PreFresh Pen Size Calculator

Now available on iTunes.

The prefresh or close-up pen is the only pen in a dairy herd where the cow decides when she leaves. She alone determines the time of calving. This creates a potential bottleneck on the farm and results in overstocking at this critical time unless we over-build the area to alleviate stocking pressure during a calving surge.

Prefresh Pen Size Calculator screen shot

The purpose of this calculator is to predict the required group size for the prefresh pen based on estimates of herd size, calving seasonality, age distribution and target duration of stay.

refresh Pen Size Calculator screen shot


Enter the milking herd size, percent of the herd that is in the first lactation, the number of days each lactation group is in the pre-fresh pen, and the number of weeks it takes to fill the pre-fresh pen. Calculations will be done automatically. When finished you will receive the number of required pre-fresh pens and the average number of cows in the pens. You may email the results as a pdf by touching the email button. You may clear all data to begin another calculation by touching the Clear button.

Explanation of terms and data fields.

Months calving: allows the user to adjust for seasonally calving herds. Default is 12 for all year round calving.

Milking herd size: enters the 12 month rolling average or future estimate of the total herd size, including lactating and dry cows.

Freshening rate: assumes that the herd calves more cows than the average herd size. Typically herds calve 4-5% more cows than the herd size. Enter as 1.04 or 1.05 etc.

Percent Lactation 1: adjusts for the proportion of the herd that is comprised of first lactation heifers and assumes that in the future an equal number of heifers will enter the herd to maintain this proportion. Enter as a % eg. 40%.

Daily average calving rate: based on herd size and a 365 day year, determines the average number of animals calving per day

Days in prefresh pen: allows for the entry of the target duration of stay in the prefresh pen and permits a different duration for heifers and cows

Capacity adjustment: multiples the average daily rate of calving by a factor to facilitate overbuilding to avoid overstocking issues during a calving surge. For prefresh pen stays of 30 days or less, we recommend using a factor of 1.4. For longer pen stays >30 days, we recommend a factor of 1.3.

Total estimated prefresh capacity: delivers the estimated number of cows in each parity group and for the herd as a whole. This should be used to provide sufficient stalls (one cow per stall) or bedded area (minimum 100 sq ft or 10 sq m per cow).

Weeks required to fill prefresh pens: allows for different frequencies of pen filling. Typically pens can be filled weekly. However, if fewer larger pens are desired, that may be filled over multiple weeks, use this field to change the number of weeks. One week to fill pen = 1, two weeks to fill pen = 2, etc.

Number of required pens: based on the expected capacity required for the prefresh group and the capacity adjustment used, modified by the dry off rate used and the pen fill frequency, the number of required pens are calculated.

Cows per pen: adjusts the total estimated prefresh cows by the number of pens used to house them.

Now available on iTunes.