If you remove the first modifier clause and read the rest of the sentence by itself the correct answer will become obvious.

Provided with high-energy feed, and milked regularly, Holstein cows will produce...

Ron once said that the test takes some level of pronoun ambiguity Here, I see that we are struggling to set a referrent for THEIR.. Can't their refer to MANUFACTURERS logically ??? Besdies, I very well know that the answer should NOT include THEIR>. But just a thought crossed, please explain...!...