Economic Consequences of Replacing Cows with Genetically Improved Heifers

Abstract

A deterministic model of the dairy herd was used to investigate optimal cow replacement rates when genetic trends in milk ranged .0% to 1.0% per year. Optimal cow replacement rates maximizing net present value for the herd or maximizing milk sold per cow were insensitive to the extremes in genetic trends. Optimal replacement rates above a 20% involuntary removal rate indicated 0 to 3 cows among 100 should be culled on low yield for maximum net present value of herd females. Voluntary culling of 10 to 15 cows per 100 maximized milk sold per cow per year. At most an .04% increase in genetic gain per year occurred in intermediate cow replacement rates (range 28% to 32%) relative to the extremes (20% or 39%) when the best females were selected. These intermediate rates indicated a balance between opposing effects of a declining generation interval and a decreasing selection intensity among dams as replacement rate increased.Cow replacement rates which maximize net present value of all females in the herd, including reared replacements, are lower than rates which maximize the net present value of the cow herd only.