Introducing 305-AA: the new national standardized yield measurement enabling fair comparisons across individual cows and environments

Authors: Miles, Asha; Van Raden, Paul; Hutchison, Jana; Fok, Gary; SCHUTZ, MICHAEL - University Of Minnesota

Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/5/2025
Publication Date: 11/1/2025
Citation: Miles, A.M., Van Raden, P.M., Hutchison, J.L., Fok, G.C., Schutz, M.M. 2025. Introducing 305-AA: The new national standardized yield measurement enabling fair comparisons across individual cows and environments. Journal of Dairy Science. 108(11):12463-12470. https://doi.org/10.3168/jds.2025-26275.
DOI: https://doi.org/10.3168/jds.2025-26275

Interpretive Summary: Multiplicative adjustment factors to standardize milk, fat, and protein lactation yields for age, parity, season of calving, geographical region, milking frequency, and previous days open were last updated in 1994. After 30 years of selection in concert with evolving management, the cows themselves have changed along with the environment in which they perform. The purpose of this research is to develop new methods for standardizing yields to allow fair comparisons across individual cows and environments, critical for value assessment, management decisions, and genetic evaluation. New factors were developed that account for breed-specific interactions with cow age as well as how climate region in combination with season of calving affects yields. Compared to the 1994 factors, these new methods better reflect breed-specific maturity rates and the smaller seasonal adjustments suggest cow management has greatly improved in the last 30 years, mitigating the negative impacts of heat stress. These new factors have been in use by the industry since August of 2024 directly impacting management and breeding decisions on farm.

Technical Abstract: Multiplicative adjustment factors to standardize milk, fat, and protein lactation yields for age, parity, season of calving, geographical region, milking frequency, and previous days open were last updated in 1994. Since then, the national animal model has estimated new adjustments within each 5-year period but those were not publicized or summarized until now. New estimates were obtained using 101.5 million milk, 100.5 million fat, and 81.2 million protein lactation records from 1960-2022 in a multi-trait model. The pedigree file included 91.3 million animals of all dairy breeds and crossbreds. Along with breeding values for those, the animal model included 392 unknown parent groups, 39.9 million permanent environmental effects, 1.3 million herd by sire interactions, and regressions on pedigree inbreeding and heterosis. New age-parity factors were estimated within each period-breed combination and new season factors were estimated within each time period-climate region combination. The new factors standardize records to 36 months and second parity instead of mature equivalent, which was already the policy in genetic evaluations since 2005, to make averages of standardized records much closer to observed herd averages. Seasonal effects are newly estimated within 5 regions defined by the average climate zone scores for each state. Within each region the seasonal differences are smaller in recent decades, suggesting that improved housing and management is decreasing the effect of the environment on lactation yields. The final adjustment factor then multiplies the 2 new age-parity and season-region factors with the original previous days open and milking frequency factors to produce a single multiplier. These new factors were designed for application to lactation records in the national database and have been distributed to cooperators who also use standardized records to encourage widespread adoption of a uniform approach to fair comparisons of yields.