A review of once-a-day milking in dairy cow grazing systemsPresented as part of the Joint ADSA Midwest Branch/Forages and Pastures Symposium: Grazing to Improve Profitability of Midwest Dairy Farms held at the ADSA Annual Meeting, June 2022

[Display omitted] •Milking OAD during the whole lactation is practiced in about 10% of New Zealand herds.•An OAD milking production system reduces milk production per cow, but improves cow fertility and quality of life for the farmer and farm staff.•Cows suitable for OAD can be produced by sires selected on an OAD-selection index. Twice-a-day (TAD) milking during the whole lactation is practiced in about 55% of New Zealand herds and once-a-day (OAD) milking during the whole lactation in about 10% of herds. The remainder of farmers use a mixture of TAD and OAD. Results from long-term comparisons show that over a full-lactation cows milked OAD, on average, had lower yields of milk (27%), fat (23%), and protein (24%) and higher percentages of fat and protein than cows milked TAD, but cows milked OAD for the entire lactation had better reproductive performance. Herds of cows milked OAD have higher mean 3-wk submission rate, 6-wk in-calf rate, and conception to the first service, and lower not-in-calf rate than the herds of cows milked TAD for the entire lactation. Farmers that have adopted OAD milking have culled cows that are unsuitable for OAD, and used sires selected on a OAD selection index to produce cow replacements that are more suitable for OAD milking. This OAD index includes the same traits that are included in the New Zealand national selection index with different relative economic weights on these traits plus including udder support, front teat placement, milking speed, and body capacity. A pasture-based milk production system based on OAD can be an alternative for many dairy farmers to maintain or increase farm profitability, with the additional benefits of better cow fertility and flexibility of using labor.