Summit milk is the average of the two highest numbers of the first three test days production and is directly related to lactation yield. Studies show that for each 1-pound increase in summit milk, a cow will produce 225 to 230 pounds more milk for the entire lactation. As a rule, cows should peak eight to ten weeks after the onset of lactation, and peak milk production of first-calf heifers should be within 25 percent of older cows. The percent of first lactation animals in a herd is usually equal to the current culling rate. Although culling rates do vary, if a herd is making genetic progress and maintaining cow numbers, the percent first lactation animals is usually 25 to 30 percent.
Reproduction plays a major role in a herd s milk production level.
A cow will not produce milk until she first reproduces. Likewise, a cow will not increase milk production until she reproduces again. Calving interval is very critical as it affects stage of lactation, percent days in milk, and dry days. Calving interval also has a significant effect on the number of replacement heifers available. These programs would also aid in the use of artificial insemination, which is often needed in the lower production groups.