If you want to use a milk-production parameter to help judge how your fresh cows are doing, don’t use peak milk, Walt Guterbock, manager of den Dulk Dairy in
Lag. It takes 50 to 90 days to measure peaks, which means you have missed the critical fresh-cow period.
Momentum. If you average old peaks with new peaks, you obscure recent performance.
Bias. It doesn’t account for the cows that are culled or die before they reach peak milk.
Variation. If only a few observations exist, individual cows can skew the group average.
That’s why Guterbock prefers to look at the first-, second- and third-test-day milk production on all fresh cows.