I went to an ag conference January /2013, and was lucky
enough to hear Fred Provenza speak. He studied range science, was a professor and researcher in Utah and Colorado. One of the amazing things he had researched, complete with what substitutes for "double blind" in animal feeding behavior research, and animal nutrition research-- was that in what an individual animal eats depends partly on what the mama animal ate when pregnant.
This makes all kinds of sense, and leads to some astonishing conclusions, suggests many courses of action. In the case of the PI eating goats, it is likely that if you breed the females you have, and those females eat some PI while pregnant, the new goats will eat the PI more willingly, and will make better use of what's available in it.
Fred was able to get
cattle to eat artemesia as a fall winter forage. The rancher saved thousands of dollars because he did not have to buy as much
feed. A couple of important considerations: while they were eating the artemesia, mineral supplements were available, because the artemesia is not a complete feed for them, and they put the cattle on the artemesai range when the artemesia has the lowest levels of the compounds that make cattle avoid it.
Fred also quoted research which substantiates the idea that animals are able to choose feed (if available) that addresses any deficiencies the individual animal may be experiencing.
Get a few generations of goats eating that PI, and you
should see a big difference in how much of it they eat. Keep the big goat caveat in mind: don't have the only feed available be toxic to them, because they will eat it in those conditions. Have diverse choices for them, so that they can get what they need.
I hope this is helpful. I certainly have found it so.
Thekla