For the farmer who takes care to keep them cool, providing them with

For the farmer who takes care to keep them cool, providing them with high-energy feed, and milking them regularly, Holstein cows are producing an average of 2,275 gallons of milk each per year.

Basis first, as this is an extreme use of modifiers coupled with pronouns and, most importantly, the meaning. To refresh our memories. "Ed" verbals are noun modifiers, and as noun modifiers, we need to place them as close to the noun they are modifying as we can. The prepositional phrases can be adverbial or modify the noun. Critical features of adverbials - we can place them a little far away as well. You'll see the implantation here.
For the ING, there are two ways to look at this sentence -
Comma + ING - it acts as an adverbial. It needs to make sense with the subject and verb before it.
ING + Comma - It acts as a noun modifier, modifying the immediate noun or subject.

Option Elimination -

(A) providing them with high-energy feed, and milking them regularly, Holstein cows are producing - Comma + ING is adverbial. What does it modify? "Farmer takes care." Does it make sense to say farmers keep cows cool by providing them food and milking them regularly? No. Check ING + Comma. Does it make sense that "cows" provide food and milk themselves? No. And we are saying "milk each per year," using continuous is wrong. This is the worst of all options. Full of mess.

(B) providing them with high-energy feed, and milked regularly, the Holstein cow produces - same issues. While it's okay to use ed or ING verbals on either side of "and" but here doing so messes up the meaning. "them" is plural; we need "cows." As if we could deal with modifiers, we have pronouns to deal with as well.

(C) provided with high-energy feed, and milking them regularly, Holstein cows are producing - "milking" the same issue. "are producing" wrong.

(D) provided with high-energy feed, and milked regularly, the Holstein cow produces - We have good modifiers but then pronoun issues.

(E) provided with high-energy feed, and milked regularly, Holstein cows will produce - Finally. Let's see a structure here.
Prepositional phrase (adverbial), Ed verbal (modified noun), clause. Now, let's unpack it. The basic structure is -
For the farmer who takes care to keep them cool, Holstein cows will produce an average of 2,275 gallons of milk each per year.
Now, the ed modifier "provided with high-energy feed and milked regularly" can only modify one noun, that's "cows," as farmers are not provided with high-energy feed, and farmers are not milked.
So, if we clear up the mess, we have two modifiers for "cows," one adverbial and one noun modifier. The noun has to be placed as close as we can. So we could either place it after cows (but that'll make this problem less difficult, and GMAT will not like that ), so the GMAT placed it before "cows" and even placed a prepositional phrase in the beginning, which, by the way, could have been placed anywhere. So the simplified version, which will make it a 600-level problem, is
For the farmer who takes care to keep them cool, Holstein cows, provided with high-energy feed and milked regularly, will produce an average of 2,275 gallons of milk each per year.

Hi IanStewart,

From just grammar point of view, can the modifier 'providing and milking' refers to the subject, which comes after it? If not, is it because the mentioned modifier does not start the sentence? Thanks