EXTENDING PARTIAL LACTATION MILK AND FAT RECORDS WITH A FUNCTION OF LAST-SAMPLE PRODUCTION

Holstein production records (364,328) from the Northeast were used to develop a procedure to extend in-progress and terminated records. A function was developed involving last-sample production which accounts for systematic influences in estimating remaining yield, which is yield from day of last sample to day 305. Last-sample production was used because remaining yield is estimated more accurately from last-sample production than from cumulative yield. The function is: estimated 305-day yield = yield in first n days + [(b1 + b2n) last production + (b3+b4n)/last production)]· (305-n). The coefficients (b's) were estimated within three stages (<65, 65 to 245, >245 days in milk), four age at freshening groups (<34, 34 to 48, 49 to 60, and >60 mo, 34 to 36 mo cows were placed in the first group if freshening for the first time), three herd yields (<5900, 5900 to 7000, and >7000 kg), and six 2-mo season-of-freshening groups by least squares for milk and fat yield. Cumulative yield factors were developed from the same data and compared with this function. The last-sample function had smaller error variance. © 1979, American Dairy Science Association. All rights reserved.