Have you ‘Herd’ of Cows?

 
Have you ‘Herd’ of Cows

Problem statement:

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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