Official Holsteincow performance data in Brazil, based on monthly milk weights, is calculatedusing the correction factors proposed by Everett & Carter (1968) to estimatethe partial production from calving to the first daily control in a given lactation.The adequacy of these factors was evaluated using 262 lactations from two herdswith daily control of milk production per cow. Data were divided into classesbased on age at calving (CIP): CIP 1 (up to 3 years), CIP 2 (3.1 to 4 years),CIP 3 (4.1 to 5 years), CIP 4 (5.1 to 6 years) and CIP 5 (above 6.1 years) whichincluded 104, 56, 44, 18 and 40 lactations, respectively. Milk yield from calvingto a set day of lactation was estimated with the official factors and assumingthat the first control of production of that given lactation occurred on days6th, 20th, 34th, 48th, 62ndor 75th. Estimated data was compared with real data calculated fromdaily milk weights. For all CIPs, official factors overestimated the productionfrom calving to first control and the relative overestimation error decreasedwith advance in the first control day. The overestimated amount of milk in thatperiod increased with advance in the first control day and was 13.9 and 87.1kg in CIP 1 and 20.6 and 196.3 kg in CIP 2 for days 6th and 75th,respectively. CIPs 3, 4, and 5 had intermediate values. New factors for firstcontrol days ranging from 6 to 75 and in all 5 CIPs were generated using thesame methodology described by Everett & Carter (1968). The generated factorswere smaller than the ones imported and routinely used to calculate officiallactation records in Brazil.
