That count is way off.

An average cow is 600kg, and yields 36-48% in pure meat, so around 250kg.

McDonald's standard patty is 45g, while larger patties - say, like, the Quarter Pounder - go up to 120g.

Presuming 2/3 of all burgers per cow are regular, and 1/3 are Quarter Pounder size, then we have a simple formula to solve:

2x*0.045kg + x*0.120kg = 250kg

That makes X approximately 1190, so the total number of burgers is ~3570, over double of your calculations.