Extension Factors for Trimester Yields of Milk and Fat

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Abstract
Evidence or problems with sire proofs of extended incomplete records suggests the desirability of another method of evaluating dairy bulls for milk that minimizes the need for extending records by increased considering yields of 3 pairts of a lactation (days 1 and 90, 91-180 and 181-270) as distinct and separate traits. Records of < 90 days (or 180 or 270 days) require extension to 90 day (or 180 or 270 day) equivalents. Last sample dry production of 17,826, 15,282 and 12,115 1st lactation records of Holstein cows was used to calculate extension factors to predict remaining yields to days 90, 180 and 270 for mo., of freshing and days in milk. Cumulative remaining yield was computed as the product of days remaining to day 90, 10 or 270, yield on last sample day and the appropriate extension fctor. There were no differences in factors due to age, but factors were different for mo. of freshing and number of days in milk.