree than you would expect, if they can get access.
sustainability.stackexchange.com/users/659/Móż
Some pines can act as abortifacients and possibly cause renal damage because they contain isocupressic acid.
Ponderosa pine is the one I know of, because we have some near our goat pasture and have to keep them fenced out of it.
I have heard that juniper and a few other conifers might have this problem too.
On the other hand, our goats love douglas fir needles and young bark, and have eaten it regularly for 9 years with no miscarriages.
sustainability.stackexchange.com/users/5274/Peter Bergin
Well, it seems a little is ok.
I think we have over done it with out goats, given them too much too quickly.
Seems to be a problem with gut bacteria and not having time to adjust to the new feed.
We had 2 huge pines cut down in the yard and have been chucking branches into the goat pen all week, so they don't have much choice.
Bad move -
our one doe couldn't get up last night and is very week and bloated, all the others look ok, but seem like they have slight signs of bloat and weekness.
There was a study that someone referred to in a post about this very issue, it suggested that the tips are the more toxic part, and if they have too much
it's a problem.
Bottom line: I think if you have decent pasture they will eat a bit of everything.
Don't feed them pine exclusively.
sustainability.stackexchange.com/users/3619/Ruth Coates
I have a goat that's been sick for years and
the pasture she's in is in the middle of a pine forest (bull pine to be exact).
Whenever she's out and about she always takes a nibble on some pine trees and it's impossible to get her away until she is satisfied.
I found a way to use this to my advantage and even out the harmful with the helpful.
I take molasses and glaze some over the pine trees, to single out the trees they like, and then I put about half a cup of loose minerals over it.
It encourages them to eat their minerals and to lessen the amount of pine they eat.
sustainability.stackexchange.com/users/5401/cliff
I'm finding seemingly contradictory information with a normal search (forums).  Many sources say that their own goats love pine needles and there's nothing wrong with letting them eat them.  Occasionally somebody jumps in to say that pine needles can cause a miscarriage in bred does.  I suppose both can be true.  Any reliable source of info out there?
Are pine needles poisonous to goats?
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sustainability.stackexchange.com/questions/1241
sustainability.stackexchange.com/users/392/Tim Lehner
Some say that pine is a natural de-wormer for goats and pine is generally considered to be not particularly poisonous to goats. However, some pines can act as abortifacients and possibly cause renal damage because they contain isocupressic acid.    Pine can be a natural de-wormer and is generally OK for goats, though some are abortifacients and may cause renal damage.
Pine appears to be OK for goats and is a natural de-wormer. Some pines are abortifacients and can cause renal damage.