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305-day mature equivalent (305ME)

Definition

Section titled “Definition”

305-day mature equivalent (305ME) is a cow’s lactation milk yield standardized two ways:

  1. To 305 days. Completed lactations are cut at 305 days. Lactations still in progress are projected to 305 days from the test-day records so far, using standard lactation-curve shapes.
  2. To mature age and a standard calving season. Yield is multiplied by age–season factors so that a first-calf heifer or a cow calving in summer is expressed as if she were a mature cow calving in a standard season. Factors are breed- and region-specific.

The result lets you compare a 2-year-old at 60 DIM with a 5-year-old at 250 DIM, and compare herds with different age structures. 305ME is also computed for fat and protein.

305ME is an estimate. Early in lactation it rests on one or two tests and the standard curve shape, so it can move a lot as more tests come in.

Formula

Section titled “Formula”

Conceptually:

305ME = projected (or actual) 305-day milk × age–season factor


projected 305-day milk = milk to date + expected milk from today to 305 DIM
                         (from standard curve shapes and the cow's tests)
\mathrm{305ME} = \hat{M}_{305} \times f(\text{breed},\ \text{age at calving},\ \text{calving month},\ \text{region})

The projection method and factor tables belong to each processing system (DHI processing centers, DC305). A crude proxy such as “total milk to date × a single factor” or “test-day milk × 305” is not a 305ME.

How to pull it in DC305

Section titled “How to pull it in DC305”

305ME is a standard DC305 item. It is calculated on the fly from test-day records and age at calving, not stored in the cow file, so it changes after each test and is not present as a stored value in raw backup files.

LIST ID LACT DIM 305ME FOR LACT>0
SUM 305ME BY LACT FOR LACT>0 DIM>60
SUM 305ME BY PEN FOR LACT>0 DIM>60

User-defined production items, and any herd-specific DIM cutoff, vary by herd; check the herd’s private dc305-vocab mapping. See DC305 item codes.

Typical range

Section titled “Typical range”

Herd context: US Holsteins, freestall or dry-lot, 3x milking, DHI-tested.

Herd level Average 305ME milk (lb)
Typical 25,000–29,000
Good 29,000–32,000
High > 32,000
  • By parity: because of the age adjustment, first-lactation and mature cows in a well-managed herd should have similar 305ME. First-lactation 305ME well below mature-cow 305ME points to heifer-raising or transition problems.
  • Stability: 305ME for cows under about 60 DIM is volatile; exclude them when ranking.

Common mistakes

Section titled “Common mistakes”
  • Treating 305ME as actual milk. It is a projection plus an adjustment. It is not what the cow shipped, and it doesn’t tie to the milk check.
  • Building a proxy and calling it 305ME. Total milk × a factor, or test-day milk × 305, ignores curve shape and age–season effects.
  • Ranking very fresh cows. One early test drives the whole projection.
  • Comparing 305ME across systems. DC305, DHI processing centers and other software use different factor tables and projection methods.
  • Reading 305ME from an old export. Because DC305 calculates it on the fly, an export reflects only the tests available on the day it was made.
  • Ignoring milking frequency. Comparing a 2x herd with a 3x herd without knowing how the factors treat frequency.
Section titled “Related”