I found this on alt.callahans as posted by Randy Martens.

Randy, smiling mischeiviously, sits down by the fire and begins to spin a tale:

You see, the place where I grew up in Central New York State was serious farming country — apple, dairy, and other fruits such as berries were the biggest items.

Well, there was one farmer, name of Mayne, who consistently won the state prizes for the best milk and milk products. He was quite sucessful financially, and his farm was large enough that he needed a small helicopter to get around it.

One day, some officials from the State Dairy Borad droppped in to talk to him. The Chairman, his Assistant, and Mr. Mayne all got in the helicopter and took a flying tour of the pastures.

As they were flying by, the Chairman noted that despite the huge acreage, many of the cows were congregated in one pasture, whose ground cover was much darker green than the rest. The Chairman asked about this, and Mr. Mayne replied “Oh, yes. That’s part of my secret, you see. Some years ago I bought out part of the land belonging to one of my neighbors, who was a fruit farmer. Anyway, he’d planted strawberries, and I just let the cows eat them, intending to replant later. Well, the cows that had been pastured out there produced much more milk, and of higher quality, that I planted more berries for them to eat, and you have seen the results.”

The Chairman nodded, and said “I should have realized that — it makes sense: strawberry fields for heifer.”