Posted November 24, 2025
By A.J. Knowles, RAAA Director of Breed Improvement
As part of RAAA’s ongoing commitment to objectively describe and record cattle for its members, the Board of Directors has initiated the transition of EPDs produced by Colorado State University on a quarterly basis to EPDs produced by International Genetic Solutions (IGS) produced on a weekly basis. The transition will include the replacement of Maintenance Energy (ME) with Mature Weight (MWT), and a new Heifer Pregnancy (HPG) evaluation by the same name. Not only will these evaluations be more frequent, they will also include genomic data and be included in a multi-trait model, both of which drastically increase EPD accuracy. While these changes may sound big, it is important to remember that the biology underneath and selection emphasis remains the same.
The link between ME and MWT
ME is estimated using metabolic body weight, or mature weight raised to the ¾ power. Because the metabolic body weight is a simple linear transformation of the mature weight phenotype, the traits are highly correlated, often relating to one another at 98% or higher when estimated using the same data. This indicates that they are very nearly identical, and selection using either trait will yield nearly equal results. Changes in percentile ranking during the transition can be credited to the addition of genomics and a larger, multi-breed dataset housed at IGS. These additions increase the amount of information used to create an estimate of an animal’s genetic merit, which can change the resulting estimate.
Why Switch?
While the traits themselves are highly correlated, increases in model accuracy, and practicality in selection drive the move to publish a MWT EPD. For producers, mature weight is intuitive and familiar, allowing greater ease in visualizing, measuring, and evaluating the impact of selection for larger or smaller mature animals in their operations. The inclusion of genomic data and the multi-breed database have also increased accuracy, with the average individual EPD accuracy increasing from under 12% in ME to over 29% in MWT.
What does this mean for your herd?
Trait names and percentile ranks may change, but from a selection standpoint, the fundamentals remain the same. Cattle that have greater maintenance energy requirements also tend to have larger mature weights. The switch simply provides a straightforward, easily interpretable measure of the size and maintenance level required by an animal. While some reranking will occur with this change, it is expected to be minimal and driven by the inclusion of genomic data, the multi-breed IGS population, and slight model adjustments.
The transition is expected to go live on Wednesday, December 17th , when the MWT EPD will premiere in place of the ME EPD. The transition to a new Heifer Pregnancy model will come in the summer, alongside updates to the economic indexes. For any questions or more information on the release of the MWT EPD, please contact A.J. by email at [email protected]
