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Heifer survival to calving

Definition

Section titled “Definition”

Heifer survival to calving (also called heifer completion rate) is the share of heifer calves born into a herd, and kept as replacements, that reach first calving. It sums up every loss between birth and first freshening: calf deaths, post-weaning deaths, and heifers removed for poor growth, injury or failure to conceive.

The basis is heifer calves born alive, minus heifers sold. Heifers sold as calves (surplus heifers, beef-cross heifers sold young, heifers sold to another dairy) were never going to calve in the herd. Counting them as losses would make a herd that sells surplus heifers look like it has poor survival. Removing them from the denominator measures only the heifers the herd actually tried to raise.

The simplest version counts only deaths as losses: survival = (born − sold − died) ÷ (born − sold). A stricter version also counts heifers culled for failure (open, chronic pneumonia, poor doer) as losses, because they were raised but never calved. That needs a sale reason that separates a marketing sale from a failure cull. State which version is reported; if the data can’t separate the two, report the simple one and say so.

It is measured on a birth cohort: all heifer calves born in a period, followed until each has calved, died or left.

Formula

Section titled “Formula”

Plain text:

Survival to calving (%) = (born alive − sold − died) / (born alive − sold) × 100


Strict version:
Survival (%) = heifers from cohort that calved / (born alive − sold as surplus) × 100

LaTeX:

S = \frac{B_{\text{alive}} - N_{\text{sold}} - N_{\text{died}}}{B_{\text{alive}} - N_{\text{sold}}} \times 100
\qquad
S_{\text{strict}} = \frac{N_{\text{calved}}}{B_{\text{alive}} - N_{\text{sold, surplus}}} \times 100

A cohort is only final when every heifer in it has calved, died or left. For Holsteins that is roughly 26–30 months after the last birth in the cohort. Before then, report survival “to date” with the number of heifers still growing.

Survival by stage is often more useful than the single figure:

Survival = S(0–60 d) × S(61 d to breeding) × S(breeding to calving)
S = S_{0\text{–}60} \times S_{61\text{–breed}} \times S_{\text{breed–calve}}

How to pull it in DC305

Section titled “How to pull it in DC305”

Heifers are LACT=0 animals with a birth date (BDAT). Those that have calved have LACT≥1. Deaths and sales are herd-defined events with a date; DC305 keeps animals that left in the archive (dead/sold) file.

COUNT FOR BDAT>-1095 BDAT<-730                cohort still in the herd (live only)
COUNT\B FOR BDAT>-1095 BDAT<-730              whole cohort, live and left (sold or died)
COUNT\D FOR BDAT>-1095 BDAT<-730              of those, animals that have left
COUNT FOR BDAT>-1095 BDAT<-730 LACT>0         still in the herd and calved
EVENTS\D DIED ID BDAT FOR BDAT>-1095 BDAT<-730   deaths in the cohort, with remark
LIST\D ID BDAT SELDT DIEDT FOR BDAT>-1095 BDAT<-730   leavers in the cohort with sold (SELDT) and died (DIEDT) dates
EVENTS\D SOLD ID BDAT FOR BDAT>-1095 BDAT<-730   sales in the cohort, with remark

COUNT, LIST and EVENTS cover live animals only by default; \B adds animals that have left the herd (sold or died) and \D gives those alone. Animals moved to the archive file are read with \L on EVENTS. Count deaths and sales by removal event or code. RC 7 marks sold/died animals.

Sale reasons (“sold as surplus calf” vs “sold as poor doer”) are herd-defined. Check the herd’s private dc305-vocab mapping. Heifers raised off-site at a calf ranch or heifer grower may have deaths entered late or in bulk.

Typical range

Section titled “Typical range”

Herd context: US Holstein heifers, raised on the dairy or at a contract grower, freestall or dry-lot dairies.

Measure Typical Goal
Birth to first calving (sold excluded) 80–90% > 90%
Birth to weaning 92–95% > 95%
Weaning to first calving 90–95% > 95%

Common mistakes

Section titled “Common mistakes”
  • Counting heifers sold on purpose as losses, or leaving them in the denominator.
  • Recording failure culls as plain “sold”, which hides real losses under the strict version. Record a sale reason.
  • Including stillbirths in “born”. Use heifers born alive; see stillbirth rate.
  • Reporting open cohorts as final. Heifers still growing are neither survivors nor losses yet.
  • Missing early calf deaths that never got an ID.
  • Mixing beef-cross and dairy heifers when beef-cross heifers are never meant to calve in the herd.
  • Including purchased heifers. Survival describes heifers born in the herd; animals bought in belong in a separate count.
Section titled “Related”