Four numbers describe where a cow sits in her year. They are easy to confuse and only one of them is really about money.
Days in milk is simply the number of days since a cow calved. It is the backbone of every production comparison, because a cow at 40 DIM and a cow at 280 DIM are not supposed to give the same amount of milk. A herd's average DIM also tells you the shape of the year ahead: a low average means most cows are early in lactation and the tank is about to be full, a high average means the opposite is coming.
The voluntary waiting period is how long you deliberately wait after calving before you breed a cow again, usually 50 to 60 days. It is voluntary because it is your choice, not the cow's biology: the uterus needs time to recover, and breeding too early gives poor conception. Setting it longer than about 70 days rarely pays unless you are managing a specific problem, because every day of waiting is an open day you chose.
Days open is the gap between calving and the service that actually got the cow pregnant. It is the number that costs money, because a cow that stays open keeps eating while her milk yield falls and her next lactation is pushed further away. Most herds aim for 100 to 130 days. Watch the distribution rather than the average: a handful of cows at 250 days open will drag a herd figure that otherwise looks healthy.
Calving interval is the time between one calving and the next, and it is really just days open plus gestation. Around 12.5 to 13 months is a common target. It is a lagging number — by the time it moves, the decisions that caused it are a year old — so use days open to steer and calving interval to check.
Not always. Very high-yielding cows can still be giving a lot of milk when a short interval would have them dried off, and pushing them to rebreed early can cost more than it earns. The useful question is not how short the interval is but whether each cow is open longer than she needs to be.
Most herds target 100 to 130 days, which pairs a 50 to 60 day waiting period with prompt heat detection and decent conception. Above about 150 days there is usually a specific cause to find — missed heats, poor conception, or a group of cows nobody has made a decision about.
Yield rises to a peak around 40 to 70 days in milk, then declines steadily. Comparing cows without adjusting for DIM makes early-lactation cows look like stars and late-lactation cows look like culls, which is how good cows get sold. Compare like with like, or use a measure that already accounts for stage of lactation.
DocDairy works these dates out for every cow the moment you record a service, and puts the ones due today on one printable list. Ten languages, offline in the barn.
Try the live demo See pricing