The overall objective is to test the new strategy, a 18 months calving interval against a traditional
12 months calving interval, on four commercial farms with an average of 150 cows and investigate
effects on production, as well as the necessary management adjustment. Cows are blocked and allocated randomly at the 2 treatments, which only differ in time for first insemination. The specific objectives are to quantify the effects of an extended calving interval on milk production, persistency and milk quality, body condition in late lactation, reproduction and transition cow problems of the individual cow based on comparative studies within four herds. Effect of feeding method and milking frequency will be evaluated between herds.

Expected outcome:
1) At least the same milk production (kg ECM/cow/year) from cows on a strategy with an 18
months calving interval compared with 12 months, 2) improved results from reproduction measured
as inseminations per pregnancy from cows on a strategy with a 18 months calving interval.
Some cows are expected to be more suitable for extended lactation, and we 3) expect to identify specific characteristics of these cows to support a future reproduction strategy based on an optimum
calving interval of the individual cow within the herd.