Have You Herd Of Cows Puzzle

The Puzzle:

Have You Herd Of Cows
Old Farmer Palmer has a herd of cows, but he always seems to forget how many animals there are. When he counts them he just makes sure he can see 6 cows from each window of his house:

One night, however, Russell the Rustler took away half of the herd. Farmer Palmer didn't notice for ages because the next morning he could still see 6 cows from each window. How was it done?

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