The number one reason is that flies take away from cattle weight gain which in turn results in money out of your pocket. Secondly, feed conversion is lowered by an abundance of flies. Finally, cattle with flies are not as healthy and cow milk production may be lowered resulting in lower milk availability for calves.

NOTE: Only 200 flies per head can make an economic impact in your herd; i.e. profit. (Progressive Farmer: May-June 2002; pg. MS-16)