Extending Partial Lactation Milk and Fat Records with a Function of Last-Sample Production

Abstract

Holstein production records (364,328) 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 + .**GRAPHIC**. production)] .cntdot. (305-n). The coefficients (b) were estimated within 3 stages (< 65, 65-245, > 245 days in milk), 4 age at freshening groups (< 34, 34-48, 49-60 and > 60 mo., 34-36 mo. cows were placed in the 1st group if freshening for the 1st time), 3 herd yields (< 5900, 5900-7000 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.