Flexible testing and use of milk-only records
P.M. VanRaden, G.C. Fok, L.R. Bacheller, G.B. Jansen, E.L. Nicolazzi, and J.A. Carrillo
Effective with the April 5, 2022 evaluations, edit programs were revised to begin using milk-only records in the multi-trait evaluation of yield traits. Other trait groups such as cow fertility and health also will have a greater number of usable records, because edits for those traits require usable milk yield records. Previously, national genetic evaluation software required that fat yield was recorded, and milk-only records were excluded. We estimate that this edit adds nearly 900,000 milk-only records for the relevant traits.
Cows with milk-only records will have evaluation code set to 5 in byte 110 of format 105.
Milking systems often can accurately measure and record milk volume, but inline estimation of milk components is more difficult. Since 1998 when data collection ratings (DCR) were introduced, milk and fat received the same weight calculated as an average of the DCR values for milk and components, instead of separate weights, because of software limitations. Most milk-only records are unsupervised and therefore get the same reduced weights and extra edits for percent milk shipped and percentage of valid sire ID as other owner-sampler herds.
Lactation weights for milk, fat, and protein now use three separate DCR based on the testing patterns and correlations among test days within lactations. Herd variance ratios had been estimated from one trait (milk yield since 1992 and then fat yield since 2007) and applied to adjust all three traits (milk, fat, and protein). To include milk-only records, separate trait-specific variance adjustments and weights were developed and applied to each trait. New and official genetic evaluations were compared from December 2020 data. Numbers of usable lactation records were 98,269,605 for milk, 97,393,419 for fat, and 78,044,073 for protein, indicating that 876,186 milk-only records were added. Correlations of new with previous Predicted Transmitting Abilities (PTAs) were > 0.9995 across all bulls for all three traits and were > 0.997 for bulls born since 2007 with > 50% reliability. The standard deviation (SD) of PTA increased slightly by 2.4% for milk, 0.1% for fat, and 0.4% for protein but reliability also increased slightly from the extra records.
Further research could help adapt to more flexible testing options and automated data collection that continue to increase in popularity.