In the coming months, 305-ME (Mature Equivalent) – the standardized production estimate last adjusted in 1994 – will be discontinued and replaced by 305-AA (Average Age). This change will incorporate current knowledge about the key variables that impact milk yield, improving the accuracy of the measure.
The new 305-AA yield estimates will appear in CDCB’s WebConnect data queries and be implemented in the calculation of CDCB genetic evaluations, expected in August 2024. Watch for more details about the coming implementation of the new 305-AA and the anticipated impacts on animal records and evaluations.
Dairy producers rely on a variety of measurements to compare animals of different ages, geographical locations and breeds. Whether using Net Merit $ to measure an animal’s genetic merit, Breed Age Average to compare type conformation, or the new 305-AA for milk yield, each tool is designed to help producers make informed decisions. As dairy herds evolve and as we learn more about cow performance, it is important we update these tools to remain relevant and accurate.
What’s the backstory?
Since 1994, the U.S. dairy industry has compared cows in different lactations, geographical regions and breeds using 305-ME (Mature Equivalent) adjustments. This production estimation standardizes milk, fat and protein yields to a 305-day lactation at a mature equivalent status regardless of a cow’s current age.
In 1995, a Journal of Dairy Science® paper authored by Norman et al outlined how genetic selection changes maturity patterns. Thirty years later, in 2023, the variables impacting the equation in the 305-ME estimations were reevaluated by USDA’s Animal Genomics and Improvement Laboratory (AGIL) and the Council on Dairy Cattle Breeding (CDCB). With CDCB’s stewardship of the National Cooperator Database, the dataset utilized in this review included 101.5 million milk records, 100.5 million fat records, and 81.2 million protein records!
The result of the 2023 AGIL-CDCB study is the introduction of 305-AA – an age-adjusted yield estimation standardized to a 305-day lactation record at 36 months of age – and the discontinuation of 305-ME.
How will the 305-AA differ from the 305-ME?
Before diving into the changes, let’s note the two variables that remain unchanged.
- The new 305-AA still standardizes lactations to a 2x milking frequency.
- The methodology for accounting for previous days open is unchanged.
Here are the primary changes:
- Age: Average Age adjustments standardize to 36 months. Mature Equivalent standardized to a range of 61-86 months depending on the breed.
- Climate: 305-AA includes five climate region adjustments accounting for cows residing in the hottest to coldest part of the U.S. The previous 305-ME region adjustments incorporated three geographical regions moving east to west across the U.S.
- Breed adjustments: Previously, breed adjustments were calculated along with the season-region adjustments but are now estimated along with the age-parity adjustments. Because of the increase in data over the past 30 years, smaller breeds are now more represented in age-parity adjustments where the prior 305-ME adjustments were heavily influenced by Holstein.
Source: CDCB