The traditional approach to sizing close up and fresh pens is to calculate the average number of calvings per week by dividing the total number of calvings in the past year by 52 weeks per year. Then the average number of calvings/week is multiplied by the target number of weeks in the pen. For example, if a dairy has an average of 20 calvings per week and the planned duration of stay in the close up pen is 3 weeks, most planning manuals suggest that the close up pen should be designed to house 60 cows. By definition, pens designed in this manner are overstocked half of the time.
We prefer to build special needs pens to accommodate the surges in numbers of special needs cows. Based upon a review of a number of Midwestern herd records, we have recommended sizing close-up and fresh pens for 140 percent of the average number of calvings. In the example from the paragraph above, we would recommend provision of not 60, but 84 stalls in the pre-fresh pen with an available bunk that is 73 meters (240 feet) in length. Sizing these pens on this basis will mean that these pens are overstocked less than 10 percent of the time. There are also times when pens sized on this basis appear to be substantially under-stocked, or as some would say, “grossly overbuilt.” Our estimations of the impact of this practice suggest that this makes economic sense. Each stall and headlock in a pre-fresh pen has a multiplier effect in that it impacts the start of 10 to 15 lactations each year.