Tool Overview

Since the use of simple averages, such as an average heifer breeding weight or an average age at first calving as heifer management benchmarks have limitations, the Heifer Pregnancy Rate Tool was designed by University of Wisconsin-Extension dairy specialists to provide a simple tool to calculate the true heifer pregnancy rate of an individual dairy herd's replacement heifers. Calculated true heifer pregnancy rate is a retroactive calculation and is the sum effect of heat detection, conception rate and variances within the herd in meeting heifer breeding criteria goals. After calculation, the management consequences associated with variance in the dairy replacement heifer breeding program are then expanded. Variances associated with heifer breeding efficiency are expanded in to range and variances in, days on feed, age of first calving and projected body weight variances at calving. In addition, the effects of heifer breeding efficiency on herd rearing cost and contribution of heifers to whole farm nutrient management are explored.


  • Download data entry spreadsheet

  • Enter your herd data into the downloaded spreadsheet. You only need to enter an ID and the Age at First Calving (month) for every animal.

  • Upload the spreadsheet back into the tool to perform the analysis.

Note: The current results correspond to the analysis of sample data contained in the data entry spreadsheet.

Upload Spreadsheet

Number of Heifers (sample data): 85

Calving Age (Averages and Variance)

  Your Herd Goals

Statistics Summary

Average age @ first calving, mo 23.7 23-24 mo
Minimum calving age, mo 21.6 n/a
Maximum calving age, mo 27.1 n/a
Heifers calving/year, n 85.0 n/a
Calving age deviation, mo 1.1 <1.7 mo
Kurtosis 1.4 n/a
Skewness 1.1 > 1.5

Range and Variance

Youngest calving age (typical), mo 22.1 > 21 mo
Oldest calving age (typical), mo 26.4 < 28 mo
Calving age range (typical), mo 4.3 < 6.0
Days on feed variance, d 131 < 200
Calving body weight variance, lbs 0.0 < 325

Breeding Efficiency

True heifer pregnancy rate©, %/mo 49.8 > 42.5
Average pregnancy age, mo 14.7 14.0-14.5
First (start) breeding age, mo 12.8 12.5-13.0

    © Copyright: Patrick C. Hoffman 12/3/2012

Rearing Cost

Excess rearing days, days/heifer 0.0 0 days
Excess rearing cost, $/heifer 0.0 $0
Excess herd rearing days, days/herd 0.0 0 days
Excess rearing cost, $/herd 0.0 $0

Nutrient Management

Excess manure production, tons/year 0.0 0 tons
Excess P production, lbs/year 0.0 0 lbs