Submitted to: Journal of Dairy Science
Publication Type: Abstract Only
Publication Acceptance Date: 3/21/2023
Publication Date: 6/25/2023
Citation: Miles, A.M., Van Raden, P.M., Hutchison, J.L., Fok, G.C., Schutz, M.M. 2023. Standardizing lactation yields from national data with age-parity-season-region corrections for fair comparisons across individual cows and environments. Journal of Dairy Science. 106(Suppl. 1):189-190(abstr. 2716).
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 have not been 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 animal model. The pedigree file included 91.3 million animals of all dairy breeds and crossbreds. Along with breeding values for those animals, the 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 period-region combination. The final adjustment factor then multiplies the two new age-parity and season-region factors with the original previous days open and milking frequency factors to produce a single multiplier. We observed that age-parity factors are reduced in recent decades, indicating faster maturity rates. 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 bring averages of standardized records much closer to actual herd averages. Seasonal effects are now estimated within five regions defined by each state’s average climate zone scores. Within each region the seasonal differences are smaller in recent decades, suggesting that improved heat abatement and management is decreasing the effect of the environment on lactation yields. These new factors were designed for application to lactation records in the national database and will be distributed to cooperators who also use standardized records to encourage the widespread adoption of a uniform approach to fair comparisons of lactation yields.