This decrease was the steepest September drop since the 8.4 percent year-over-year decline registered for September 1, 1999. Producers at that time were responding to negative returns that began in late 1997. The current lower breeding inventories are likely producers’ response to persistently negative returns that began late in 2007.
http://www.ers.usda.gov/Publications/LDP/2009/10Oct/ldpm184.pdf