Estimating daily yields of cows milked three times a day

Factors to estimate daily yield from one or two sampled milkings of cows milked three times a day were derived with data for 21 mo from seven Pennsylvania herds and data for 1 yr from five Utah herds. Accuracy of estimation increased with number of milkings weighed; standard deviation of error was nearly halved when information was included from two milkings instead of one. Fat yield did not increase as much as milk yield with increased time between milkings (interval); therefore, fat percentage factors increased with interval. If fewer milkings were sampled than weighed, fat yield was estimated by adjusting sample-day fat percentage. Effect of interval on protein yield was nearly the same as on milk yield. Therefore, milk factors are recommended for protein, and no adjustment to protein percentage is necessary if fewer milkings are sampled than weighed. Factors derived for milk were tested on records from 53 California and Oregon herds. Standard deviations of errors were similar to those from Utah and Pennsylvania data.