BoviSync has items for weeks in milk that go from Week 2 Milk to Week 36 Milk. These items are influenced by both parlor weights and DHI test day data. Weeks in milk that are greater than a cow's days in milk are extrapolated values and are used to help predict the trend of a cow's lactation curve. We can project weights into the future because of how these items are extrapolated. To understand more of what extrapolation means, here is a definition.
Extrapolation is an act or instance of inferring an unknown from something that is known. In mathematical statistics, it's the act or process of estimating the value of a variable or function outside the tabulated or observed range. It is an estimation of a value based on extending a known sequence of values or facts beyond the area that is certainly known. In a general sense, to extrapolate is to infer something that is not explicitly stated from existing information.
As a cow gets more parlor weights or test day data, the earlier numbers aren't extrapolated but become the actual values. "Week in Milk" is an accurate measurement of current and past data equivalent to the stage of lactation (or DIM) the cow is in. The values that are beyond the current stage are an extrapolation of the cow's past performance. If she is increasing with milk test and parlor weights, those extrapolated values will be increasing on a trajectory equivalent to the past increase. If she is decreasing, the trajectory will be a decrease. The rise or fall of the "Week in Milk" in the future will tell you if she is continuing to increase or decrease. Also, If a cow happens to have a health issue and falls off in milk, or is tested during this drop-off, the extrapolated weeks will reflect that. If her health issue was so drastic that her milk plummeted, her future weeks in milk will show that same sharp drop but BoviSync will not show a negative value. Likewise, if her parlor milk is interrupted even though she is fine and healthy, and her average drops, her future weeks in milk will reflect that too.
In BoviSync, the week in milk is extrapolated for four weeks into the future from the current stage of lactation (or DIM). So, if a cow is 28 DIM or in her fourth week, her "Week in Milk" will be extrapolated out to Week 8 Milk. As stated at the beginning of the article, the greatest week in milk goes to week 36 or about 250 DIM.