Quantifying the essential aspects of the lactation curve in an efficient and consistent way enables use of statistical methods in the study of many interesting and economically important questions, and increases our power to to detect and analyze factors influencing dairy productivity. MilkBot® models milk production as an equation with four parameters, each with a distinct meaning. These parameter values encapsulate the unique shape of a lactation curve, so that by observing parameter values we can make inferences about health and productivity. Alternatively, MilkBot can calculate such traditional attributes as time and magnitude of peak production, persistence of production, and cumulative or projected production.
Each MilkBot® parameter describes an aspect of the shape of the lactation curve, and is independent of other parameter values. It is reasonable to hypothesize that particular environmental factors, or particular interventions, will have characteristic effects on parameter values. This remains to be proven, but it is important to understand the individual meanings of the four MilkBot®parameters.
"Milkbot.Scale" (or "Scale") calculates an abstract overall capacity to produce milk, and can be expressed in units like pounds, kilograms, or liters. It can be calculated at any point in the lactation, from one or more milkweights. It is a theoretical maximum that is never quite reached in normal conditions, somewhat higher than actual peak daily milk. If the Milkbot.Scale increases by 10%, then predicted production increases by 10% for each day of the lactation. Peak milk and cumulative milk yield are also influenced by the shape of the curve, which is controlled by the other three parameters .
Milkbot.Ramp" (or "Ramp") measures how steeply milk production rises after calving, and is expressed in "days". If a cow comes into milk slowly, she will have a high Ramp value. Ramp values are useful in exploring transition management.
Milkbot.Offset" (or "Offset") measures the time between the day of calving and the beginning of lactation in a physiological sense. Changes in offset shift the curve to the left or right, and are measured in days. Without daily milk weights or large data sets, it is difficult to differentiate between the effects of offset and ramp parameters. For this reason, we often prefer the reduced parameter, peak day, a statistic influenced by both ramp and offset values. Both Ramp and Offset have their largest influence in the pre-peak portion of the lactation curve.
Milkbot.Persistence" (or "persistence") is a measure of the natural decline in production, expressed as a half-life. If a cow had persistence of 300 days, then she would be expected to drop in milk by 50% every 300 days. Infinite persistence would mean no drop at all. The effect of Milkbot.persistence in early lactation is obscured by the larger effects of ramp and offset parameters, but it dominates in late lactation. It also has a small effect on the peak day statistic.
Actual milk production on a given day is predicted by these four parameter values. Because each parameter has a known effect on the shape of the curve, it is easy to understand what changes in parameter values mean in terms of their effect on milk production. It is also straightforward to hypothesize what effect a given intervention might have on individual parameter values.
In many circumstances, understanding of parameters can be simplified by use of "reduced parameters" such as "Day of Peak Milk", a calculated value mainly influenced by Ramp and Offset values, but also slightly influenced by Persistence. Since Day of Peak Milk is also directly observable, it is a more natural expression of lactation curve shape than the primary parameter values which underlie it, and sufficiently precise for most applications.