Heifers entering the herd are capital investments. This means a cow is in the average herd for about 2.7 years. These 2.7 years, divided by the 1999 average Michigan DHIA calving interval of 14.6 months, indicates a cow goes through about 2.2 lactations and 3.2 calvings before leaving the herd. Another way to analyze replacement costs is to calculate the cost per cow or per cwt of milk produced using the previous values. Cows in their third, fourth or later lactations can contribute considerably more to net income because they don't have the burden of repaying replacement costs.
Older cows make money.
The above information indicates that the average Michigan cow calves 3.2 times, but not all those calves make it into the herd. Using the above assumptions, it takes 2.7 calvings for a cow to generate her replacement. In Michigan, the average cow calves 3.2 times. If she must calve 2.7 times to replace herself, this leaves about a half calving to spare. Doing this math indicates that each cow only generates an extra 0.19 heifer.